The Use of Fog Generators in Integrated Vector

Transcription

The Use of Fog Generators
in Integrated Vector Control*
*
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Thermal Fog & Cold Fog (ULV) Generators
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Prepared by LUCIEN SWILLEN
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TABLE OF CONTENTS
ChapterPage.Page
1Introduction
2
What is space spraying?
3Equipment
4
5
6
7
8
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1
....................................................................................................................................................................................
2
........................................................................................................................................................................................................................................
4
Air-shear droplet generators........................................................................................................................................................................................................... 4
Rotary droplet generators.................................................................................................................................................................................................................. 4
Thermal foggers........................................................................................................................................................................................................................................... 5
Thermal foggers v’s Cold foggers ............................................................................................................................................ 6
Droplet life span.................................................................................................................................................................................................................... 8
Details on thermal foggers with regard to the operating temperature........ 11
Procedure, Timing and Frequency ULV Space Spray Operations................. 13
Vehicle-Mounted Fog Application with Thermal Fog Generators
or ULV Space Spray Applicators................................................................................................................................................. 15
Fogging Techniques.............................................................................................................................................................................................................................. 15
Calculations................................................................................................................................................................................................................................................... 16
9
Portable Thermal Fogging ..................................................................................................................................................................... 19
10
Motorised Back-Pack Fogging (with or without ULV attachments)............. 27
11
Fogging with Hand Held Equipment................................................................................................................................ 31
Calculations................................................................................................................................................................................................................................................... 26
Calculations................................................................................................................................................................................................................................................... 30
12Annexes:
............................................................................................................................................................................................................................................
32
1 Preparation of Spray Solution to kill adult mosquitoes during DHF outbreaks........................................................... 32
2 Safety Precautions and Other additional safety instructions and accident prevention....................................... 33
3 Directions for determining the droplet size of Malathion/Maldison non thermal aerosols........................... 35
13 Selected References
14 Abbreviation References
15Acknowledgements
Cover photo acknowledgement: Swingtec
..............................................................................................................................................................................................
41
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42
.................................................................................................................................................................................................
43
1 INTRODUCTION
In this manual, the writer will explain about thermal foggers, cold
foggers, and mist blowers, as well as application techniques, space
spraying, fogging aerosol spraying.
The writer will also explain the clear distinction between the different
applicators, and application techniques to avoid confusion.
Fogging or space spraying is only possible with:
• thermal fogging machines (either mobile mounted or hand carried)
• truck mounted Ultra Low Volume (ULV)u space spray applicators.
• special hand carried ULV machines and
• special ULV backpack space spray machines
The standard backpack mist blowers produce a droplet spectrum
which is much larger than the ULV applicators. Droplets stay
airborne only for a very short time while the reach of the spray
cloud is rather limited. Also the droplet spectrum and the reach of
mist blowers which are equipped with so-called ULV attachments
cannot be compared with the droplet spectrum and reach of real
ULV space spray applicators and thermal fogging machines that
produce appropriate particle sizes.
It is only with either thermal fogging machines, truck mountable
or special ULV space spray applicators, that real fog or space
spraying applications are possible. Fog or space spray application
require a droplet spectrum with a Volume Median Diameter
(VMDv) of less than 30 µm, and an application rate in the range
of 0.5 to 6 Litres per hectare. According to the latest scientific data,
droplets between 10 - 15 µm (µm = micronw) are estimated as
ideal for adult mosquito control, while mosquito larvae stages
require droplet size >50 µm. These types of droplets stay airborne
for a long time and dependent on wind conditions, target
distances of 50 to 100 meters, can be achieved. This result is not
possible with mist blowers with or without ULV attachment.
Footnote:
uULV: Ultra Low Volume is generally defined as using very low volumes of spray per unit area compared to conventional spraying with hydraulic
nozzles (generally less than 5.0 L per hectare).
vVMD: Volume Median Diameter, expressed in µm. 50% of the droplets are smaller than the VMD and the rest are in larger droplet sizes. A few large
droplets can significantly change the VMD. The value of the VMD does not indicate the range of droplet sizes. Sometimes referred to as MMD (Mass
Medium Diameter).
wµm: Micron where a µm = 1/1,000 mm.
1 | The Use of Fog Generators in Integrated Vector Control: Thermal Fog & Cold Fog (ULV) Generators
2 WHAT IS SPACE SPRAYING?
A space spray, technically an aerosol, is a liquid insecticide
launched into the air in the form of hundreds of millions of
tiny droplets, ranging from 1-30 µm VMD. Modern Ultra Low
Volume applicators are designed to deliver optimum droplet
size of 8-20 µm VMD. This may be generated by either Thermal
Fogging (where a thick fog is produced) or by Ultra Low Volume
(ULV) generator where the droplets are produced by an aerosol
generating machine (no fog cloud).
To avoid developing resistance to the insecticide during the space
spraying, it is desirable to discourage long term treatment of
dengue fever and malaria. It is important to understand that adult
control of both vectors is difficult due to daytime activity cycle for
dengue vector and resting area for malaria vector.
Treatment at an interval of 1-2 weeks with vehicle-mounted
applicators, (which are used for huge open space areas) and
portable fogging applicators, (for areas where the vehicle
mounted units access is impractical), could give some valuable
results. Space spraying with insecticides should be considered
an epidemic contingency measure. Total coverage should be
focused to treating houses and in places where high vector
densities have been recorded.
Space spraying should be implemented in a compact
community and should be within a radius of 400-500 meters of
the affected houses.
EFFECTIVE SPACE SPRAYING IS DEPENDENT UPON
THE FOLLOWING SPECIFIC PRINCIPLES:
Target insects are usually flying through the spray cloud (or
are less often impacted whilst resting on exposed surfaces).
The efficiency of contact between the spray droplets and target
mosquitoes is therefore crucial. This is achieved by ensuring that
spray droplets remain airborne for the optimum period of time
and that every fog droplet should contain the lethal dose and the
correct size for a mosquito adult.
These two issues are largely addressed through optimizing the
droplet size.
• If droplets are too large they fall on the ground too quickly
and don’t penetrate vegetation or other obstacles encountered
during application (limiting the effective area of application).
If one of those large droplets impacts an individual insect
then it is also ‘overkill’ since a high dose will be delivered
per individual mosquito, wasting insecticide. Of course this
does not refer to thermal fogging machines and genuine ULV
space spray applicators. These machines do not produce large
droplets if correctly adjusted.
• If droplets are too small they may not hit a target mosquito
(no impaction) due to aerodynamics or they can be carried
upwards into the atmosphere by convection currents or wind.
OBJECTIVE:
ADULT STAGE AND ITS CONTROL:
The objective of space sprays (thermal fogging and ultra-low
volume aerosol sprays) in vector control is to achieve a rapid
knockdown and mortality of the adult Aedes or Anopheles vectors
especially under epidemic conditions. They should be employed
in situations of emergency for Aedes or Anopheles control to
suppress and interrupt an on-going dengue or malaria epidemic
or to prevent an expected dengue or malaria outbreak from
occurring. Adult Aedes or Anopheles vector densities, especially
the older and potentially infected populations, should be reduced
to sufficiently low levels to prevent or interrupt transmission.
Some mosquito species prefer an indoor habitat where they
rest during the day and attack at night. Other mosquitoes
remain outdoors.
Desirable spray characteristics include:
• a sufficient period of suspension in the air
• suitable drifts characteristics and,
• penetration into target areas with the ultimate aim of impacting
on adult mosquitoes.
WHY USE SPACE SPRAYING?
Only the female adult mosquito can transmit vector born diseases.
Space spraying is recommended in situations where habitat source
reduction has failed to limit the production of mosquitoes and the
risk of disease transmission is high. The objective is to reduce the
adult female population as quickly as possible.
The resting areas of the dengue vector (i.e. Aedes aegypti) are a
bit different from the ma;aria vector. The dengue vector will rest in
any shaded place and under any surface to give them protection
from desiccation and predators as well as from physical harm.
Normally and contradictory to the malaria mosquito, the dengue
vector rests up to a certain height. Once this height is known it’s
unnecessary to spray above this border line. However the eaves,
which are sometimes situated above the mentioned border line,
but which are perfect resting places for mosquitoes, should be
also treated. Correct space spraying techniques must able to get to
some of those protected spaces.
• INDOOR ADULT MOSQUITOES:
Indoor resting mosquitoes are easily controlled using a volatile
fogging insecticide formulation combined with the small fog
generator, equipped with a nozzle system providing extremely
small droplet sizes. Droplets < 10 µm have the advantage
remaining airborne for longer periods and can penetrates in
protected locations like corners and cracks where mosquitoes
rest. Such fogging applications does not result in wet or humid
surfaces. For example: writing paper on a desk remains dry and
does not attract dirt. Volatile biocide formulations applied with
small droplet sizes have a shorter period of efficacy. There are
formulations available to prolong the efficacy of such active
ingredients (eg: encapsulated formulations).
• OUTDOOR ADULT MOSQUITOES:
These types live near their breeding habitat in shadowy and
humid areas, where they rest during the day. While indoor
treatments require “dry” fog with ultra-fine droplets to avoid
stains on sensitive surfaces, outdoor applications against flying
mosquitoes require slightly larger droplets up to 20 µm, which
are less sensitive to air dispersal, less volatile and which ideally
should carry in every droplet volume the lethal dose for one
mosquito. Fogging equipment provides the appropriate nozzle
sizes to produce these larger droplets.
(Source: Information on Adult mosquito control courtesy of pulsFOG)
3 EQUIPMENT
There are several different types of application equipment. A short
summary of the three types of applicators follows:
1. ROTARY DROPLET GENERATORS:
2.AIR-SHEAR DROPLET GENERATOR:
This generator makes use of a disk or mesh cage, revolving at
high speed. The liquid flows from the centre to the periphery of
the rotating surface, where it is discharged to form small droplets
through the action of aerodynamic forces of the surrounding air.
The air-shear nozzle creates the droplets by passing the liquid in a
very thin film over a surface. The wind, created by the blower, and
the rotation of the disk, will shear the droplets off from the liquid
at the edge of the disk.
Wire mesh gauze
produces spray droplets
AIR FROM MISTBLOWER
Adjustable fan blades
determine speed and droplet size
This picture, of a Rotary Droplet Generator, represents the side view of a
spinning nozzle and the strings of liquid coming through the small holes in
the sleeve, breaking up into small droplets.
The picture above shows the droplets from an air-shear droplet generator.
3.THERMAL FOGGERS
All thermal fogging machines were originally developed for the
application of oil-based fogging mixtures for vector and pest control
measures. Following this, they were adapted for plant protection
use in greenhouses, as well as outdoors on agricultural crops.
A thermal fogger is a device that uses the hot exhaust gas
of the engine as the mechanism to produce a fog without
degrading the active ingredient.
Thermal foggers using oil-based products produce a range of
droplet sizes including a large number of very small droplets.
A spectrum of droplets is generated between 0 - 40 µm, with
80 to 90 % of all droplets in a range of 10 to 25 µm depending
of the nozzle size and the formulation used, e.g. low viscosity
formulationsu. The “highly visible fog” is only produced when
oil based products such as diesel fuel or kerosene are mixed
as a carrier for the pesticide, or if water based products with a
minimum content of 30% glycol is used.
In cases where water based chemical preparations are used,
they have to be mixed with clean water. The fog produced
from water based formulations is not very visible and can be
compared with the fog of a ULV space spray applicator. The
Street fogging (vector control)
increased visibility of the fogging cloud can help the operator to
monitor the fog and ensure thoroughness of application. There
are many types and brands of thermal fogging machines on the
market. The first brands were created in Germany and USA at
the end of World War II.
Thermal aerosol fog applicators generally use lower concentration
than ULV or cold foggers. The use of greater volumes of fog is to
ensure the correct active ingredient amount is dispersed in the
designated area. The same actual amount of active ingredient
per unit area is used irrespective of whether it is cold or hot
fogging. Applications can be made from a vehicle, or by a manual
operator. It is recommended that a rate of 1.5 - 2.0 litres of carrier
oil/ha or a dilution concentration of less than 5% for the control
of mosquitoes and other small flying insects. The ULV spraying is
a mixture of mineral oil and a specially formulated insecticide of
higher concentration to make it possible to use less total product
mixture in each application.
As already previously mentioned the ULV fogging generators are
generally vehicle-mounted, in order to cover a large area within a
limited time frame.
Water based fog in greenhouses
Fogging Bacillus thuringiensis on oil-palms using
BIO technology
ULV cold fogging machine using pre-formulated oil-based or water based pesticides for vector control.
These machine types are generally very expensive due to the fact that an 18 hp 4-stroke engine, a high
performance air compressor and a chemical resistant metering pump are required
Source: pulsFOG (all above photos)
Footnote:
uViscosity: Resistance of a fluid to flow. (refer to page 26)
4THERMAL FOGGERS V’S
COLD FOGGERS (ULV)
Both of these devices can be effective in mosquito control and meet ULV standards: application quantity less than 5 litres/ha with a
corresponding droplet range up to 50 µm. As previously mentioned a desirable VMD should be between 8 to 15 µm.
Table 1. Comparison between Cold Fog, (ULV) and Thermal Fog spectrums
THERMAL FOG GENERATORS
COLD FOG GENERATORS
Advantages
Advantages
• Short application time due to higher flow rate (L/hour)
• No traffic hazards because fog cloud is nearly invisible
• Dense, visible fog, therefore perfect observation of fog
distribution and fog drift
• Little or no quantities of carrier substances
• Lower concentration of the active ingredient
• Therefore reduced volume of output (L/ha, but not of
active ingredient)
• Psychological effect on people (something is happening)
• Little or no smell caused by carrier substances
• People can escape direct contact with the fog cloud
• Lower noise level
Disadvantages
Disadvantages
• Cost of carrier substances
• Strong smell of oily carrier substances, where diesel fuel is
used as a carrier. Where kerosene or white mineral oil is used
as a carrier there is no smell (except for any odour associated
with the pesticide used)
• Possible traffic hazards through dense fog
• High noise level of the machines
• Operation requires some experience
• Requires longer application time
• Fog is hardly visible, therefore observation of fog distribution
and fog drift is difficult
• People cannot easily avoid the fog cloud
• Lesser psychological effect (nothing can be seen)
• Higher concentration of active ingredient
(Source: Swingtec)
Thermal fogging consists of a mixture of between 1.5 - 2 litres max
of diesel or kerosene/ha plus insecticide. The formulating dose
will depend of the type of insecticide used, and the dosage rate as
per the label. In most cases between 3 to 5% of the volume will
be the insecticide formulation. ULV spaying is a mixture of mineral
oil and a specially formulated insecticide.
Until recently, the use of diesel oil or kerosene was the traditional
method for thermal fogging as well as for ULV space spraying.
However with the increasing need to reduce environmental
contamination with hydrocarbon solvents, and also to reduce a
possible fire hazard in hot climates, the use of water or of a water/
oil-emulsion as a fogging carrier should be given preference in
thermal and cold fogging.
Note: Table 1 discusses a number of generalised comparisons between ULV (Cold fogging) versus Thermal fogging. There are always exceptions to general observations
and experienced operators will note:
1. Thermal fogging generators do require a higher output (combined volume
3. Under certain conditions, ULV operations can be conducted much quicker
of insecticide plus the carrier).
than Thermal fogging operations. Speeds of up to 36 Kph may be possible
for ULV machines under some conditions. With Thermal fogging, a speed of
2. As the result from a Thermal fogging generator is immediately visible
8 Kph is rarely exceeded.
(fog cloud), this can result in a tendency to speed up the application by
Source: Personal Communication: Practical Vector Control, USA.
inexperienced operators and thus under apply the insecticide.
ULV spraying, where diesel fuel is not used as the carrier, may
be relatively more environmentally friendly, as well as safer,
than thermal fogging.
However, ULV applications may be somewhat less effective
in heavy vegetation than thermal fogs because of reduced
penetration due to the larger droplets. Control of the droplet size
is important to insure proper drift and to prevent car spotting,
which can occur with some insecticides due to the corrosive
properties of the undiluted active ingredient in larger droplets.
There are major differences between the vehicle mounted
and portable applicators.
For example:
The capacity of the combustion chamber in portable thermal
foggers ranges between 13-19 kWu (approx. 17-25 hpv) whereas
the capacity portable cold fogging ULV applicators is normally
under 1.5 kW (approx. 2 hp).
In motor vehicle mounted devices, performance ranges between
35-75 kW (approx. 47-101 hp) for thermal foggers and between
6-13 kW (approx. 8-18 hp) for cold foggers. The output capacity
and the ability to produce a correct spectrum of ULV droplets (<30
µm) is directly dependent on the power of the output machine
and the formulation characteristic of the used pesticide. In
particular the nozzle efficiency determines the amount that can be
properly atomised. Thus the output of droplets ranging less than
30 µm is: Approx 3 litres/hour with portable cold foggers, up to 25
litres/hour for vehicle mounted cold foggers (ULV); and with up to
more than 100 litres/hour vehicle mounted thermal foggers.
Note: Adjustments for appropriate vehicle speeds has to be
adapted, and for the pesticide concentration need to be considered.
Notes on conversions:
The performance data, kilocalories, kilowatt and horsepower
are calculated from the fuel consumption of a thermal fogging
machine including the loss of radiated heat energy, based on
physical formulas.
As an example we can take a thermal fogger having a fuel
consumption of two litres per hour.
The medium calorific value of fuel is 8,050 kcal per litre = 16,100
kcal per hour to be divided by 860w = 18. 7 kW
For the conversion into horsepower, kW has to be multiplied by 1.36
For this calculation it will be 18.7 kW x 1.36 = 25.4 hp.
(Source: Swingtec)
Footnote:
u kW: kilowatt is equal to one thousand (103) watts and indicate the output power of an engine
v = Horse Power
w kcal: kilocalories 1 kcal = 0.001163 kWhrs. = 859.845227859 x kcal = 860 kWhrs.
5 DROPLET LIFE SPAN
1. DROPLET EVAPORATION CONSIDERATIONS
It is important to understand that the effectiveness of a pesticide
is influenced by the size of the droplets and the equipment that
is used for the application. The smaller the target (insect), the
smaller the droplet size required.
Water droplets evaporate completely in a couple of seconds
depending on the temperature as well as the relative humidity.
If the droplets of ULV fog were to behave in a similar way, the
application would be completely ineffective. It is important to
keep the aerosol droplets active as long as possible so they can do
a perfect job.
When a drop of water falls on a hot surface it dances for a long
time before evaporating quickly. This is a result of the creation of
a fine vapour layer that surrounds the droplet upon encountering
such heat. This vapour layer acts to insulate the droplet from
further evaporation.
Water droplets evaporating
2.EQUIPMENT DEVELOPMENTS IN THE APPLICATION OF WATER-BASED MIXTURES
Most ULV formulations are oil based and contain additives which
greatly inhibit evaporationu. Certain additives can increase this
effect significantly, thus preventing the evaporation of even the
smallest aerosol droplets for a longer period. For water based
formulations, a glycol component will do the same job like the oil
component for oil based formulations. Using a glycol component
as an evaporation inhibitor may require the addition of a 3%
surfactantv to some formulations. (eg: any biodegradable non
ionic surfactant is suitable)w.
There is almost no difference when water-based chemical
mixtures are applied with a ULV fog generator. However things
are completely different when water-based chemical formulations
are applied with a thermal fog generator, because of the
higher surface tensionx of water; hence the need for the High
Performance Fogging Tubes.
For environmental reasons, water-based ULV formulations
have become more available over the last few years. These
formulations contain substances which prohibit rapid evaporation.
All droplets which are larger than 50 µm will not remain airborne
and quickly fall to the soil in the immediate area surrounding the
applicator. Up to 30% of the fogging liquid could be deposited
in the immediate vicinity of the fogging machine. Thus is wasted
(refer following photos).
With standard thermal fog applicators, the droplet spectrum varies
from very small droplets up to large droplets of 200 µm and
more, dependent to the dosing nozzle installed.
Footnote:
u Evaporation is the conversion of the liquid into a vapour or a gas.
vSurfactant is an abbreviation for SURFace ACTive AgenT. These are used to help in the creation of correct droplet sizes and in improving penetration
and spread of the product on to the vector.
wDifferent countries would use different trade names. Please check the label for appropriate biodegradeable non ionic surfactant available in the
country of operation. These products are used as aides in dispersing the active ingredient.
xSurface tension is a natural phenomenon that prevents the even spreading of a water based pesticide formulation on a target organism or surface.
Surfactants are used to minimize surface tension.
Nozzle 1.2, 50 Seconds
The reasons for such losses are due to:
• the size of nozzle used in the fogging machine;
• all thermal fogging machines are not capable of handling high
output quantities of water-based fogging mixtures to form a
suitable droplet type.
• the much higher surface tension of water compared with the
surface tension of oil (diesel oil or kerosene).
The result is that the large droplets do not remain airborne for a
long time.
As already mentioned, when water-based mixtures are applied
with a standard thermal fogging machine, droplets in a range
between 0 and 200 ++ µm with a rather large portion of large
droplets are generated. Unfortunately large droplets, which are
too heavy, do not remain airborne for a sufficient period of
time to be effective in controlling the vector. Depending on flow
Nozzle 1.2, Detail 120 Seconds
rate between 20 to 30 % of the fogging mixture (and the active
ingredient) are lost and wasted. The only way to avoid those kinds
of losses is by the use of a High Performance Fogging Tube.
The High Performance Fogging Tube was specifically designed for
the application of water-based fogging mixtures. With this piece
of equipment, an excellent droplet spectrum is achieved with
no large droplets. The droplet spectrum is comparable with that
achieved with oil-based fogging mixtures.
The wide droplet spectrum which is generated by all standard
fogging machines when using water based mixtures, does not
meet WHO specifications (< 30 µm VMD). These specifications
can be met with Swingfog machines equipped with the Swingtec
high performance tube. eg: The Swingfog SN50 with the high
performance tube will achieve the correct spectrum with water
based chemical mixtures when used at a flow rate of up to 27 L/hr.
(Source: Swingtec)
3.FORMULATION DEVELOPMENTS IN WATER-BASED MIXTURES
With the exception of a few chemical formulations, such as
the Bayer Products Aqua Reslin®, Aqua K-Othrin®, and Aqua
Py®, most water-based pesticide preparations do not contain
an anti-evaporation agent. When such chemical formulations
are applied it is a must that an anti-evaporation agent (such as
10% glycol accompanied with 2-3% biodegradable non ionic
surfactant) is added to the total mixture. The use of an innovative
spray technology called FFAST (Film Forming Aqueous Spray
Technology) which reduced the need for use of solvents in space
spraying application. FFAST formulations are primarily waterbased, are diluted with water and achieve optimal efficacy. These
formulations are now widely used in many countries.
That refers as well to thermal and ULV space spray applicators.
The amount of anti-evaporation agent should be no less than 5%
of the total fogging mixture. Under conditions of high temperature
and low relative humidity, this amount has to be increased up
to 10%. The anti-evaporation agent ensures that the tiny aerosol
droplets will not evaporate too quickly and that the life span of the
droplet is considerably extended.
In thermal fogging generators, the anti-evaporation agent will also
slightly increase the visibility of the water-based fog. By adding more
than 10% (up to 30%) of an anti-evaporation agent, a good visible
fog cloud can be achieved. The use of more anti-evaporation agent
will not improving the result of the application, but will improve the
visibility and the lifespan of the fog.
Refer to Annex 3 for a detailed explanation on the
determination of droplet sizes.
(Source: Bayer Towards Sustainable Vector Control)
STAGES IN THE FORMATION OF A STABLE ‘AQUA’ DROPLET Extracted from Bayer Publication ‘Aqua-K-Othrine’ (2010)
STAGE 1
STAGE 2
Continuous
aqueous phase
Rapid
evaporation
of water
Rapid
evaporation
of water
Continuous
aqueous phase
Oil phase
Oil phase
STAGE 3
STAGE 4
Evaporation of water
at reduced rate
Long chain alcohol
forms a complete
stable film at the
droplet surface
Migration of long
chain alcohol
forming a stable film
at the surface
Surface film comprising closely packed long chain alcohol
molecules hindering the diffusion of water molecules
OH group
Hydrocarbon tail
Time scale from atomination to
surface film formation: < 1 second
Table 2. Some examples of FFAST formulations (from Bayer)
PRODUCT
ACTIVE INGREDIENT
CHEMICAL CLASS
FORMULATION RATE OF ACTIVE
INGREDIENT*
Aqua Reslin Super
Permethrin, Piperonyl
butoxide, S-bioallethrin
Pyrethroid
Refer specific label directions for the relevant area
Aqua K-Orthrine
Deltamethrin
Pyrethroid
0.5 - 1.0 g ai/ha
* Note that this rate may vary according to the country of registration and use.
Extracted from Leading water-based space-spray technology for the control of mosquitoes and flies, 0410 Edition ©2010 Bayer Environmental Science
6THERMAL FOGGERS AND
OPERATING TEMPERATURES
It is often suggested that in thermal fogging, the temperature of
the hot gas flow or “the open flame” destroys a portion of the
active ingredient. This is not the case with high-quality devices
which have been properly adjusted and certified by WHO
Cooperation Centres.
With a correctly adjusted quality device, fuel combustion should
take place in the combustion chamber in the back section of the
resonator achieving nearly 100% combustion. The flame should
end in the middle section of the resonator tube and should never
reach to the point where the fogging mixture is injected. In some
foggers, the fog solution socket (nozzle) is not installed at the end
of the resonator tube, but considerably closer to the combustion
chamber. pulsFOG offers both versions: injection at the end of
resonator (for the use of wettable powders (WP)u in greenhouses)
and in a hotter area nearer to the combustion chamber (for the
use of all other water-based and oil-based pesticides). The result
is a better use of the exhaust energy leading to a narrower angle
of droplet spectrum and providing a higher flow rate when using
the injection point in a hotter area. The use of WP formulations
with a thermal fogger causes blockages or choking problems if the
distance between the injection point and the end of the resonator
is too far apart.
The time that the insecticide is injected in the hot gas flow, and
the time that the insecticide is transformed into fog is very short
(according to a research report of the university of Berlin: 0.05 to
0.1 seconds), so that there is no chance to destroy the insecticide.
This is very important and a question which is always raised by
people with little knowledge on how a thermal fogger works.
SHUT-OFF DEVICE:
It is recommended that all thermal foggers which make use
of combustible preparations be fitted with an automatic
formulation shut-off device. Should the machine be incorrectly
used or stop unexpectedly due to lack of fuel, the shut-off
device prevents the pressure in the chemical tank from feeding
the fluid into the extremely hot combustion chamber, where it
could ignite (fire hazard).
Restriction nozzle
conduit
valve
Chemical tank
pulsFOG automatic shut off device: heat, acid and chemical resistant
The following pictures show some automatic cut-off devices on some fogging machines.
Automatic cut-off device for the fogging mixture by
means of an electro-magnetic valve
Automatic mechanically acting cut-off device for
the fogging mixture
(Source: Swingtec)
(Source: Swingtec)
Footnote:
Automatic cut-off valve as a safety device
for the application of inflammable fogging
solutions with the thermal fogger
(Source: pulsFOG)
uWettable powders (WP)
Table 3. Insecticides used for cold aerosol or thermal fog application against mosquitoes
INSECTICIDE
CHEMICAL
DOSAGE OF ACTIVE
INGREDIENT(g/Ha)
COLD AEROSOLS
THERMAL
FOGS
WHO HAZARD
CLASSIFICATION OF
ACTIVE INGREDIENT
Fenitrothion
Organophosphate
250-300
250-300
II
Malathion
Organophosphate
112-600
500-600
III
Pirimiphos-methyl
Organophosphate
230-330
180-200
III
Bioresmethrin
Pyrethroid
5
10
U
Cyfluthrin
Pyrethroid
1-2
1-2
II
Cypermethrin
Pyrethroid
1-3
-
II
Cyphenothrin
Pyrethroid
2-5
5-10
II
d,d-transCyphenothrin
Pyrethroid
1-2
2.5-5
NA
Deltamethrin
Pyrethroid
0.5-1.0
0.5-1.0
II
D-Phenothrin
Pyrethroid
5-20
-
U
Etofenprox
Pyrethroid
10-20
10-20
U
LambdaCyhalothrin
Pyrethroid
1.0
1.0
II
Permethrin
Pyrethroid
5
10
II
Resmethrin
Pyrethroid
2-4
4
III
Notes:
Class II - Moderately hazardous class
Class III - Slightly hazardous class
U - Unlikely to be an acute hazard under normal usage
NA - Not applicable
Source: Extracted from several WHO publications.
7PROCEDURE, TIMING AND
FREQUENCY FOR THERMAL
FOGGING AND ULV SPACE
SPRAY OPERATIONS
BASIC STEPS:
The objective is to spray in the vicinity of all houses, animal shelters
and covered drains along open roads and foot paths in the selected
area (all areas where mosquito vectors are likely to be present).
Droplets drift ten or more meters downwind, depending on
obstacles in their way. The following steps are recommended in
carrying out the space spraying of the designated area:
• The street maps of the area to be treated must be studied
carefully before the fogging operation begins; (prior planning is
critical to the success of a fogging program).
• The area covered should be within a radius of at least 400 to 500
meters from the house where the dengue/malaria case was located.
• Residents should be warned in advance before the operations
so that food is covered, fires extinguished, and pets are moved
out together with the occupants.
• Ensure proper traffic control when conducting outdoor
thermal fogging, since it can pose a traffic hazard to motorists
and pedestrians.
• Wind force and down wind speed is especially important for
making the most of air currents for the distribution of fog.
Street fogging. Source: pulsFOG
The following Table 4 lists various wind forces and their
corresponding wind speeds in keeping with the Beaufort scale.
The observation of visible signs in the area contributes to the
correct evaluation of wind conditions. Effective swath widths,
which depend on wind speed, are also listed. Swath width is
particularly crucial for calculating and adjusting the output (litres/
hour) of the device and walking or driving speed.
No wind, or low wind speeds only allow for small swath widths
up to 50 m. At a wind force of 2 or 3 (up to 20 km/h), greater
swaths of up to 150 m and even more are possible. Better
saturation of vegetation and higher impact also result. This is
especially desirable for the contact effect of flying pests in adult
vector control.
Table 4. Application in open space (Wind force /wind direction/swath width)
WIND
FORCE
DESCRIPTION OBSERVATIONS
Force 0
Force 1
Force 2
Force 3
calm
light draft
light breeze
soft breeze
Force 4
smoke rises vertically
observable drift of smoke
rustle of leaves
leaves and twigs are moving
constantly
Moderate breeze movement of small branches,
whirl of dust and paper
WIND SPEED
m/s
0.0 – 0.2
0.3 – 1.5
1.6 – 3.3
3.4 – 5.4
km/h
0.0 – 0.7
1.1 – 5.4
5.8 – 11.9
12.2 – 19.4
5.5 – 7.9
19.8 – 28.4
EFFECTIVE SWATH WIDTH / IN mu
ULV
25 -50
35 - 70
50 - 100
75 - 150
ULV - Plus
20 -40
25 - 50
35 - 70
50 - 100
LV
15 - 30
20 - 40
25 -50
30 - 60
Application possible with certain
reservationsv
Fogging in sewage plant. (Photo source: Swingtec).
Fogging should always be conducted travelling across the wind
from downwind to upwind i.e. preventing the spray operator from
being in the fog as much as possible.
Photograph above; fogging technique with vehicle mounted fog
applicator will give the reader a clear indication on how fogging
should be conducted.
Footnote
u Effective swath width = total swath width / overlap (approx. 30%)
vApplication is only recommended under certain conditions at wind force 4, as the fog clouds swirl too strongly, reducing their effectiveness. Should
application nevertheless take place under less than ideal conditions, a higher total application volume (more carrier substances with the same
amount of active ingredient) must be used and walking or driving speed reduced to compensate for the lower concentration of the active ingredient.
8VEHICLE-MOUNTED FOG
APPLICATION WITH THERMAL
FOG GENERATORS OR ULV
SPACE SPRAY APPLICATORS
As already mentioned in a previous chapter those generators/
applicators are used to treat large spaces.
With thermal foggers and with genuine ULV backpack space
applicators, as well as with truck mounted ULV fogging generators
an effective swath width of at least 40/50 meters can be obtained.
With a little wind assistance swath widths of up to 100 meters
can be achieved (refer to table 4). Fogs are dispersed as aerosols
through thermal fog or ultra-low volume sprayers (cold foggers).
Because of the small size, these aerosols generally are not suitable
for the distribution of Larvicidesu.
However they are very effective for flying insect control, because
the individual droplets do not settle to the ground rapidly.
Temperature inversion helps to hold the material below the
upper, warmer thermal layer of air and consistent light wind (8
to 16 km/h) serves as a propellant, which propels the through
the habitat.
Those generators, used in mosquito control programs, produce an
insecticide fog that moves across open spaces, killing mosquitoes
in flight, as air currents move the fog cloud. Thermal fogging
requires a large vehicle to accommodate the volume of diesel
that will be mixed with the insecticide. The maximum road speed
is between 8 and 15 km/h. Because of the high cost and possible
environmental impact of the petroleum products, used in thermal
fog application, the popularity of thermal fogging with oil has
changed in recent years.
FOGGING TECHNIQUE:
Doors and windows of houses and buildings in the area to be
sprayed should be opened.
Recommendations for vehicle fogging:
• The vehicle is driven at a steady speed of 8-15 km/hr along
the streets. Spray production should be turned off when the
vehicle is stationary.
Street fogging. Source: pulsFOG
Footnote:
u Thermal fogging machines with a special design (pulsFOG BIO) provide the necessary larger droplet spectrum for larvicides such as Bacillus
thuringiensis var.israelensis
• Always spray downwind to upwind. If possible, drive the
vehicle at right angles to the wind direction. In areas where
streets run parallel as well as perpendicular to the wind
direction, fogging is only done when the vehicle travels
upwind in roads parallel to the wind direction.
• In areas with wide streets with houses and buildings far
from the roadside, the spray head should point at an angle
to the left side of the vehicle (in countries where driving is
on the left side of the road) or on the right side (in countries
where driving is on the right side of the road). The vehicle
should also be driven close to the edge of the road. Some
people neglect this suggestion, thinking that it’s enough that
the wind moves the droplets.
• In areas where the roads are narrow, with houses close
to the roadside, the spray head should be pointed directly
towards the back of the vehicle.
• Driving into dead-end roads, the fogging is done only when
the vehicle is driving out of the dead-end, not while going in.
• The spray head should be pointed at a 45° angle to the
horizontal to achieve maximum throw of the droplets (only
with ULV machines).
• Vector mortality downwind increases as more streets are
sprayed upwind in relation to the target area.
Figure 1.
OVERLAPPING SWATHS
Diagram illustrating how to apply
an insecticide fog to control
adult mosquitoes in a target
area. (Swath should be 60 to
150 meters wide with about a 30
meter overlap.)
Resume
fogging
Swath 4
Stop
fogging
Resume
fogging
Swath 3
Stop
fogging
Swath 2
Swath 1
Target Area for
Adult Mosquito
Control
Always direct the fog to go with
the wind direction.
Resume
fogging
End of fogging
operation
Approximately
150 meters
Start of fogging
operation
Wind direction
velocity under 6 km/hour
(4 mph)
Stop
fogging
Resume
fogging
Stop
fogging
Approximately 300 meters
CALCULATING THE OUTPUT RATE:
The device’s flow rate in litres/hour is determinate by following parameters:
• Speed of the vehicle (1.0 km/hour = 1,000 m/hour).
• Effective swath width according to Table 4 (in meters).
• Quantity of the chemical formulation as per manufacturer label (litre/hectare = litre/10,000 m2) including any carrier substances.
It is calculated using the following formula:
Speed (meter/hour) x Swath Width (meters) x Quantity (litres/hectare) = Output amount to be set at the flow meter (L/hr)
For example:
Driving speed:
10 km/hour = 10,000 m/hour
Effective swath width:
50 m
Dosage:
0.5 L/ha (L /10,000 m )
10,000 m x 50 m x 0.5 L
50 x 0.5 L
=
1.0 ha x 10,000 m hr
2
2
=
25 L/hr
The calculation shown above is typical for the application of an undiluted chemical formulation used in ULV mode.
(Source: Swingtec)
Hint:
If formulations are to be applied with carrier substances, the quantity of the additional carrier substance is to be added to the quantity of
formulation. Quantity of chemical formulation needed in accordance with the manufacturer’s label (L/ha) + quantity of carrier substance
(L/ha) = total chemical preparation (L/ha)
Table 5. Comparison of backpack mist blower and vehicle mounted ULV ground equipment
OPERATIONAL CONSIDERATIONS VEHICLE MOUNTED ULV
BACKPACK MIST BLOWER
Performance per day of 4 hours
• 16 km/h or 16,000 m/h
• 64,000 m per 4 hours per day
• 3 minutes per house or 20 houses/
hour/team of 3 sprayers
• 80 per 4 hours/day/machine/team
Swath
• 150 meters swath width
• 10 meters swath width
Optimum droplet size
• 20 µm
• More droplet density
• Same as vehicle mounted ULV
equipment
Safety to the operators
• Only 2-3 operators, less handling of
concentrate
• More work
• 40 machines x 3 man team
Cost
• Equipment cost
• 2-3 spray men to operate
• Vehicle cost
• Cost of 40 machines and 120 spray men
Insecticide droplet
• Poor penetration to reach most indoor
resting sites
• Better penetration
• Likely to reach indoor target sites
(Source: WHO/WPRO)
DETERMINING DRIVING SPEED:
It is rarely possible to maintain a constant vehicle speed, which result in an over-dosage of chemicals when the vehicle is moving slower
than required and an under-dosage when it is moving too fast. Some new spray generators contain a sophisticated metering system having
a flow rate per kilometre calculation which automatically adjusts the output of the insecticide. When the vehicle has stopped, fogging
will stop. When the speed of the vehicle increases, the output will increase and when the speed is reduced, the output will be reduced
automatically. An application in L/km compensates the variations of the speed and guarantees always the correct output and coverage.
The driving speed can be calculated as follows:
• Effective swath width according to Table 4 (in meters).
• Quantity of the chemical formulation according to manufacturer’s label in Litres per hectare including any carrier substances
• Area (in m2)
• Output rate (in litre/hour)
The following formula is used:
Area (m2) x Output rate (litre/hour)
=
Quantity per ha (L) x Swath Width (m)
Driving speed (km/hour)
For example:
Area:
10,000 m2
50 m
Quantity per ha:
0.5 L/ha
Output rate:
25 litres/hour
10,000 m2 x 25 L
250,000 m =
= 10,000 m/hr = 10 km/hr
0.5 L x 50 m x hr
25 L/hr
(Source: Examples supplied by Swingtec).
HOW TO CALCULATE THE DAILY TREATMENT DETAILS USING VEHICLE MOUNTED ULV GROUND
FOGGING EQUIPMENT
Calculate the sprayed areas as Hectares treated:
• If vehicle speed = 8 kph (as an example).
• Then 8 km x 1,000 m = 8,000 m per hour
• 8,000 m x 100 m swath width = 800,000 m2 per hour
• Let 10,000 m2 = 1 ha
• 800,000 m2 divided by 10,000 = 80 ha x 4 hours of operation/day = 320 ha/day.
Insecticide Required:
• If flow rate = 88.7 mL/minute. (This example is based on a flow rate of 3 US fluid ounces per minute = 3 x 29.57 mL = 88.7 mL).
Then one hour of operation: 60 minutes x 88.7 mL = 5,322 mL per hour.
• For one day of operation, 4 hours x 5,322 mL (or 5.3 litres) = 21.29 litres of formulated insecticide.
(Source: WHO/WPRO)
Volume:
3 US Fluid Ounce
Time:
60 min
Hours worked per day:
4 hr
Note:
US Fluid Ounce
=
Imperial Fluid Ounce =
3 Fl Oz x 29.57 mL x 60 min x 4 hr 21.29 L
=
1000 mL
29.57 mL
28.4 mL
9PORTABLE THERMAL
FOGGING
A SHORT HISTORY OF PORTABLE FOGGING UNITSu
The development of the technology goes way back to the beginning of last century.
A Chronicle of the Pulse-Jet Resonator Engine (brief Translation of German publication in 1948*)
The first functional pulse-jet built by Caravodine in 1906 and Marconi in 1908 (Wikipedia) is an aero resonator jet having neither piston
nor crankshaft and is referred to simply as a “stovepipe”. Its front end is closed off by moving flaps (valves). Petrol injected into the pipe
combusts rhythmically at a rate of 50-100 explosions per second. The combustion gas generates thrust as it streams out. The Germans,
P. Schmidt and Reynst, continued the development of Marconnet’s resonator in the 1930’s. A steam generator was also proposed. In
1941 the inventor Dr. Gunther Dietrich finds the key to improving the starting and running characteristics of the engine culminating in the
series-production of a simple jet engine: The first automatically controlled cruise missile launched in great numbers in World War II. This jet
engine is also manufactured in Friedrichshafen and Überlingen on Lake Constance until the factories were destroyed by Allied air raids.
Flap valve
Air
intake
Fuel tank under pressure
Spark plug
Air pressure bottle
Combustion
Fuel
1941 DIEDRICH-ARGUS:
Aero Resonator
Air intake
1941 DIEDRICH: Resonator
Dampfaustritt
Brennstoff
Zundkerze
Uberleitungsrohr
Luft
1909 MARCONNET:
Resonator Modellgerat ohne Einlaßventil
Abdeckblech
Example of a combustion chamber without
diaphram for the control of air intake
Gasverteilring
Venturitrichter
Luft
Gas
Luft
Wassermantel
Wassereintritt
Vergaser
Zundkerze
1930 REYNST:
Resonator Verpuffungstopf als Dampferzeuger
Luft
Brennstoff
1909 MARCONNET:
Resonator Modellgerat mit Einlaßventil und Vergaser
Example of a combustion chamber with
controlled air intake using a diaphram
u (Source: History and pictures of basic fogging unit operation, provided by pulsFOG.)
The first thermal fog generator to reach the market was a
Swingfog which was using the engine principle of the first cruise
missile, the V-1.
All other thermal fog generators which are nowadays available in the
world market are originating from this basic invention. Shortly after
the basic invention, with Dyna-Fog, USA a second thermal fogging
machine was introduced, using the same engine principle. Later on,
1968 Dr. Stahl founded the trademark pulsFOG with new patents for
the starting device. In 1982 Igeba was founded by a former salesman
of Swingfog.
Those four above mentioned brands, were the only products
playing a role on the world market for many years. In recent years,
some thermal fogging machines, mainly originating from Korea
and China were introduced, but these machines have had little
international usage to date.
FOGGING TECHNIQUE - PORTABLE FOGGERS:
As already mentioned in a previous chapter those generators/
applicators are used to treat smaller, more confined areas.
Doors and windows of houses and buildings in the area to be
sprayed should be opened.
The techniques recommended for portable fogging are principally
the same as those for vehicle mounted foggers detailed in chapter 8.
There will be, of course, considerations given to the smaller scale
of the operation.
• Do not enter the house. House fogging, is fogging in the
vicinity of the house, the exterior surfaces of the house as
well as under the house and eaves.
• Stand three to five meters in front of house and spray for
10 to 15 seconds directing nozzle towards all open doors,
windows and eaves. If any side of the house is longer than
about 20 meters, the spray operator will have to move over
about 10 meters and spray from two positions on the same
side of the house. If appropriate, turn away from house and
standing the same place, spray the surrounding vegetation
First experimental fogging device (in 1947) using pulse jet engine.
First prototype of a pulse jet thermal fogger 1948 launched by Dr. Stahl
(Co-founder of Swingtec in Überlingen/Germany)
for 10 to 15 seconds. Proceed to left, rear and side of the
house and repeat as above.
• If it is not possible to stand 3 meters from the house due
to closeness of houses and lack of spray space, nozzle
should be directed towards house openings, narrow
spaces and upwards.
• While walking from house to house hold nozzle upwards so
that particles can drift through. Do not hold nozzle towards
ground. This to avoid direct contamination of the soil.
• Spray particles drift through the area and into houses to kill
mosquitoes which become irritated and fly into the particles.
The settled deposits can be residual for several days to kill
mosquitoes resting inside houses and on vegetation not
exposed to the rain.
• This technique permits treatment of a house with
insecticide ranging from 1 to 25 grams in one minute.
The dosage depends on discharge rate, concentration of
insecticide applied, and time it takes to fog the house.
(Source: WHO/WPHO)
Portable Fogging
Figure 2 Basic design of a thermal fogging machine
Fuel/air mixture
Fogging mixture
Combustion
1000/1100 °C
Inert exhaust
900 °C
800 °C
700 °C
600/550 °C 50/60 °C
(Source: Swingtec)
FUNCTIONING DETAILS:
Some fogging machines run with regular grade petrol/gasoline
(unleaded or leaded). The unit works according the pulse-jet
principle without any mechanical moving parts.
When starting the generator, using the pump the primer or an
electric starting button, a fuel/air mixture is produced in the
carburettor, blown to the combustion chamber and ignited by
a spark plug in the combustion chamber. This action produce a
column of gas in the resonator tube, having 80 to 90 oscillates
(explosions) per second. The action is controlled by an air
diaphragm valve and a fuel adjustable screw in the carburettor.
A small amount of the clean exhaust gas is automatically fed back
into the fuel and spraying tank to build up constant pressure to
convey the fuel into the carburettor and to convey the fogging
mixture to the resonator tube. Electrical energy is requires only for
starting the generator. Once the unit is running, electrical energy
is not needed any longer. The electric energy is supplied by 4 dry
batteries 1.5 V each.
The peak temperature in the combustion chamber is
approximately 1,100°C. The temperature gradually decreased in
the resonator pipe and where the solution is introduced the hot
exhaust gas stream has a temperature of 500 to 550°C only, this
depending on the environmental temperature. When the fogging
solution is injected into the resonator pipe through the solution
nozzle, the liquid absorbs the heat immediately. Each of the tiny
droplets starts to evaporate and thus absorbs the heat, but the
loss by evaporation is quite negligible because each of the tiny
droplets is developing a gaze cover which protects the inside of
the droplet from total evaporation. The liquid partially vaporise
and converts into a visible fog.
The temperature at the entry point of the fogging mixture is
approximately 600-550°C (depending on the carrier substance
and output rate), and this for a dwell time of 4 to 5 milliseconds
only. Temperature in the fog measured just after leaving the
resonator is between 50 and 60°C, and the fog needs only
4 milliseconds to get out of the resonator and is dispersed
into fine aerosol droplets immediately to the environment by
creating a dense fog. For this reason, temperature-sensitive
substances can be used without suffering any damage.
As already mentioned the system has, with the exception of
diaphragms, no moving parts and, therefore, little wear and tear.
The engine will continue to operate as long as fuel is supplied
through the carburettor.
The standard four D size batteries also provide electrical power to
operate the fogging mixture cut-off device. Some manufacturers use
pneumatic energy from the carburettor to operate the cut-off device.
Pneumatic energy is created by a compression force of air, or gas in
a confined space.
Figure 3. Technical Description
Air valve
Pulse-jet engine
Fuel
Quick start carburettor with direct
fuel injection from pulsFOG
Enlarged picture of the combustion chamber (see previous page) showing the carburettor set up.
Adjsutable
direct fuel
injection
1
Double cooling jacket
1200 - 1400 °C
Combustion chamber
Cooling air
intake
pulsFOG BIO system:
Water injection for
pre-cooling and cleaning.
May be used additionally
for pesticide injection to
increase the unit output
or flow rate
1000 °C
500 °C
Resonator (exhaust pipe)
2
1200 - 1400 °C
1000 °C
500 °C
3
1200 - 1400 °C
1000 °C
500 °C
Summary of different features in fogging machines.
1.pulsFOG BIO: Two injection points of the fogging liquid in
series allow the separated supply of pesticide and carrier liquid
with the aim to combine both liquids at the end (outlet) of
the resonator. The separate carrier liquid (e.g. water) is heat
resistant and absorbs most of the produced heat energy
resulting to a very even droplet spectrum. The pesticide is
parallel injected at the end of resonator and confronted with a
much lower temperature leading to the following features:
•Heavier droplets with a regular droplet spectrum can be
produced for the application of larvicides.
•The separately injected carrier liquid has a cleaning effect and
avoids choking and blocking of the outlet.
•Elimination of any fire hazard with oil-based fogging solutions
even under unexpected conditions.
2.Model for Applying WP Formulations: With the fogging
injection point at the end of exhaust pipe it will retard
choking and clogging with wettable powder formulations is
100 °C
Venturi effect
attracts cooling air
Carburettor with diaphragm
air intake valve
Pesticide injection
Figure 4. Schematic diagram showing basic features of three different fogging machine models
40 °C
Mixing area
60 °C
100 °C
60 °C
avoided. These types are used for plant protection purposes
in greenhouses. Only non-inflammable water-based fogging
liquids are allowed to use.
3.Model for Applying Oil-Based Formulations: With an
injection point towards the middle of the resonator provide
more heat energy for the fogging process with the aim to
produce an extremely dry fog (droplets <15 µmu). These
units are designed to avoid ignition of combustible liquids
with a flash-point > 70°v and are preferred for the use with
oil based formulations and indoor disinfectants (eg Formalin).
ADVANTAGES:
With a minimum quantity of chemical preparation, an optimal
coverage is achieved. In comparison, the portable thermal foggers
with conventional methods achieve approximately 90% labour
savings when treating small areas. There is no soil contamination
by dripping losses and any chemical residues are reduced.
Footnote:
u < = smaller than; > = larger than.
v Flash point of a volatile material is the lowest temperature at which it can vaporize to form an ignitable mixture in air. It is a measure of flammability
measured under strict laboratory conditions.
FOGGING TECHNIQUE:
• Thermal fogging with portable thermal foggers is done from house to house, always fogging from downwind to upwind.
• All windows and doors should be shut for half an hour after the fogging to ensure good penetration of the fog and maximum
destruction of the target mosquitoes.
• In single story houses, fogging can be done from the front door or through an open window without having to enter every room
of the house provided that adequate dispersal of the insecticide droplets can be achieved. All bedroom doors should be left open
to allow dispersal of the fog throughout the house.
• For large single-story buildings, it may be necessary to apply the fog, room by room, beginning at the back of the building and
working towards the front.
• In multi-story buildings, fogging is carried out from upper floors to the ground floor and from the back of the building to the
front. This ensures that the operator has good visibility along his fogging path.
• When fogging outdoors, it is important to direct the fog at all possible mosquito resting sites, including hedges, covered drains,
bushes, and tree-shaded areas.
• The most effective type of thermal fog for mosquito control is a medium/dry fog, i.e., it should just moisten the hand when the
hand is passed quickly through the fog at a distance setting so that oily deposits on the floor and furniture are reduced to about
2.5 - 3.0 meters in front of the fog tube. Adjust the fog setting so that oily deposits on the floor and furniture are reduced; this is
usually done by reducing the flow rate of formulation.
• It is advisable to shut off all electricity at the master switch, prior to application; this is to avoid any possible electrical problems.
(Source: WHO/WPRO)
Figure 5. Recommendations for manual fogging
techniques
This diagram illustrates how to apply an insecticide fog to control
adult mosquitoes in a target area. Swarth width should be 40 m
wide. Always direct the fog to go with the wind direction.
< 10 m > Swarth width
Wind direction
Direction of travel
Source: Swingtec
Start fogging
FREQUENT ASKED QUESTIONS:
Q 1)
Is it possible to use heat sensitive chemicals with
thermal foggers?
Yes, products such as Bti (Bacillus thuringiensis var. israelensis),
natural pyrethrum, even inhalation vaccines and juvenile
hormones can be applied by a thermal fogger, without the active
ingredient is destroyed, when the fogger is correctly adjusted.
pulsFOG registered the BIO technology as a patent in the 1970’s.
Basic research was done by the Technical University of Berlin.
Benefits of the BIO system?
The basic idea was to inject the pesticide and the water as carrier
into the resonator of the machine separately, so these two
components mix at the point where they are atomized. This has
several advantages for a pulse-jet thermal fogger:
• The water is injected into the resonator, at a point of higher
temperature, and cools down the hot explosion gases to 100°C
(evaporation temperature). The insecticide is injected at the
cooler point of 100°C for a duration of 0. 05 – 0. 1 second.
This leads to an even lower temperature, about 40°C, into the
mixing area of “Venturi effect”.u
Footnote:
uVenturi effect is the reduction in fluid pressure that results when fluid flows through a constricted section of the pipe. It is effectively a drop in
pressure caused by moving fluids
• The produced water vapour cleans the resonator exhaust pipe
and avoids residues of the fogging solution at the end of the
pipe. This is advantageous if wettable powder and flowable
formulations have to be used.
• The injection of water avoids any fire hazard. The pulsFOG
BIO technology offers the fogging of highly sensitive active
ingredients, the self-cleaning and the elimination of any fire
hazard with fogging of hazardous liquids.
With this system a heavy wet fog cloud, with a droplet spectrum
< 100 µm with pure water based insecticides, can be produced
and sprayed over water surfaces without loss to the environment
(e.g. Bti products). With the separate water injection the BIO
technology presents a cold fogging application system absolutely
comparable with the expensive ULV machines. Normally thermal
fogging is understood as a limited space treatment against flying
pests, but the BIO system allows as well applications for pests
living near the ground and also on lake surfaces. This is also
important to control the larval stages in wet habitat e.g. in still or
gently flowing water, where no or the least fish are living. Such
control measures need to be well prepared to ascertain exactly
the time period of breeding process.
Q 2)
Is it possible to use the thermal fogger for the
distribution of wettable powder formulations?
Yes, this can be done without having problems of choking and
clogging the outlet of resonator with the above mentioned
BIO system. Some old models of foggers have an air agitator
or an electric mixing device keeping the mixture moving and
in suspension.
Q 3)
Can we apply water-based chemical mixtures with a
thermal fogger?
Yes, this can be done by:
• Replacing the standard fogging tube by a High Performance
Fogging Tube for water-based fogging mixture. The use of such a
device produces an excellent droplet spectrum. See photo below.
• Use the BIO technology from pulsFOG.
• Add to the water-based pesticide preparations, a antievaporation agent, such as a glycol formulation with a neutral
surfactant such as biodegradable non ionic surfactant.
Biological active substances based on Bacillus thuringiensis var.
israelensis and sphaericus or methoprene combined with the
right ground applicator, mounted on all-terrain vehicles or boats,
are an efficient weapon against mosquito larval stage.
Another benefit of the BIO system is that it can be used to apply
pesticides that are highly flammable. New developments in
the BIO system will allow the pesticide to be injected into the
resonator from the pesticide container.
High Performance Fogging Tube. (Source: Swingtec)
Applying larvacides to a lake. (Source: pulsFOG)
APPLICATION IN CONFINED SPACES:
Using the appliance, an area of approximately 1,000 m2 can be treated from one location. Larger areas are treated in sectors, each being
approximately 1,000 m2.
CALCULATION OF THE OUTPUT RATE FOR SHOULDER CARRIED FOGGING UNITS AND PORTABLE THERMAL
FOGGERS:
This is the same as for the vehicle mounted fog application. Only the walking speed, the swath width as well as the dosage is different.
Example:
Walking speed:
2 km/hr = 2000 m/hr
40 m
Dosage:
2 L/ha (2L /10,000 m )
4,000 m x 40 m x 2L 2 x 4 x 2L
=
2
1.0 ha x 10,000 m ha
2
=
16 L/ha
The quantity of carrier substance must be added to the “quantity” parameter:
Prepare in accordance with the manufacturer’s instructions per hectare (litre) quantity of the chemical.
+ Carrier substance quantity (L/ha) = Total quantity (L/ha)
CALCULATION OF THE WALKING SPEED:
It is the same as for the vehicle mounted fog application. However the output rate in L/hr should be in accordance with the nozzle used.
The formula used, for the vehicle mounted fog application, is the same.
For example:
40 m
Quantity per ha:
2L
Area:
10,000 m
10,000 m2 x 16 L
2
2L x 40 m x hr
=
16,000 m
80 hr
= 2,000/m/h = 2 km/hr
Output rate (L/h), in accordance with the nozzle used 16 L
CONSIDERATION FOR DIFFERING VISCOSITIES (CHECKING THE OUTPUT QUANTITY)
The output quantities of the nozzles are correct when using fluids with the viscosityu of water, or fluids with a viscosity similar to water.
For preparations or mixtures with different viscosity, the flow rate changes (higher viscosities reduce the flow rate, lower viscosities increase
the flow rate).
The correct output quantity for such fogging mixtures can be determinate following the guidelines depending to the type of fogger.
Normally some guidelines on how to use and maintain the fogger are attached to each newly purchased unit and should be read before
using the fogger.
(Source: Text and examples supplied by Swingtec)
Footnote:
u viscosity; resistance of a fluid to flow (See page 5)
For example: a highly viscous product like a heavy engine oil will have a higher resistance to flow than a low viscosity product such as water.
10 MOTORISED BACKPACK
FOGGING (WITH OR WITHOUT
ULV ATTACHMENTS)
Following the WHO specifications; the weight of the equipment,
when both fuel and pesticide tanks are filled to the recommended
level shall be not exceed 25 kg.
The following guidelines/techniques are for the real genuine
backpack ULV applicators. However the technique can also be used
for the normal backpack mist blowers with or without so called ULV
attachments. The guidelines/technique for fogging presented in this
chapter must be adapted from country to country.
Following WHO’s specifications, ULV applicators should emit a
droplet spectrum with a VMD of below 30 µm, with a majority
of droplets in the range of 10 to 20 µm. As was mentioned
previously, a droplet range 8 to 15 µm is suggested as being ideal
for mosquito control measures.
BASIC POINTS:
(For backpack spraying/ fogging units, with or without
special ULV spray head)
• Each spray squad consists of 4 operators and one supervisor.
• Each operator sprays for 15-30 minutes and then is relieved by
the next operator. He must not fog when tired or sick.
• The supervisor must keep each operator in his sight during the
actual fogging in case he/she falls or needs help for any reason.
• Do not directly fog humans, birds, fish or animals that are in
front of spray nozzles, less than 5 meters away.
• Spray at full throttle. Some machines can run for about one
hour on a full tank of petrol.
Some of the applicators having a ULV attachment cannot meet
these specifications and should NOT be used.
Table 6. ULV comparison using Copper Salts (wettable powder formulations)
HUDSON PORTA-PAK
SOLO PORT 423
TANK CAPACITY
0.83 gal. (3.12 litres)
3 gal. (12 litres)
DILUTION RATE
96 oz. to 5.5 gals. (20.82 litres)
4 oz. per gal. (3.785 litres)
CHEMICAL IN TANK
14.4 ozs (0.4 kg per tank)
12.7 ozs (0.36 kg) per tank
FORMULA OUTPUT
0.047 litres (1.6 ozs) per min
0.5 litres (16.9 ozs) per min
66 minutes
24 minutes
WALKING SPEED/MIN
97 feet (29.6 meters)
SWATH LENGTH
33 feet (10 meters)
7.4 acres (2.97 hectare)
1.76 acres (0.71 hectare)
DISCHARGE TIME PER TANK
AREA COVERED PER TANK
ANIMAL SHELTER FOGGING:
Be sure ALL animals are removed from the shelter.
GENERAL INFORMATION TO BE PROVIDED TO THE
INHABITANTS OF AREAS TO BE FOGGED:
Carefully fog outside shelter, particularly close to the ground,
under the shelter and if possible fog surrounding vegetation.
Note: The following information can be used for all the fogging
done by non-vehicle mounted units.
For outdoors shelters, fog all sides of the supporting structure.
• time of the fogging (example 06:30 hrs to 10:00 hrs)
• all doors and windows should be open
• dishes, food, fish tanks, and bird cages should be covered
• stay away from open doors and windows during fogging, or
temporarily leave the house and/or the treated area until the
fogging is completed
• for those not leaving their housing area, they should remain
indoors away from open door and windows. They must not
stand outside their houses when the surrounding vegetation is
also being treated
• children or adults should not follow the fogging squad from
house to house
• remove animals from shelter and, if possible, secure them
outside the housing area which is being treated
• the drying of seeds on the ground and clothes on a line outside
the house must be temporarily suspended and these items
covered or brought inside the house
For indoor shelters, carefully enter and stay in centre of room and
fog towards all walls, taking care to thoroughly cover the lower
portions. Sweeping horizontal spray motions should be used.
If the places are not been properly prepared, attempt to fog only
the areas where the animal is kept.
FOGGING OF THE OPEN FOOTPATH:
This should be done on both sides of the walkway. It should
be done after the fogging of the house and animal shelter has
been completed.
The insecticide is dispersed as the operator moves at a normal
walking speed, roughly 30 meters/minute. When moving from
one place to another place the nozzle should be held slightly
upwards, to avoid the contamination of the ground.
This fog procedure is less difficult than house and animal shelter
fogging and should be done last.
TIMING OF APPLICATION:
Table 7. Fogging is carried out only when the right weather conditions are present and usually only at a prescribed time.
These conditions are summarized hereby following:
MOST FAVOURABLE
CONDITIONS
AVERAGE CONDITIONS
UNFAVOURABLE
CONDITIONS
Time
Early morning (6:30am to 8:00am)
or late evening (after 5:00pm or
6:00pm depending of the season).
Early to mid-morning or late
afternoon, early evening
Mid-morning to mid-afternoon
Wind
Steady, between 3 - 13km/hr
0 - 3 km/hr
Medium to strong over 13 km/hr
Rain
No rain
Light showers
Heavy rain
Temperature
Cool
Mild
Hot
(Source: WHO/WPRO)
For optimum fogging conditions please note:
• In the early morning and late evening hours, the temperature
is usually cooler. Cool weather is more comfortable for workers
wearing protective clothing. Also, adult Aedes and Anopheles
mosquitoes are most active at these hours.
• In the middle of the day, under conditions of higher temperatures
the fog will be carried into higher levels in the atmosphere due to
convection currents, rendering the spray less effective.
• An optimum wind speed of between 3-13km/hr enables the
spray to move slowly and steadily over the ground, allowing for
maximum exposure of mosquitoes to the spray. Air movements
of less than 3km/hr may result in vertical mixing, while winds
greater than 13km /hr disperse the spray too quickly.
• In heavy rain, the spray generated loses its consistency and
effectiveness. When rain is heavy, fogging should stop, and the
spray head of the ULV machine and the thermal fogger should
be turned down to prevent water from entering the blower or
the combustion chamber.
• Fogging is permissible during light showers. Also, mosquito activity
increases when the relative humidity reaches 90%, especially
during light showers.
(Source: WHO/WPRO)
FREQUENCY OF APPLICATION:
The commencement and frequency of fogging generally
recommended is as follows:
• Fogging is started in an area (residential houses, offices,
factories and schools) as soon as possible after a DF/DHF case
or malaria cases, from that area is suspected.
• At least one treatment should be carried out within each
breeding cycle of the mosquito (seven to ten days for Aedes).
Therefore, a repeat fogging is carried out within seven to ten
days after the first fogging. The time the dengue virus incubates
(eight to ten days) in the mosquito is also important, but some
adults will be infected from the egg and be ready to bite and
infect as soon as they mature.
Note that an area much greater than the target should be fogged
to help protect reinvasion from adjacent sections.
SOME SPECIFIC COMMENTS ON FREQUENCY OF
OUTDOOR APPLICATION:
1 New set-up or no previous history of fogging at a site.
•This assumes heavy population of mosquitoes from day 1.
•Start off by fogging each day for the first 2 days.
These two applications at a very short interval will have a
tremendous impact in retarding further population build up due
to the high likelihood of mortality to egg-laying females (gravidu)
throughout this period.
•Subsequent fogging on a seven (7) day cycle.
•After several weeks/months of a weekly fogging regime, it
would be appropriate for the operator to review the situation.
If there is a noticeable drop in the mosquito population, a
fogging of 10-12 days may be used.
It all comes back to observation of the local population dynamics:
if the mosquito population falls off dramatically, there is no need
to keep on fogging, and it may be several months when no
fogging is required.
However, the management system needs to be aware that as
soon as conditions change, and population start to build up, a
fogging program needs to recommence immediately.
2 Epidemic situation (e.g. a site with many malaria or dengue cases).
•Start off with fogging every day for the first 3 to 4 days.
•After the fourth day, revert to a 7 day fogging cycle.
Note: If the epidemic continues after being on a 7 day cycle,
repeat step one before reverting back to weekly fogging’s.
Once the epidemic is under control and the mosquito population
is in decline, a longer cycle can be contemplated. As mentioned in
option (1) above.
These applications should not allow any Anopheles/Aedes in the
area to transmit malaria/dengue.
Note: The frequency of the applications will be the same for
indoor fog application.
EVALUATION OF EPIDEMIC FOGGING:
Within two days after fogging during outbreaks, a parousv rate
of 10% or less, in comparison to a much higher rate before the
treatment, indicates that most of the mosquito population is
newly emerged and incapable of transmitting the disease. This
also indicates that the fogging was effective and greatly reduced
transmission by killing the older infected mosquito population.
A low parous rate after fogging can occur in the absence of a
marked reduction in vector density. This can be attributed to the
emergence of a new population of mosquitoes which escaped
the fog, a relatively low adult density before fogging and adult
sampling methods which show considerable variations in density
in the absence of control.
An effective fog programme also should be accompanied by a
reduction in hospitalized cases after the incubation of the disease
in humans (about 5 to 7 days) have elapsed. The fogging should
be repeated at 7 days intervals to eliminate the possibility of
infected mosquitoes. The time between two treatments can be
changed due to the temperature, and sometimes an interval of 10
days will provide acceptable results
APPLICATION IN CONFINED SPACES:
Using the appliance, an area of approximately 500 m2 can be
treated from one location. Larger areas are treated in sectors, each
being approximately 500 m2.
Footnote:
u Gravid: Female mosquito carrying/developing eggs.
v parous: term describing female mosquitoes that have oviparity (act of laying eggs) at least once.
CALCULATING THE OUTPUT RATE:
The calculation of the flow rate is the same as for the portable thermal fogging unit. However as the walking speed, the swath width and
the dosage are different so that the formula will be:
Example:
Walking speed:
2 km/hr = 2,000 m/hr
2,000 m x 30 m x 1 L
Effective swath width: 30 m
Dosage:
1.0 ha x 10,000 m 2
1 L/ha (1 L/10,000 m )
2
60,000 L
=
10,000 m2
= 6 L/hr
CALCULATING THE WALKING SPEED:
A similar calculation is done as for the thermal fogging unit, taking into consideration the changes of the swath wide, the quantity per ha
and the output rate. As the area is the same no changes are made to the formula.
Example:
30 m
Quantity per ha:
1L
Area:
10,000 m2
10,000 m2 x 6 L 60,000 m
=
= 2000 m/hr=2 km/h or 30 - 35 m/min
1 L x 30 m x hr
30 hr
Output rate (L/hr, in accordance with the nozzle used): 6 L/hr
(Source: Above mentioned calculations courtesy of Swingtec)
CONSIDERATION FOR DIFFERENT VISCOSITIES /
CHECKING THE OUTPUT QUANTITY
Please refer to the portable thermal fogging unit in the
previous pages.
CALIBRATION OF BACKPACK FOGGERS
Space spraying operations with portable backpacked ULV machines
can be accurately adjusted for droplet size and discharge rate. It
is recommended that calibration of machines should be routinely
carried out to ensure best performance of the machine.
1. Detailed Calibration Procedures
•Perform procedure under ideal operating conditions.
•Pour about one litre of oil/petrol fuel mixed into fuel tank
(the mixture is dependant of the type of machine used. Read
the instructions).
•Pour one litre of test solution (recommended insecticide
formulation used for the vector control program) into the tank.
•Start the unit (according to manufacturer’s instructions) and
allow running for three minutes.
•Direct discharge horizontal.
•Open solution tap and allow discharging for 10 minutes
(record the discharge time).
•Close solution tap and note elapsed time.
•Shut off engine and close petrol tap.
•Disconnect discharge tube and allow insecticide tank contents
to drain into a graduated cylinder.
2. Working Example
•Original contents:
1,000 mL
•Balance:
720 mL
•Amount discharged (10 minutes): 280 mL
•Discharge per minute:
28 mL
Repeat discharge operation two or three times and average
the results.
(Source: WHO/WPRO)
11FOGGING WITH HAND
HELD EQUIPMENT
This method called RISSA (Residual Indoor Space Spraying
Application) has proven to be more efficient, economical and
effective than traditional thermal fogging procedures.
While it is well known that thermal fogging and ULV sprays are
not residual applications, researchers have developed a system in
which a scientifically engineered formulation provides a residual
wall spray as well as an airborne contact kills via ULV particles for
indoor applications.
In the beginning, alpha-cypermethrin was used, but this insecticide
was very irritating to the applicant’s skin, eye and nose. However it
was a high performance insecticide and a single residual application
lasted a long time, does not build up in the environment and is
extremely effective. The droplets contain crystalline particles that
adhere to all types of surfaces. It has bi-modal action: it works as a
contact kill via airborne aerosol particles expelled by the hand held
sprayer, and through ingestion and absorption by the mosquitoes
that are resting on different surfaces.
FOGGING TECHNIQUE:
Contrary to the other spraying operations, the entire house will
not be treated. Only the places where the mosquitoes are hiding
will be treated (dark areas, underneath heavy furniture, which
can be hardly moved, cupboards, beds etc…) as well as the
walls and resting surfaces. Despite that all precautions taken, to
spray only the already mentioned surfaces, there will be some
spray droplets flying and falling on other places. This is a normal
fact and will not interfere with the expected results.
The fogging of one room should take approximately 15 seconds.
Typical thermal fogging applications, in a dengue emergency,
occur every three days. In the beginning when the tests with
RISSA were done, satisfactory results were seen for a period of up
to 21 days. Now the residual effect must be longer so that such
type of application is greatly reducing the cost of labour, fuel and
chemicals as well as the inconvenience to the homeowner for
evacuating their house.
Using the right insecticide, knockdown and mortality occurs within
30 minutes. In the RISSA application, the mosquito is exposed to
several particles while in flight and while harbouring in suitable
resting spots within the house.
12 ANNEXES
ANNEXE 1
PREPARATION OF SPRAY SOLUTION TO KILL ADULT MOSQUITOES DURING DHF OUTBREAKS.
The general formula is the same as for preparing solutions to treat mosquito nets.
X = (A/B) - 1
Where:
X = parts of water/solution to be added to 1 (one) part of the insecticide.
A = concentration of the insecticide (%)
B = required concentration of the final solution (%)
a)Example:
Assume a 1 % solution of permethrin (or other suitable pyrethroid) is to be prepared from a 25% concentrate and used in a back-pack
sprayer with or without ULV attachments.
X = (25/L) -1 = 24
Therefore 24 parts of water to 1 (one) part of concentrate are required.
If the fogger has a capacity of 6 litres, there is a need of 250 mL (6 L = 6,000 mL: 24 = 250 mL) of concentrate to six litres of water or
kerosene, e.g. 5750 mL of water or kerosene and 250 mL concentrate.
b)Example
A 1 % solution of permethrin or other suitable pyrethroid is to be prepared from a 10% concentrate and used in a back-pack sprayer
with ULV attachments.
X = (10/1) – 1 = 9
Therefore nine parts of water or kerosene to 1 (one) part of concentrate are required or 667 mL of concentrate to 6 litres of water or
kerosene, or 600 mL to 5.4 litres of water or kerosene, better 5333 mL of water or kerosene and 667 mL of concentrate.
c)Example
A 4% solution of malathion or pirimiphos-methyl is to be prepared from a 50% concentrate and used in a hand-carried thermal fogger.
X = (50/4) - 1
12.5 - 1 = 11.5
Therefore 11.5 parts of diesel oil to 1 (one) part of concentrate are required or 100 mL of concentrate to 1,150 mL of diesel oil.
d)Example
A 4% solution to be prepared from a ULV concentrate (98% technical) and used in a vehicle-mounted thermal fogger.
X = (98/4) - 1
25.5 - 1 = 23.5
Therefore 23.5 parts of diesel oil to 1 (one) part of concentrate are required or 425 mL of concentrate to 10 litres of diesel oil.
A ULV concentrate (95% technical) of Malathion (also know as Maldison in some countries) is to be used in a vehicle mounted ULV fogger.
No dilution is necessary.
(Source: WHO/WPRO)
ANNEX 2
SAFETY PRECAUTIONS:
Please read and understand all product labels and relevant
Material Safety Data Sheets (MSDS) before starting a fogging
program. If unsure of any details, please seek advice from the
project supervisor.
Note: Safety measures in insecticide use are adopted to
protect the health and lives of those applying insecticides.
These measures seek to minimize the degree of poisoning by
insecticides and the exposure to insecticides, prevent accidental
poisoning, monitor sub-acute poisoning and provide adequate
treatment for acute poisoning. These measures can be broken
into four broad categories:
• the choice of insecticides to be used
• the safe use of the insecticides
• the monitoring of insecticide poisoning
• the treatment of insecticide poisoning
What to know and what to do.
1 It is important to recognise of the symptoms associated with
toxic levels of the individual pesticides used and what can be
done to prevent exposure to these products. This concerns
the indoor as well as outdoor fogging, and the use of all kind
of units. The safety precautions for the ULV and/or thermal
fogging must receive full attention. One operator, due to
rotation, will not fog more than 40 to 60 minutes in one day
but he will be in the spray area for several hours and thus be
exposed to drifting droplets.
2 Certain basic rules must be observed:
•treat all insecticides with care and attention and always follow
the safety directions on the label on the insecticide packing.
Always wear protective clothing, and ensure that the legs
of the overalls are not tucked inside the gumboots. They
must stay outside the gumboots. The same applies with the
sleeves outside the gloves. Take particular care when using
organophosphate products in fogging operations.
•any spillage of the liquid concentrate onto the skin must be
immediately washed off using soap and water.
•all operators must always wear gauze masks and goggles.
The goggles also protect against flying dust and other
particles whilst fogging animal shelters.
•the motor of the fogger must be switched off before petrol or
insecticide are re-filled.
•an operator who becomes accidentally contaminated with the
liquid insecticide due to sudden leakage or breakage in a line
or otherwise, must immediately change his uniform and wash
with soap and water the contaminated area of his body.
•a clogged nozzle tip will cause insecticide to drip into the large
blower tube and this insecticide cannot be expelled forward,
but will back up in the tube and drip through a small “safety”
opening, When the latter occurs, the lower portion of the
sprayer’s back will become contaminated. This important rear
area of the sprayer should be periodically inspected and steps
taken to ensure that the nozzle tip does not become clogged.
3 Symptoms of Poisoning
The blood cholinesterase determinations for organophosphates
or carbamates, after the first two rounds of fogging, and each of
the next three rounds, will give an indication if any operator has
had too much exposure to the insecticide, even though he may
not show any toxic symptoms.
However, it is good to know early symptoms of poisoning
which include the following:
•excessive sweating,
•headache
•blurred vision
•dizziness
•sick feeling (nausea)
•vomiting
•stomach pains
•slurred speech
•muscle twitching (convulsions may occur in later symptoms).
4 The supervisors should be informed and alerted regarding
any possible poisoning so that first aid measures can be
implemented. The drug (Atropine) used to stop some of the
poisoning effects must be available and present in the area
where fogging operation are taken place. The sick person and
these drugs can be directly transported to the local health
facilities, who already know how to treat poisoning cases. Bring
also the insecticide label/packing to the health centre so that
the medical staff can see what antidote must be given.
OTHER ADDITIONAL SAFETY INSTRUCTIONS AND
ACCIDENT PREVENTION:
• Read and understand the operating manual for each type of
equipment first.
• Never add fuel when the unit is hot (Fire hazard)
• Never add fuel into the solution tank (Fire hazard)
• Never touch the fogging pipe tip while the engine is running.
Do not touch the protection jacket (cooling jacket) for 30
minutes after stopping the engine (danger of injury due to
radiated heat).
• Never let the unit run without supervision.
• Do not transport hot units in closed vehicles. Never ship the
unit with fuel or insecticide in the tank. If there is still fuel in
the tank, the unit must be upright and secured against spillage.
Remove the spark plug cap from the spark plug. Only remove
or connect the spark plug cap from/to the spark plug with the
fuel tank closed (because of the risk of formation of sparks).
• When filling one of the tanks or when inspecting the carburettor,
smoking is strictly prohibited in the immediate environment.
• Do not fog any liquids with a flash point of less than 75°C.
• After any repair work, reinstall the protection features on the unit.
• Eliminate any leakage occurring on the unit without delay.
• Check the functional safety of the unit each time before using it.
For stationary operation, ensure safe standing for the unit.
• Units which are permanently in use must be checked for
compliance with the safety and accident prevention regulations
whenever servicing or repair work is carried out in the
customer service workshop or in the manufacturer’s servicing
department.
• Observe the instructions for use supplied by the pesticide
manufacturers.
• When fogging, use protective equipment such as protective
clothing, gauze mask, protective gloves and ear protectors as
applicable. The type and quality of the protective equipment
to be used depends on the agent manufacturer’s instructions.
The filter for the gauze mask (full-face musk) must meet the
protection category A2B2-P3 as a minimum requirement.
• Always wear ear protection equipment.
ANNEX 3
DETERMINING DROPLET SIZES
Directions for determining the droplet size of Malathion - non thermal aerosols.
Note: For this example, droplet determination for Maldison has been used. For other insecticides ,the methodology is the same,
however check with the manufacturer for appropriate coated slides and spread factor.
• Droplets that are too large (100 - 500 µm) will not carry well through the air and will not effectively reach the target insects. Also with
droplets in this size range even when impingement occurs there is an overkill and waste of insecticide.
• Droplets too small (less than a single µm) will flow over the target rather than impinge upon the body of the insect.
• Correctly sized droplets make the necessary contact with target insects and effectively do the job of killing the target organism.
Source: Micron Generation: Optimum Pest Control Through Optimum Sized Insecticide Droplets. Micro-Gen Equipment Corp. 1977
DETERMINATION OF DROPLET SIZE:
Note:
• The following information is based on the directions for determining the droplet size of Malathion non-thermal aerosols and the use of
silicon-coated slides.
• That the test method used for Maldison is applicable for other insecticides; however manufacturer recommendations must be adhered to.
Important work in this area was done in the past by Dr. G.A. Mount.
We can’t neglect that the droplet size plays a very important role in pesticide application by minimizing environmental contamination.
Pesticides sprays are generally classified according the droplet size. When drift is to be minimized a medium coarse spray is required
irrespective of the volume applied. (See Table 8). Droplet size is one of the principal factors affecting the efficiency of insecticide sprays or
aerosols for the control of adult mosquitoes.
CLASSIFICATION OF SPRAYS ACCORDING TO DROPLET SIZE.
Table 8. Droplet size spectrum
VOLUME MEDIUM DIAMETER OF DROPLET (µm)
CLASSIFICATION OF DROPLET SIZE
< 0.001 µm
Vapours
0.001 - 0.1 µm
Smoke and Fumes
0.1 - 50 µm
Aerosols and Fogs
51 - 100 µm
Mist
101 - 200 µm
Fine spray
201 - 400 µm
Medium spray
> 400 µm
Coarse spray
Droplet size should be determined as frequently as necessary to insure that proper droplet size is maintained for each operation. It is
suggested that droplet size determination be made:
• every time the spray generator is installed on a vehicle
• after each two months, thereafter every 50 hours (whichever is sooner) of operation
• after any accident
• random checking
• if the spray generator remains idle for a month of more recalibration and droplet size evaluation are advisable.
• following manufacturer’s instructions, on cleaning and maintenance must be followed to obtain proper droplet size.
OPTIMUM DROPLET SIZE RANGE:
As a general recommendation the droplet size for ground fogging
operations, should be in the range of 10 to 15 µm VMD. Within
this general recommendation, there are a number of specific
issues that need to be taken into consideration:
1.The VMD of the droplets SHOULD NOT exceed 17 µm.
2.Individual spray droplets SHOULD NOT exceed 32 µm in
size. Three (3%) percent of the spray droplets (6 droplets in
200 droplets) can exceed 32 µm providing the VMD does
not exceed 17 µm and no droplets exceeds a maximum of 48
µm. Larger droplets when transported by natural air currents,
impinge more readily on objects in their pathway and will
permanently damage automobile-type paints.
3.More than one half of the total spray mass must consist of
droplets in the 6 to 8 µm range in order to achieve adequate
dispersal over a 100 m (300 feet) swarth.
4.A minimum of 66% (preferrably 80%) of the total spray mass
must consist of droplets NOT EXCEEDING 24 µm in size.
(Source: Cyanamid Publication 1987)
EQUIPMENT REQUIRED
• Microscopes capable of 400 x power
• Stage micrometer (200 divisions x 0.01 mm or 10 µm = 2 mm)
• Eyepiece micrometers suitable for the available microscope
•Counter
• Slide: Different kinds of coated slides are available on the
market. They have the same measurements as the normal
microscopic slides 2.5 x 7.5 cm (1 inch x 3 inch).
Silicon coated and magnesium oxide coated slides are accepted
as being the method of choice for water-based formulations
(Rathburn. 1970). Teflon coated microscope slides are
recommended for collecting droplets where oil is used as a
diluent, such as malathion and pyrethroid insecticides. Silicone
coatings are miscible with oil formulations and will produce
erroneous results.
Teflon coated is recommended for collecting droplets where oil is
used as a diluent such as fyfanon and pyrethroid insecticides.
Teflon coated slides, are suitable for all sample
applications, if silicon or magnesium coated slides are
not available.
CLEANING
To clean a used Teflon coated slide we recommend using cotton
moistened with acetone, xylene, alcohol or similar solvent. Do NOT
use cloth or lens paper as this will scratch the surface of the slide.
FACTORS WHICH AFFECT SPRAYS APPLIED FOR
MOSQUITO CONTROL;
A.Meteorological
•Wind: intensity, directions turbulence
•Temperature
B.Humidity
•Sunshine: promotes turbulence and thermal ascending
currents, degrades photosensitive pesticides
C.Formulation
•Viscosity
•Vapour pressure
•Specific gravity
•Spreading characteristics
D.Toxicity
•Toxicity to insects
•Toxicity to man and warm blooded animals
•Toxicity to plants
E.Equipment factors or related characteristics
•Droplet size
•Nozzles employed
•Air currents at time of fogging
•Nozzle types, sizes position
F. Liquid pressure
INSTRUCTIONS
PROCEDURE FOR DROPLET COLLECTION:
To make a magnesium oxide; coated one, burn magnesium
ribbon a few centimeters below the glass slide; two strips of
magnesium ribbon, each about 10 cm long, will produce a deposit
sufficiently thick for droplet diameters of up to 200 µm to be
measured. A simply method of checking the uniformity of the
coating is to view the coated slide from the back and against the
light. The lower limit of droplet size that can be detected with a
magnesium-oxide-coated slide is about 10 µm.
There are several techniques which can be used.
A.Laser-based techniques.
•They are expensive and essentially laboratory-based instruments.
B.Hot wire anemometry.
•This is an electronic method that is both fast and convenient.
The technique can be used to check the droplet spectrum
produced by cold foggers, but is not suitable for use of
thermal foggers.
C.Slide wave technique.
• If modern equipment is not available, simple assessments can
be made using the slide wave technique, using coated glass
microscope slides. The technique can be done as follow:
1) Collect droplets under ideal operating conditions e.g.
•no rain
•no strong wind e.g. wind speed below 15 km (10 miles)
per hour.
2) Start the spray generator and allow discharging for a
couple of minutes. Once the motor is working, the flow
rate can be eventually checked.
3) Contradictory to other treatment operations, the nozzle
is more conveniently positioned parallel to the ground to
discharge horizontally.
4) Stand behind the generator and move one step side warts
and go than three to 4 meters away from the generator.
5) Once the sampler stands 3-4 meters behind the nozzle,
just out of the spreading cloud of droplets, he/she swings
the slide into the cloud and toward the nozzle against the
direction of travel of the particles, horizontally and very
quickly. The object is to swing the slide into the moving
cloud and to get the most speed possible between the
particles accelerated out of the nozzle and the slide being
swung by the sampler. The higher the speed, between
the particles and the slide, the better the sample because
the smaller particles only hit and stick on the slide at
higher speed. In sportive terms we can say “a baseball
swing with the nozzle as pitcher”.
6) A sample of the aerosol is deposited on the slide by
waving the side through the aerosol cloud. The slide
velocity may be increased by attaching it to a 1.5 to 2.0
m (3 to 4 foot) stick by means of a spring paper clip or
a rubber band. A single passage is generally sufficient
to collect a representative sample. Stay 3 meters from
the nozzle tip. It is advisable to take 2 slides; although in
most of the programs only one single slide is taken.
7) If the slides aren’t examined locally, place the slides in
a tight box and return them to the laboratory or office,
where it must be stored in a cool place (refrigerator if
possible) waiting to be examined. Avoid excessive heat
during the transport, and prevent them from evaporation.
FACTORS TO CONSIDER IN SELECTION OF DROPLET
SIZE (USING MALATHION AS AN EXAMPLE).
A.If droplet size is too large:
•There will be fallout before the swath width of 100 m (300 feet)
is reached.
•Coverage is much reduced since fewer droplets are produced
with the same amount of insecticide.
•Droplets sizes larger than 17 µm, VMD may spot car paint,
while those bigger than 25 µm, adhere more readily than small
droplets and may be filtered out by vegetation and other objects.
•With those larger droplets there will be a waste of insecticide
and as more insecticide is used, there will be an increase in
pollution and toxicity to non target organisms.
B.If droplet size is too small:
•All he droplets are subject to upward convection currents of
turbulent air and they may not impinge on adult mosquitoes,
although a flying mosquito will pick up more droplets than a
resting one.
•If the droplet size is less than 8 µm, a single droplet may
not kill a mosquito.
SLIDE EXAMINATION:
• At least 200 droplets should be measured. This can be done
on one slide. All the droplets from the edge of the slide to the
other are counted as the slide moved across the field by the
mechanical stage. Measurements should NOT be taken along
the margins of the slide.
• DO NOT put a cover glass on the slide, as it will distort the
droplets. Focus at 100 x (times) or 200 x and then switch over
to read the slide using 400 x power.
• Reduce the brightness of the light below the slide if the light is
variable, or put the piece of cloth between the slides containing
the droplets and the light.
• The droplets will form a dome shape on the slide and the
spread factor is to correct for the spread of the droplet diameter
due to the fact the droplet is of full size, but not a true sphere.
• The height and the diameter of the droplet is used to calculate
the spread factor.
• Droplets are most conveniently measured in terms of the
divisions of the eyepiece micrometer and afterwards converting
the divisions into microns. In the example presented in Table
9 droplets were measured at 400 x magnification. At that
magnification, each division of the eyepiece was calibrated to
equal 3.5 µm.
• The measurements converted into microns must then be
corrected for the amount of spread factor that occurred on
the slides. Do not use uncoated slides as there will be no
spread factor obtainable for them. The use of a spread factor
in the calculations is absolutely necessary and is very different
for each pesticide and formulation of that pesticide. The
determination of a spread factor is very exacting and must
be done with great care by a trained microscope operator. It
should be available from the manufacturer of the pesticide
but usually is not easy to obtain as it is not used often. The
marathon ULV concentrate spread factor for silicone-coated
slides is 0.5 (In Teflon coated slides the spread factor is 0.69).
Therefore, in Table 9, each division of the eyepiece is 3.5
µm times the spread factor 0.5 µm or 1.75 µm which is the
conversion factor.
The measurements are arranged in order and processed as in Table
9. The maximum diameter is calculated by converting the diameter
of the largest droplet measured into microns. In Table 9, the
largest droplet measured had a diameter of 19 eyepiece divisions.
Therefore the maximum diameter is 33.3 µm (19 x 1.75 = 33.3).
To determine the Mass Medium Diameter (MMD), the accumulative
percentages from the last column in Table 9 are plotted against the
eyepiece divisions (D) on arithmetic probability paper as in Graph 1.
Directly across from the 50 percent point on the line is the medium
droplet size in eyepiece divisions which must be converted to
microns. In Graph 1 eyepiece divisions times the conversion factor
of 1.75 equals a Mass Medium Diameter (MMD) of 16.1 µm.
Table 9. Calculated Data: Malathion Concentrate Aerosol Droplets Impinged on Microscope Slides
EYEPIECE DIVISIONS
(D)*
NUMBER OF
DROPLETS COUNTED
(N)
DXN
% OF TOTAL
DXN
∑(D X N)
ACCUMULATIVE
%
1
5
5
0.31
0.31
2
10
20
1.22
1.53
3
9
27
1.65
3.18
4
12
48
2.93
6.11
5
15
75
4.58
10.69
6
12
72
4.40
15.09
7
25
175
10.70
25.79
8
14
112
6.85
32.64
9
28
252
15.40
48.04
10
19
190
11.61
59.65
11
14
154
9.41
65.06
12
10
120
7.33
76.39
13
6
78
4.77
81.16
14
4
56
3.42
84.58
15
11
165
10.09
94.67
16
2
32
1.96
96.63
18
2
36
2.20
98.83
19
1
19
1.16
99.99
Total
199
1636 = ∑(D x N)
* Measurements were taken at 400x magnification. Each eyepiece division equals 1.75 µm (3.5 µm x the 0.5 spread factor).
DIRECTION ON HOW TO MEASURE THE DROPLET
SIZE PROVIDED BY THERMAL AEROSOLS:
Thermal fog particle testing can be done adequately with the
Maldison method if the spread factor is known for the formulation
and the test is done before the solvent evaporates (Aqua
Formulations and kerosene). Do not use uncoated slides as there
will be no spread factor obtained for them.
Thermal fog particle size is usually determined visually and it
is suggested as a medium fog, not too wet and heavy or too
dry and light. Note the action, does it hang or does go up and
down. Thermal fog will always go up, but at the speed at which it
goes up should be minimized. A relatively dense, relatively still a
relativity vertically stable fog is what is desired.
All the needed parameters as for ULV spraying, inversion, target
insect presence, wind and speed below 10 mph (15 km) and not
raining, are still required. Be informed that standard thermal fog
generators, no matter which model is used, the droplet spectrum
is reaching from very small droplets up to large droplets of 200
µm or more, depending to the nozzle used.
Graph 1. Determination of the Mass Median Diameter (MMD). Redrawn from Malathion Insecticide for Adult Mosquito
Control, Cyanamid
18
0.01
0.1
1
2
5
10
20
30 40 50 60 70 80
90
95
98 99
99.99
0.01
0.1
1
2
5
10 20 30 40 50 60 70 80
Accumulative Percentage
90
95
98 99
99.99
17
16
Corrected Eyepiece Divisions (1 Division = 1.75 microns)
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Percentage of the total volume of aerosol samples below each droplet size( from table 9). The MMD is determined from the 50% point on the line. The MMD
equals 9.2 divisions x 1.75 equals 16.1 µm
13 SELECTED REFERENCES
Annex X: Guidelines for Chemical Space Spraying (SEARO).
WHO Publication from SEARO (South East Asian Regional Office)
Communicable Diseases Control, Prevention and Eradication WHO Pesticide Evaluation Schema (WHOPES)
WHO publication (2003)
Directions for determining the droplet size of Cythion or Malathion ULV nonthermal aerosols (Cyanamid 1987)
Effective Disinfection with Thermal Fogging. DRAMM Publication (2011)
Guidelines for Assessing the Efficacy of Insecticidal Space Spraying for Control of the Dengue Vector Aedes aegypti (World Health
Organization 2001).
Guidelines for Dengue Surveillance and Mosquito Control Second Edition (World Health Organization 2003). Manila. Second Edition 2003.
Leading water-based space-spray technology for the control of mosquitoes and flies, 0410 Edition ©2010 Bayer Environmental Science
Micron Generation: Optimum Pest Control Through Optimum Sized Insecticide Droplets. Micro-Gen Equipment Corp. 1977
Operating instructions portable thermal sprayer manual (pulsFOG).
Regional Guidelines on Dengue/DHF, Prevention and Control (Regional Publication 29/1999).
WHO publication
Space spraying application of insecticides for vector control and public health pest control. A practitioner’s guide. Communicable Diseases
Control Prevention and Eradication.
WHO Pesticide Evaluation Scheme (WHOPES)
The use of fog generators in Integrated vector Control: Thermal fog and cold fog (ULV) generators. (Swingtec).
14 ABBREVIATION REFERENCE
Bti =
Bacillus thuringiensis var. israelensis – product
C
=
Celsius (eg: 75°C)
DF/DHF
=
Dengue Fever / Dengue Hemeragic Fever
ha =Hectare
hr =Hour
hrs =Hours
kcal =Kilocalories
km =Kilometres
kph
=
Kilometres per hour
km/h
=
Kilometres per hour
kW =kilowatt
L =Litre
LV
=
m =Metre
m/s
mL =Millilitre
=
Low volume
Metre per second
MMD
=
Mass Medium Diameter
mph
=
Miles per hour
RISSA
=
Residual Indoor Space Spraying Application
ULV
=
Ultra Low Volume
VMD
=
Volume Median Diameter
WHO
=
World Health Organisation
WP
=
Wettable Powder
WPRO
=
Western Pacific Regional Office (Manilla)
x =Times
÷ =Division
µm
=
Micron (0.001 millimetre)
NOTES:
1.The insecticide Malathion is known as Maldison in a number of different countries. Either name is applicable when referring to this
insecticide.
2.MMD and VMD are synonymous and interchangeable. MMD is considered to be an older term and most recent technical literature tends to
use the term VMD.
3.Before using any type of equipment, read the operator’s manual.
4.Prior to using any pesticide in a fogging program, read and heed the label.
15 ACKNOWLEDGEMENTS
Mr. Mario Valvasori (Southern Exports (Australia) Pty Ltd). Mr Terry Armstrong (Newtonian Consultancies) and Mr. Kern Walcher (Practical
Vector Control (USA)), for revising the technical content of this manual.
The assistance provided by Mr Bernd L Dietrich (Executive Shareholder of MOTAN Swingtec GmbH) and Mr Werner Stahl (pulsFOG, Dr
Stahl & Sohn GmbH) is gratefully acknowledged. Both gentlemen provided valuable advice on many aspects of the technical details in this
manual, as well as generously allowing the author access to their respective company information manuals and photographs/drawings.
Ms Christelle Lepers, Mrs Elise Kamisan-Benyon, Ms Beryl Fulilagi and Mr Boris Colas, from the Secretariat of the Pacific Community (SPC/
CPS) for providing invaluable assistance to the author.
Mrs Christine Jackman, for assisting in the editing of the final manuscript.
Mrs Elena Collins with formatting the manuscript prior to printing.
ABOUT THE AUTHOR
Lucien Swillen is a former World Health Organisation Technical Officer who has worked in many parts of the world. His 30 year career with
WHO (1963 to 1993) was principally involved with the control of Malaria and Dengue Fever, as well as in programs to control such diseases
as Trypanosomiasis and Schistosomiasis.
His career at WHO took him to such diverse countries as:
• The former Yugoslavia, Turkey and Algeria;
• The former Republic of South Vietnam, New Hebrides (now Republic of Vanuatu), Solomon Islands and Laos.
• Upper Volta (now Burkina Faso), the Republic of Mali and the Ivory Coast.
Following his retirement from WHO, Mr. Swillen has based himself in the South Pacific region and has continued his interest in Malaria and
Dengue Fever control, by continuing to work in these fields. He spent more than 10 years representing several international manufacturers
of mosquito vector control equipment and other companies working in commercial vector control programs.
Since 2006, Mr. Swillen has worked as a freelance consultant. He has helped organize and conduct workshops/courses for the WHO,
Secretariat of the Pacific Community (SPC) and HD Hudson in most of the countries of the Pacific Region as well as in Saudi Arabia,
Nigeria, Iran, Timor Leste and the Philippines. In this time, he has been involved in numerous workshops where his particular expertise as a
field operator has seen Mr. Swillen conducting “train the trainer” exercises in the correct techniques for Residual Indoor Spraying Programs
and Space Spraying programs as well as passing on his wide-ranging expertise to a new generation of field officers involved with public
health programs.
Mr. Swillen currently resides in New Caledonia and continues his involvement in the control of Malaria and Dengue Fever; he is currently
researching the early history of Malaria control in the Republic of Vanuatu since the islands were first discovered by European missionaries
up until the country’s independence in 1980.
The author may be contacted via: sinekci@lagoon.nc
December 2013
NOTES
NOTES
NOTES

The Use of Fog Generators in Integrated Vector

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