Whereas conventional insecticides work by the pest species making contact with the dried toxic deposits or of airborne or surface dry particles or liquid droplets, often by way of the cuticle but sometimes by ingestion, fumigants always work in the gaseous form, entering the pest’s body through it’s respiration system - the spiracles in the case of the invertebrates.

1. Digital Re-print -
March | April 2014
What is Fumigation?
- A technique of pest control using a toxic gas
www.gfmt.co.uk
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2. W
hereas conventional insecti-
cides work by the pest species
making contact with the dried
toxic deposits or of airborne or surface dry
particles or liquid droplets, often by way
of the cuticle but sometimes by ingestion,
fumigants always work in the gaseous
form, entering the pest’s body through
it’s respiration system - the spiracles
in the case of the invertebrates.
True fumigants should be differentiated
from insecticidal smokes, fogs and mists,
which are often incorrectly referred to as
fumigants. Fumigants are gases, which dif-
fuse as separate molecules, penetrating into
the materials being fumigated. The com-
pletion of a fumigation requires aeration
or ventilation which removes all traces of
the fumigant gases, although other residues
may remain, which will be discussed later.
Smokes, fogs and mists are air-borne sus-
pensions of solid or liquid particles, which
will be deposited on the outer surfaces of
the materials being treated (foods, packag-
ing or structure) without any degree of
penetration. For example, it is quite com-
mon to hear farm workers talking of fumi-
gating their grain stores, as they prepare to
apply a canister of a pesticidal smoke. The
smoke generator can seem very impressive,
but will have almost zero penetration into
sacks and bags or into dried food spillage.
It is only true fumigants that can kill pests
hiding in deep deposits of spillage or of
the foodstuffs themselves. We will see this
aspect of fumigation again when we discuss
treating grain heaps, or silos and bins of
grain, or flour or bag stacks in food stores.
Fumigant gases kill target pests via the
respiration system, usually by preventing the
transfer of oxygen into the tissues.
Ideally a fumigant will work rapidly, and
not leave an harmful residues. But there
can be other issues with fumigation. Of
the fumigants left in use in the 21st century,
some require quite a high working tempera-
ture (around > 25°C) to effectively control
insect eggs, some need extended exposure
periods (often in excess of 2 weeks con-
tinuous exposure – grain weevils, and spider
beetles, for example, or for the tiny booklice
and mites, sometimes even needing two
fumigations separated by 10 days!
But by far the biggest disadvantage of
fumigation is lack of long-term effect. Once
it’s gone it’s gone! And, unlike the dried
powder or spray deposits of conventional
insect control, fumigated goods are open to
re-infestation immediately after the gas has dis-
persed. It is definitely difficult to use fumigation
as a protective (prophylactic) measure, despite
the claims of some fumigation companies over
the years. All depends on totally protecting the
commodity from further attack.
In fact the real and unique advantage of
fumigation is its penetration through bulks
and all woven bags of dried commodity
Fumigation - its practice and
effectiveness
Because all fumigants are at least as
toxic to all animals, including humans, as
to invertebrates, in Europe and the USA,
fumigation of commodities and buildings
can only be carried out by trained and
certificated fumigation operators. However,
it is very useful for all involved in the storage
of food commodities and working in food
manufacturing plants, to understand the prin-
ciples and practical aspects, and constraints,
What is Fumigation?
A technique of pest control using a toxic gas
by Mike Kelly, Acheta
What is Fumigation?
1. A technique of pest control using a toxic gas.
Whereas conventional insecticides work by the pest species making contact with the dried toxic deposits or of airborne or surface
dry particles or liquid droplets, often by way of the cuticle but sometimes by ingestion, fumigants always work in the gaseous form,
entering the pest’s body through it’s respiration system - the spiracles in the case of the invertebrates.
True fumigants should be differentiated from insecticidal smokes, fogs and mists, which are often incorrectly referred to as
fumigants. Fumigants are gases, which diffuse as separate molecules, penetrating into the materials being fumigated. The
completion of a fumigation requires aeration or ventilation which removes all traces of the fumigant gases, although other residues
may remain, which will be discussed later. Smokes, fogs and mists are air-borne suspensions of solid or liquid particles, which will
be deposited on the outer surfaces of the materials being treated (foods, packaging or structure) without any degree of
penetration. For example, it is quite common to hear farm workers talking of fumigating their grain stores, as they prepare to apply
a canister of a pesticidal smoke. As seen below, the smoke generator can seem very impressive, but will have almost zero
penetration into sacks and bags or into dried food spillage. So it is only true fumigants that can kill pests hiding in deep deposits of
spillage or of the foodstuffs themselves. We will see this aspect of fumigation again when we discuss treating grain heaps, or silos
and bins of grain, or flour or bag stacks in food stores.
Fumigant gases kill target pests via the respiration system, usually by preventing the transfer of oxygen into the tissues.
Ideally a fumigant will work rapidly, and not leave an harmful residues. But there can be other issues with fumigation. Of the
fumigants left in use in the 21
st
century, some require quite a high working temperature (around > 25°C) to effectively control insect
eggs, some need extended exposure periods (often in excess of 2 weeks continuous exposure – grain weevils, and spider
beetles, for example, or for the tiny booklice and mites, sometimes even needing two fumigations separated by 10 days!
But by far the biggest disadvantage of fumigation it is lack of long-term effect. Once it’s gone it’s gone! And, unlike the dried
powder or spray deposits of conventional insect control, fumigated goods are open to re-infestation immediately after the gas has
dispersed. It is definitely difficult to use fumigation as a protective (prophylactic) measure, despite the claims of some fumigation
companies over the years. All depends on totally protecting the commodity from further attack (see later in article)
In fact the real and unique advantage of fumigation is its penetration through bulks and all woven bags of dried commodity
2. Fumigation - its practice and effectiveness
Because all fumigants are at least as toxic to all animals, including humans,
as to invertebrates, in Europe, fumigation of commodities and buildings can
only be carried out by trained and certificated fumigation operators.
However, it is very useful for all involved in the storage of food commodities
and working in food manufacturing plants, to understand the principles and
practical aspects, and constraints, of fumigation, so that they can consider or
recommend fumigation only when it is likely to be the best option.
At the time of writing, 2014, the Montreal Protocol has resulted in methyl
bromide – previously the most frequently-used fumigant - being totally
phased out from European and other developed countries’ fumigations.
Sulfuryl fluoride (SF), previously confined to termite and other wood-boring
insect control mostly in America, has now received limited approval for use on
many timber products including logs, and for use in empty grain storage
situations and emptied flour & feed mills. In the USA SF has a few dried
foods clearances (tree nuts, for example) but not in Europe. The principle
reason seems to be that there will always be a fluoride residue, and in many
situations there is no accepted, listed approval for fluoride in foods, which
helps explain why SF is generally unacceptable for food container imports.
Phosphine (PH3) is the commonest fumigant in use worldwide. It has been
available commercially since the 1950s, originally being produced solely in
Germany, but in recent years also manufactured in India, some South
American countries and China, in formulations very similar to those well
known from Germany.
Hot-Fogging tobacco
warehouse
A Detia Phosphine
dispenser electrically-
powered for silos. This uses
spherical tablets which roll
down a plastic tube and
into the silo, and will result
in a powder contamination
of the fumigated grain
30 | March - April 2014 GRAIN&FEED MILLING TECHNOLOGYF

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4. of fumigation, so that they can consider or
recommend fumigation only when it is likely
to be the best option.
At the time of writing, 2014, the Montreal
Protocol has resulted in methyl bromide –
previously the most frequently-used fumigant
- being totally phased out from European
and other developed countries’ fumigations.
Sulfuryl fluoride (SF), previously confined
to termite and other wood-boring insect
control mostly in America, has now received
limited approval for use on many timber
products including logs, and for use in empty
grain storage situations and emptied flour &
feed mills. In the USA SF has a few dried
foods clearances (tree nuts, for example) but
not in Europe. The principle reason seems
to be that there will always be a fluoride
residue, and in many situations there is no
accepted, listed approval for fluoride in
foods, which helps explain why SF is gener-
ally unacceptable for food container imports.
Phosphine (PH3) is the commonest fumi-
gant in use worldwide. It has been avail-
able commercially since the 1950s, originally
being produced solely in Germany, but in
recent years also manufactured in India,
some South American countries and China,
in formulations very similar to those well
known from Germany.
Phosphine gas is invariably generated on-
site by the action of atmospheric moisture,
or commodity humidity, on solid aluminium,
or magnesium, phosphide preparations, in
tablet, pellet, sachet, plate or strip form. E.g.:
AlP + H20 = PH3 + AlOH. Phosphine
is a light gas (only slightly heavier than air)
with a small very active mobile molecule.
It has a wide spectrum of activity, but is a
slow-acting fumigant on insects, needing
days, rather than hours of exposure in most
situations. It will easily leak out of all but the
best-sealed enclosures, can damage through
corrosion – silver phosphide - delicate silver,
gold & copper fittings (e.g. computer equip-
ment and switch boxes) and, if the loose
pellets and tablets are used, leaves powder
deposits of (mostly) aluminium hydroxide.
Residues of the gas itself are almost impos-
sible to detect in the commodity following
normal aeration after treatment, but the dry
powder residue is usually an unacceptable
contamination in dry foods, so a “contained”
formulation should always be chosen to
facilitate complete removal [see later in this
paper for illustrated examples].
Due to the corrosion risk when the gas
is in contact with copper gold and silver,
phosphine is not normally used for build-
ings (electrical systems and computers) and
never for aircraft (electronics). With great
care it can be used in mills, by separating the
gas from all computer-activated machinery
– shrouding and separating with well-sealed
polythene enclosures – almost the exact
opposite of the fumigation procedure, where
gas leakage is the big potential problem.
Phosphine is not therefore a complete
replacement for methyl bromide in all cir-
cumstances. It also has a fire hazard poten-
tial when very high concentrations occur
– the critical auto-ignition level is 1.8% which
equates to 18,000 ppm – significantly higher
than would occur in normal fumigations.
Concentration x Time [CTP]
One of the most important features of
all fumigations is the need to contain the gas
within the fumigation enclosure at a specified
concentration for a specified time (= the
exposure period). These two factors can be
varied within limits, provided the necessary
concentration x time product is achieved.
This value (the CTP) varies according to the
pest species and live stages, and for mixed
species infestations it will be necessary to
chose the highest value quoted for the most
“difficult” species. For Methyl Bromide this
was a critical feature to achieve good kill
and not cause excess bromide residues. But
phosphine does not have these problems.
It is much more common simply to decide
the dosage, and measure the end-point
concentration.
Commodity fumigation in a
warehouse
If the store floor is in poor condition,
it will be necessary to stack on a base or
ground fumigation sheet. This can later be
drawn up, rolled and joined (clips, clamps,
glue or tape, according to the sheeting in
use) to the main stack fumigation sheets.
Since sealing is so vital to long-exposure
phosphine fumigations, it may be difficult,
or even impossible, to successfully fumigate
normal warehouses, where the ridge is
usually out of reach for any form of sealing.
Ventilated silos and bins are frequently fitted
with aerated steel floors which, again, are
almost impossible to seal to form a gas-tight
enclosure suitable for phosphine..
Not only this, but there are many grain
stores which are just not suitable for fumiga-
tion. In the days of 24-hour methyl bromide
use, it may have been possible to achieve
sufficient gas concentration to give a good
kill. 5 to 15 day phosphine fumigations may
not be possible, and it really is essential that
the fumigator-in-charge makes this clear to
the potential client
Building fumigations (= ‘space
fumigation’)
The principles under which whole build-
ings are fumigated are the same as for
stacks: the gas must be contained at the
correct concentration for the required time
(exposure period) to allow the gas time to
Spraying beetle-proof mesh – no gloves Hot-Fogging tobacco warehouse
Smoke generator Spray grain store roof ; note lake of spray
fallout for next grain to sit on
Thick bubbles of tablet de-activation
Real bulk grain fumigation – only the doorway was sheeted to the ground!! *
Spraying beetle-proof mesh – no gloves Hot-Fogging tobacco warehouse
Smoke generator Spray grain store roof ; note
fallout for next grain to sit on
Thick bubbles of tablet de-a
Real bulk grain fumigation – only the doorway was sheeted to the ground!! *
Tabs in first few minutes
100 AlP sachets in one roll – the original bag-blanket – quick and easy no masks
required legally at the time! Bulk grain with cover sheet ready to pull over. *
Bulk-bag of costly seed fumigated with PH3-no
risk
Some General Features of Fumigation
Advantages: Disadvantages:
Very penetrative into insects and
mites, into food residues and
spillage, through packaging
and into foodstuffs and other
materials, e.g.: timber
Insect and mite tolerance to
fumigants is reduced at higher
temperatures
Concentration, or time, can be
varied, within limits, providing
the final CxT product is sufficient
for the species to be controlled
High risk of gas leakage out of
fumigation enclosures over long
exposure
Sealing and good condition sheeting
is essential
Overdosing of MeBr would kill
fresh plant produce and cause high
bromide residues. Phosphine does
not have these problems
No residual protection, therefore not
a prophylactic treatment
Gas distribution affected by
stowage, temperature, absorption,
commodity etc
All involved must be trained to wear
protective respiratory protective
clothing. Not very expensive but
vital for survival
Measurement of gas concentrations
throughout the fumigation is
essential – check on instruments and
detection tubes available
Tabs in first
few minutes
Spray
grain
store
roof ;
note
lake of
spray
fallout
for next
grain to
sit on
Real bulk
grain
fumigation
– only the
doorway
was
sheeted
to the
ground!
32 | March - April 2014 GRAIN&FEED MILLING TECHNOLOGYF

5. e lake of spray
n
activation

6. search out and kill the target pest. Sealing
buildings is laborious, time-consuming (up
to 2 days full work for a flour mill), and it
will be necessary to do some pre-cleaning
of machinery to ensure good penetration
of the Fumigant
But the gas at least changes - we men-
tioned Sulfuryl Fluoride earlier – this is
now the gas of choice for whole buildings.
A Dow AgroSciences gas, supplied and
used according to DAS safety and training
standards.
The quantity of gas needed for a mill
could be considerable (usually several
tonnes) and this will require careful planning
to ensure safe de-gassing, or ventilation.
Where phosphine can be filtered out using
a mask and filter, SF cannot, so breathing
apparatus is required, with the attendant
training and understanding.
All fumigations may leak gas, despite
careful precautions. The success of the
treatment will depend on knowing that the
correct dosage has been used, and retained,
throughout the fumigation exposure period.
Taking gas concentration readings, using
simple gas-detector tubes or electronic
instruments or, in the case of SF, specialist
equipment will be needed to monitor this.
As SF is a cylinderised fumigant, additional
gas may be introduced during a fumigation
to “top up”, if leakage has occurs which can-
not be fixed. Of course, reasons for leaks
should be investigated; holes, tears and poor
sealing should be repaired urgently where
they are accessible.
Is fumigation necessary?
Fumigation is never a low-cost treat-
ment. Although it has distinct advan-
tages over other forms of pest control (for
example, its ‘seek and kill’ of insects hidden
within foods), it will not guarantee zero re-
infestation. As with all forms of chemical
pest control, there should be a justification
for the use of pesticides. How does one
justify the fumigation of food commodities?
Interestingly, since Methyl bromide has
disappeared, and SF is so relatively costly,
many mills have adopted extra hygiene
measures, and sometimes heat treatments,
to achieve a similar degree of pest control.
But, whilst fumigation and heat treatments
have no prophylactic role, targeted hygiene
does!!! So removing methyl bromide has
had the effect of minimising the use of fumi-
gation in mills, and simultaneously encour-
aging a much more hygiene-conscious mill
industry (though this industry may not see
it quite like that!!)
Acheta’s Fumigation Handbook
Whilst I justify covering quite a bit of the older techniques (liquid fumigants, for example) because
many older fumigators don't realise why they are no longer available, it also helps to put phosphine
into perspective, and hopefully it will make all think twice - we have no other fumigant gases left if
phosphine is pulled due to bad/unsafe practices. It can also take the place of the very old and out-
of-date BPCA Fumigation Manual, which also covers many of the older fumigation methods, and is
therefore also a source of historical reference.
Pricing Individually @ £25, plus P&P (£3.00)
£28 inc P&P
http://www.acheta.co.uk
. Each ‘plate’ enough for 20ft container *
Tablet residue wet deactivation – wearing a mask with filter *
100 AlP sachets in one roll – the original bag-blanket – quick and easy no masks
required legally at the time! Bulk grain with cover sheet ready to pull over. *
Bulk-bag of cost
risk
Magphos Fumistrip –for large-scale fumigations. Each ‘plate’ enough for 20ft container *
Tablet residues collected for disposal *
Tablet residue wet deactivation – w
Tabs in first
100 AlP sachets in one roll – the original bag-blanket – quick and easy no masks
required legally at the time! Bulk grain with cover sheet ready to pull over. *
Bulk-bag of cos
risk
Magphos Fumistrip –for large-scale fumigations. Each ‘plate’ enough for 20ft container *
Spraying beetle-proof mesh – no gloves Hot-Fogging tobacco warehouse
Smoke generator Spray grain store roof ; note lake of spray
fallout for next grain to sit on
Water deactivation of
ALOH Zig-Zag MgP Fumistrip
Bag-blanket on grain surface
Spraying beetle-
proof door mesh
34 | March - April 2014 GRAIN&FEED MILLING TECHNOLOGYF

7. tly seed fumigated with PH3-no
wearing a mask with filter *
few minutes
stly seed fumigated with PH3-no

8. www.gfmt.co.uk
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INCORPORATING PORTS, DISTRIBUTION AND FORMULATION
In this issue:
• Researching
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• What is
Fumigation?
A technique of
pest control using
a toxic gas
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March-April2014
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