11. Term used in fumigation

Aerate	To unseal a fumigated area and allow air in and gas to escape. This is done until gas levels are low enough to allow safe reentry.
Carrier	An inert material that serves as a diluent by may provide additional benefits. Carbon dioxide added to fumigant mixtures helps suppress fires or explosions, and aids gas distribution.
Circulation	The movement of the gas within the confined space.
Compatibility	The actual amount of gas that can be measured in the free air space of a fumigated area. This will be less than the dosage due to leakage and sorption. Normally concentration is expressed in g/m3, Oz/1000 cu.ft., or in p.p.m.
CT product	The measured amount of a fumigant over a certain period of time (mg h/1) or ounce hours per thousand cubic feet. Ideally the concentration is measured each hour and the amounts are added together. It is also possible to extrapolate data from less frequent readings.
Condensation	The action when a vapour changes to a liquid form such as the condensation of water vapour from the air when the air is cooled.
Dermal toxicity	Toxicity of a material as tested on the skin. It normally suggests that the chemical passes through the skin and affects some body function. [Hydrogen cyanide will penetrate the skin readily and could be fatal even when a gas mask is worn],
Diffusion	The process whereby a fumigant moves from an area of high concentration towards an area of lower concentration. Gases with a higher molecular weight will move slower than ones with a lower molecular weight if all else is equal.
Dispersion	The movement of the gas from its point of release, i.e., passively by convection through the fumigated enclosure, and molecularly by diffusion over short distances.
Door gaskets	Rubber or plastic cushions lining the edge of doors. When these are in good condition they help give a better seal.
Dormant	A resting stage of an insect during which respiration is reduced. This is often a stage that is difficult to kill.
Dosage	The amount of fumigant introduced. Much of this will be lost due to leakage or sorption. Dosage is normally measured in g/m3 or oz/1000 cu ft.
Equilibrium	The point at which the gas concentration is the same throughout the fumigated area. A long exposure time or air circulation may be needed to achieve this. Failure to achieve equilibrium would be a sign of poor fumigation technique.
Evolve	The release of gas molecules from a liquid or solid substance. Moisture and heat are required to release phosphine from aluminum phosphide tablets but only temperatures above 39.5°F are required for methyl bromide to evolve into gas.
Fumigant	A chemical which, at a required temperature and pressure, can exist in a gaseous state in sufficient concentration to be lethal to a given target organism. This means that it will move as single molecules and can therefore penetrate through most materials other than metal or glass.
Gas proof sheet	Any cloth or plastic that by itself or with its coating can contain given fumigant gases in sufficient quantities to achieve total control during a fumigation.
Hatch	An opening or door to an area of a ship such as a hold.
Heat exchanger	A device usually containing hot water that will exchange heat with fumigant gases that are passed through. This is used to assure that gases such as methyl bromide are warmed to the point of a true gas in spite of the cooling effect that occurs when such gases are released and expand. Gases such as methyl bromide have different properties as a liquid and can cause damage that would not occur in the gaseous phase.
Headspace	The amount of space in a container above the product.
Half-loss time	The amount of time that has elapsed before one half of the gas has been lost due to leakage and sorption. This is an important measurement in relation to the remaining concentration.
Holds	The storage compartments in a ship that are below deck.
Inhalation hazard	The hazard to persons or animals from breathing in the fumigant gas. This is the principal hazard from most fumigants.
Insecticide	A chemical designed to control insects.
Intransit fumigation	A fumigation that occurs inside the transportation vehicle or container. It may occur partly while the object is stationary but the term indicates that the area was not aerated prior to shipment.
Leakage	The loss of fumigant gas through an opening in the building or the gas proof sheet.
Modified atmospheres	A change in the composition of the gases in the air in a confined and sealed structure. Normally oxygen is greatly reduced and carbon dioxide, carbon monoxide, or nitrogen is increased. Control of the insects can be due to merely the depletion of the oxygen or to the toxicity of the remaining gases at that concentration.
Ounce hours	A measurement that reflects the total exposure of the fumigant to the insect. Properly measured, it is the total of the concentration at each hour of exposure.
Penetration	The passage of a fumigant gas into or through an object such as grain, soil, or building walls.
Persistence	The quality of an insecticide to persist as an effective residue due to its low volatility and chemical stability. Fumigants are examples of pesticides that are not normally considered persistent. Exceptions would be where the fumigant was retained by cold surfaces such as cold grain may retain liquid fumigants for a period of months.
Polyethylene (Poly)	One type of plastic sheet that is used as a gas proof sheet. It is available in several thicknesses and in many widths and lengths. Light weight materials are used only once and then only inside since it can be torn easily.
Quintal	100 kg
Picul	60 kg
Release of fumigant	The introduction of the fumigant either from a cylinder or from formulations that will cause the gas to evolve.
Residue	The amount (often a trace) of a pesticide and its metabolites left in the food crop after treatment.
Residue tolerance	An amount set by a government that they will permit of a residue in a food crop. It is an amount that they believe will not harm the consumer based on the toxicity and the percentage of that food in the normal diet. It is often set at 1/100 of the amount that can produce a symptom of any kind in a person. It is always as low as good practice will permit even if a higher amount probably would not hurt anyone.
Resistance (insecticide)	Ability of an organism to tolerate the normal concentration and time of a pesticide such as a fumigant. A 10' fold resistance would mean that 10 times as high concentration might be needed. Resistance is usually the result of poor control that has allowed only the least susceptible individuals to breed with similar individuals. This selects for increased resistance.
Sachet	A package of fumigant designed to release the gas hut retain the remaining dust. Sometimes called a bag.
Sanitation	A programme of cleaning and maintenance designed to deny food and shelter to specific organisms. Removal of old or spilled grain would be an example of one small part of a Sanitation Programme.
Sealed	The enclosing of an area so that the gas cannot escape too quickly. It is recognized that a certain amount of leakage will occur on even the best fumigations hut this needs to be held to a minimum.
Self Contained Breathing Apparatus	A mask that tightly covers the entire face and has breathing air supplied from a compressed air tank carried separately, usually on the back.
Shooting hose	A hose that is connected to a cylinder and then placed inside the sealed area that is to be fumigated. It is a means to transport the gas from the cylinder to the fumigated area.
Space sprays	Pesticides that are dispersed temporarily in the air where they will stay suspended for a short period of time. They are designed primarily to kill flying insects but can kill others exposed insects as they mist settles.
Sorption	The total uptake of gas resulting from the attraction and retention of the molecules by any solid materials present in the system. This can he a significant reason for gas loss.
Stacks	A series of bags of grain placed on top of each other in an orderly fashion.
Tarpaulin (Tarp)	A fabric used to cover an object. This term is sometimes used to indicate gas proof sheets but it is also used to merely indicate waterproof sheets. To avoid confusion, use the term gas proof sheets.
Tape	A strip of cloth, paper, or plastic with adhesive on one or both sides. It is often used in fumigation to seal small cracks. It will stop the airflow if it does not come loose but tests show that most tapes are readily penetrated by fumigant gases.
Vapour pressure	The pressure exerted by a gas that is in equilibrium with its solid or liquid state. This would indicate it is more volatile if it has a high vapor pressure.
a.i.	Active ingredient.
ft³/sec	Cubic feet per second.
m³/sec	Cubic meters per second.
G	Grams.
g/m³(gm3)	Grams per cubic meter. HEHous exposure.
HLT	Half loss time.
m3	Cubic meters.
p.p.m	Parts per million.
p.p.b.	Parts per billion.
SCBA	Self contained breathing apparatus.
°F	Degrees fahrenheit.
°C	Degrees centigrade.
met"	1000 cu ft.
%w/w	Percent weight/weight.
%w/v	Percent weight/volume.

g/m³ Phosphine x 658.8 = ppm
ppm - 10,000 = % by volume in air
g/m³ methyl bromide x 235.9 = ppm
oz/1000 cu ft = g/m³ = mg/liter (approximately)
1b/1000 US bu x 12.87 = g/m³
1 g/m³ phosphine = 659 ppm = 28.5g/1000 cu. ft. = 33g/1165 cu ft

In practical terms, the above conversions are indicative only. For more accurate conversions, temperature and pressure are important. For example, at 25°C and 760mm.,

g/m3 (g.m^-3) Phosphine x 718 = p.p.m.
g/m3 (g.m^-3) Methyl bromide x 257 = p.p.m.