The Principles of Fumigation

Understanding the technicalities

Fumigation is one of several approaches, which can be used to provide an insect free environment.

What are fumigants and how do they work?

Fumigants are gases, which are toxic to the target infestation. They can be applied as gas, liquid or solid formulations, but after vaporisation from liquids or reaction products from solids, always act in the gaseous phase.They act either as respiratory poisons or as suffocants in the case of controlled or modified atmospheres.On release, they mix with air as individual molecules.This is why they are capable of rapidly diffusing from one area to another and through commodities and buildings.

Fumigants should not be confused with smokes, which are solid particles of air, or with mists, aerosols or fogs, which are liquid droplets, of various sizes, in air.Smokes, mists, aerosols and fogs are not fumigants as they are unable to diffuse (i.e. They do not mix with air as individual molecules) and reach deep-seated infestations in commodities and structures.

If it is not a gas it is not a fumigant.

Aim of Fumigation.

Fumigation aims to create an environment, which will contain an effective concentration of fumigant gas at a given temperature, for a sufficient period of time to kill any live infestation.Both the time of exposure and the concentration of gas are critical to fumigation efficiency. Dosages are therefore usually expressed as grams per cubic metre, and target concentrations or concentrations actually achieved, as Concentration Time Products (CTPs).

Concentration Time Products (CTPs)

CTP is a measure of the effectiveness of fumigation.The CTP at any point within the fumigation enclosure is a product of the average gas concentration (g/m3) multiplied by the total time of exposure (hours).The CTP will vary at different locations unless there is a perfectly even distribution of gas.If the CTP relates to the established insect toxicity data, a fair assessment of success can be made. In the case of phosphine, time of exposure and temperature are also very important.The CTP is expressed as milligram-hour per litre or gram-hour per cubic metre.

The critical parameters that need to be considered for fumigants to be effective

• Nature of infestation
• Type of fumigant applied
• Concentration and distribution of gas
• Temperature
• Length of time fumigant must be applied for
• Method by which fumigant is administered
• Containment of fumigant
• Nature and quantity of commodity
• Nature of commodity packaging
• Monitoring system