Introduction
Fumigation is a procedure that is used throughout the world to eradicate pests that infest all types of goods, commodities, warehouses, processing factories and transport vehicles including ships and their cargoes.
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 in solid formulations, but after vaporization 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 at a molecular level. 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 in air, or with mists, aerosols or fogs, which are liquid droplets, of various sizes, in air. Smokes, mists, aerosols or fogs are not fumigants as they are unable to diffuse (i.e. they do not mix with air at a molecular level) and do not reach deep-seated infestations in commodities or structures.
The fumigant gases used to carry out the fumigation process are numerous, but the most commonly used currently for the treatment of cargoes are phosphine and methyl bromide. Others used are carbon dioxide and more
recently sulfuryl fluoride, which is starting to replace as an alternative to the prevailing fumigants.
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 infestations. Both the time measured (hours or days) of exposure and concentration of gas is critical to fumigation efficiency. The Dosages applied are usually expressed as grams per cubic metre, concentrations measured during the fumigation are usually expressed in parts per million (PPM) or grams per cubic metre, and total concentrations actually achieved, as concentration-time products (CTPs). The fumigation process is not completed until ventilation has been effectively carried out, and removal of any residues is completed.