Infestation inside grain silo is not something which people are not aware of. Infestation does happen inside silo and Fumigation must be carried out to kill pests and insects etc. to save the grains inside silo. Most insects enter grain silos from the top and stay there within 1-2 meters for weeks.
Fumigation is a most essential activity for safe storage of grain inside silo. Grain storage silo must have a properly designed fumigation system.
Fumigant
Phosphine or Hydrogen Phosphide (pH3) is most commonly used fumigant to kill pests in grain silo. Phosphine or Hydrogen Phosphide (pH3) is available in solid form and emits phosphine gas. Phosphine is an inexpensive gas and not an ozone depleting gas, hence considered environmentally safe. Pure phosphine is odorless however due to impurities it smells garlic like or decomposing fish. Phosphine has a density of 1.45 Kg/m3 at 15 DegC. Phosphine gas may self ignite at concentration over 17900 ppm hence it must be handled carefully. Exposure to humans more than 0.3 ppm is not at all advisable. Metals like copper, gold, silver, and brass must not be exposed to phosphine gas as it reacts with them.
Fumigation System
There are various methodologies of grain fumigation inside silo. The most common and economical one is Closed Loop Fumigation system. Closed loop fumigation system consists of Gas Fan, uPVC Pipes, Inlet Outlet Valves and Electronic Gas Monitors. Silos must be properly sealed before initiating fumigation of silos to minimise fumigant leakage during fumigation.
However to have effective fumigation Gas fan, Nos of gas changings per day and uPVC ductings must be sized properly based on size of Silo.
Fumigant Dosage
In order to kill grain pests at all stages of their life cycle (egg, larva, pupa, adult), including pests with strong resistance, phosphine gas concentration levels need to reach and be maintained at 300 parts per million (ppm) for seven days (when Grain is above 25°C) or 200ppm for 10 days (when he grain temperature is between 15–25°C). Partially killing pests is worse than not killing at all as then they generate resistance to phosphine and are difficult to kill.
Once the fumigation cycle is over, Silo must be de-sealed and aeration fans must be kept running until the Phosphine levels drop down to 0.3ppm. Phosphine monitors must be used to check the levels of Phosphine.
Precautions while fumigating with Phosphine Gas
Phosphine is toxic to Humans and Animals beyond permissible exposure limit of 0.3 ppm. While doing fumigation, never eat, drink or smoke. Wear Dry clothes and Dry Gloves.
Besides, Keep phosphine gas away from the following;
·     Battery and Battery Chargers
·     Electric Motors
·     Computers
·     Electrical Switch Gears
·     Electronic and Electrical equipment
·     Metals like Gold, Silver, Copper, and other Copper Alloys etc.
Precautions ensures SAFETY hence we must follow rules while fumigating with Phosphine.
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