Miller Magazine Issue: 150 June 2022

73 COVER STORY MILLER / JUNE 2022 fumigation. When the grains are at 14% to 18% moisture level, the storage period is reduced to only 4-8 weeks due to problems of mould growth resulting in discolor- ation of grains. Below 9% moisture content, grains can be stored safely for more than one year, but it may re- sult in loss of germination. Temperature and relative humidity monitoring are the two very important aspects of grain management in- side a silo. A rate of change of temperature of more than 5.5 Deg C per week indicates that there is spoilage inside the grain silo. The respiration rate of grains increases ex- ponentially when grains start to spoil, and mould/insects develop inside the silo. An increase in respiration produc- es additional moisture, which further deteriorates the sit- uation. Hence continuous monitoring of temperature and relative humidity inside the grain silo is very important to keep the grains safe. Infestation inside grain silo is not something that peo- ple are not aware of. The infestation does happen inside the silo and Fumigation must be carried out to kill pests and insects etc. to save the grains inside the 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 the safe storage of grain inside the silo. A grain storage silo must have a properly designed fumigation system. Phosphine or Hydrogen Phosphide (pH3) is the most commonly used fumigant to kill pests in a grain silo. Phosphine or Hydro- gen Phosphide (pH3) is available in solid form and emits phosphine gas. Phosphine is an inexpensive gas and not an ozone-depleting gas, hence considered environmen- tally safe. Pure phosphine is odorless however due to impurities it smells garlic-like or decomposing fish. Phos- phine has a density of 1.45 Kg/m3 at 15oC. Phosphine gas may self-ignite at a concentration over 17900 ppm hence it must be handled carefully. Exposure to humans to 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. Grains are live, they breathe in oxygen and breathe out Carbon dioxide. This makes the atmosphere inside grain silo rich in Carbon dioxide. Carbon dioxide is acidic and when it reacts with concrete, which is alkaline. This pro- cess is called carbonation of concrete and it destroys the ability of concrete to protect the reinforcing steel from cor- rosion. It is seen that 200 mm thick concrete is carbonated in 50-years time in such carbon dioxide rich atmosphere. Minor cracks in concrete further aggravate this carbon- ation problem in concrete. Pure carbon dioxide carbonates concrete to a depth of 20-30 mm in only 4-weeks time. Never use concrete with pulverized fuel ash (A power plant by-product) for grain silo storage or foundations. Concrete having pulverized fuel ash has very low resistance to car- bonation, hence should never be used for grain silos.