P. Williams, W. Minett and T.G. Amos

A bolted galvanized iron silo (21.5 t) was sealed using a polyvinyl resin formulation (1624 White) sprayed onto joints from the inside. Gastightness was assessed by pressure decay and static pressure tests. The silo was loaded with wheat into which cages of insect-infested wheat, thermocouples and gas sampling lines, were introduced. Oxygen levels were reduced to < 1 % by purging with nitrogen, and similar levels were then maintained by a slow nitrogen bleed for 35 days, after which the silo was emptied. All adult insects were dead but, as expected, some immatures survived since the maintenance period was too short to ensure complete kill at the observed grain temperatures (generally < 15¦C). The silo was reloaded, resealed and tested again for leaks. Some leaks were found and sealed with silicon rubber. Gastightness was not as good as before, though the silo would still be suitable for fumigation. Further sealing would be required however, if nitrogen were to be used efficiently (maintenance rate of 0.2 m3 t-1 day-1). Sealing achieved was sufficient to permit use of nitrogen or fumigants but sealants cost $132 and labour a minimum of $280, representing an overall cost of $19.1 6 t-1. This would still be cheaper than buying a new silo of suitably gastight construction at a cost of at least $28 t-1.