How Long Until a Sealed Grain Bag Runs Low on Oxygen? Infestation Density Sets the Clock in Hermetic Storage

Hermetic bags protect stored grain because insects sealed inside consume the oxygen in the intergranular air faster than it can be replaced. How fast depends on how many insects there are, and this study computes the dependence for a 100 kg bag of cowpea with about 53 L of air space, an adult bruchid oxygen consumption of 0.055 mL per hour, and a design criterion of 5 percent oxygen. At a light infestation of 2 insects per kg the bag takes 30.8 days to reach 5 percent (37.0 days with a 20 percent margin); at 20 per kg it takes 3.2 days; at 0.5 per kg, 111.5 days. Grain alone, with no insects, would need about 878 days, which shows that the insects deplete their own atmosphere and that a clean bag gains little protection from depletion itself. The originated rule is a minimum sealed period set by the infestation seen at bagging: at least five weeks for light infestations, and a warning that a lightly infested bag opened early has received almost no protection at all. This study is simulated, not measured. SIMULATED, NOT MEASURED.