I worked for a very large grain company for about 30 years, and managed a number of large grain handling facilities. In that time frame, our company lost several people in “grain engulfment” accidents.
I walked on top of the grain in 100s of bins of wheat, corn, soybeans, milo, barley and oats. That is safe to do, from a grain engulfment standpoint, IF you have the gates at the bottom of the bin locked so they can not be opened, and if the grain is not somewhat deteriorated and hung up above you.
If you go into a bin on top of the grain, as the grain is being drawn out of the gates on the bottom or side, you have a pretty high risk of being engulfed and suffocating.
Unfortunately every year, several people continue to learn a hard lesson.
