The most common hazard with grain bins is engulfment. The primary causes are moisture and grain removal. Moisture can cause the grain to stick together and form a crust at the top surface of the grain, which is known as bridging.
Bridging is hazardous because it hides underlying pockets of air in the grain. Because bridging can also prevent grain flow, workers may be tempted to enter a bin to try to dislodge the grain. Workers have then fallen though the crust and become engulfed. Similarly, moisture can cause grain to adhere or cake to the inside walls of the bin. Workers who try to knock the caked grain down can be buried as well. Grain harvested during a wet autumn, such as last fall, is more apt to bridge and cake.
Employees have also been buried in grain when they entered the bin while grain is being removed from the bottom. The employee is pulled down with and into the flowing grain. It usually takes less than one minute for a person to be completely engulfed. Carbon dioxide generated from spoiling grain can displace oxygen near the surface of the grain and suffocate an employee who is only partially buried.
The National Institute for Occupational Safety and Health (NIOSH) recommends the following precautions.
Do not enter storage bins.
Break up surface crusts from outside the bin.
Retrofit the bin with equipment capable of breaking up bridges and clumps.
If entry is absolutely necessary:
never stand on top of the stored material;
do not enter from the bottom of the storage unit when there is grain caked to the sides or bridged overhead;
wear safety harnesses or belts equipped with properly fastened life lines that will keep you above the stored material in case of a fall;
stop the flow of grain and do not load or unload the bin while someone is inside; and
turn ventilating equipment on prior to and during entry.
The OSHA requirements for grain bin entry can be found in paragraphs (g) and (h) of the grain handling facilities standard, 1910.272.
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