Grain elevators are made to handle large volumes of grain. The buildup of grain dust in the handling process is unavoidable. There have been over 500 grain dust explosions in the last 35 years in the United States. They have killed more than 180 and injured more than 675 people. There are four elements required for a grain dust explosion are the presence of dust, confinement and enclosure, oxygen, and an ignition source. Most of the time in a grain elevator, the first three of those are present. The grain dust comes from particles falling off of wheat, oats, barley, or other grains. It is confined because the silo walls trap it. Oxygen is always present in these structures. The last thing needed to cause the explosion is an ignition source. The ignition sources could be caused by static electricity. This becomes possible when the humidity becomes low. Dry environments cause static electricity to accumulate. Cutting, welding, brazing, and overheated motors are also common sources of ignition (Grain Handling https://www.osha.gov/SLTC/grainhandling/index.html). Other ignition sources could be mechanical friction caused by faulty moving parts. For example if you have a conveyor belt with bad bearings the friction in the bearing produces heat. It can be enough heat to cause a fire. That then becomes the ignition source. Keep in mind all moving parts or machines in the grain elevator have potential to malfunction. In large facilities the shockwave from a grain dust explosion can stir up dust in connected silos and combust also causing multiple explosions. This is called a secondary explosion.
As a result of many accidents over the years it is now an OSHA regulation for employers to practice good housekeeping and maintain a clean confined space to reduce the chances of grain dust explosions. The areas included under this regulation are: the inside of bucket elevators, floors of enclosed areas with grinding equipment, and floors of enclosed drying bins. The dust is to not exceed 1/8 inch of accumulation on floors, ledges, or on top of equipment. You are not to remove dust with compressed air unless all potential ignition sources are shut down (anything that can cause a spark or heat). The grain dust becomes suspended when air is used. If direct heat grain dryers are being used, they must be fitted with automatic controls to stop the fuel to it in case of a fire or explosions and must be located outside the structure or inside a one hour fire rated wall. On a leg casing the bearings should be installed externally to monitor heat to prevent them from becoming an ignition source. Both OSHA and The Federal Grain Inspection Service of the Department of Agriculture have kept very accurate records on grain dust explosions. OSHA has made and enforces these regulations as a result of previous accidents. All of these regulations are made to either prevent a grain dust explosion, prevent secondary explosions, or cut off fuel to a fire after an explosion. To prevent grain dust explosions these regulations have been made to take out one of the factors needed to cause a grain dust explosion. Oxygen, fuel, confinement, and an ignition source are all needed to cause an explosion. These regulations prevent explosions by taking out either fuel, or ignition sources. All of these regulations and standards can be found with OSHA (General industry 29CFR1910 sub part G, 1910.94-Ventilation) (General Industry 29CFR1910 subpart D, 1910.22-Houskeeping) (General Industry 29CFR1910 subpart L, 1910.157-165- fire protection and subpart E, 1910.38-exit routes, emergency action plans, and fire prevention plans) (OSHA grain regulationshttps://www.osha.gov/dea/lookback/grainhandlingfinalreport.html#II)
Sample Policy and procedure
From past accidents we have learned how to prevent these explosions. The grain elevator industry has been very productive in not eliminating the potential explosions but limiting them. They have found the causes of the accidents and then applied solutions. Here are some of the solutions that have been discovered. If you put heat sensors on bearings and moving parts the workers will be warned of the hazard and the part can be fixed before it causes enough heat to ignite the grain dust. They have found it is best to monitor potential hazards before they ignite the dust. The technology used in modern elevators is so advanced that a computer system can shut down a machine if it is causing too much heat. Another solution they have found is preventative cleaning. Most grain elevators will shut down and clean when the grain dust becomes a potential hazard for an explosion. There has been a chemical developed that is applied to an explosion and immediately suppresses the explosion. The chemical is released into the elevator immediately when a sensor detects the hazard of an explosion. The sensor is measuring the pressure in the silo and when the pressure changes to a measurement that is typical with an explosion the chemical is shot in. (Westwego Grain Elevator Disaster https://www.youtube.com/watch?v=fcc6a0zmJ48) When grain elevators are built today they are spread out instead of building all the silos close to each other. The reason for this is to prevent secondary explosions. You will also not find the offices connected to the silos.
Safety Training Materials/Videos
One of the most important steps for training employees is making sure they understand. They need to understand what combustible dust is, what causes explosions, how to prevent them, other hazards related to explosions, and what secondary explosions are. It is important that they know and understand the regulations and standards mentioned above. Employees should know the factors mentioned earlier that cause grain dust explosions. They should understand the importance of housekeeping. And most importantly they should be aware of how serious this danger is and the consequences that come with not using safe work practices. Please see videos (https://www.youtube.com/watch?v=_XLSgspBYok) and (https://www.youtube.com/watch?v=aUVnwUrja3s)