Jefferson, Iowa, was the unfortunate host of a grain elevator explosion on May 2 and on June 1 there were two more explosions at separate elevators in Minnesota; Sleepy Eye and New Ulm. Fortunately, there were no fatalities in any of these incidents but these events could have happened anywhere. What is your grain elevator doing to ensure the same does not repeat? Perhaps now is as good of a time as any to start a discussion of what practices are best to keep people safe and silos standing.
In this article, we will discuss what causes a grain elevator explosion and what are some preventative practices that minimize the chance of grain dust igniting.
According to an OSHA report, there are five conditions to meet to have a dust explosion, they are oxygen, heat, fuel, dispersion, and confinement. These five factors make up what is known as the Dust Explosion Pentagon (look in the top right for a visual).
Oxygen is pretty self-explanatory; you need air for a flame to occur. Heat can be anything that would ignite the dust in the first place, such as hot machinery, metal scrapping, or friction/static electricity. Fuel is the dust and it can be from grains like wheat, oats, and rice. Dispersion is the previously mentioned dust becoming suspended in large quantities, in a confined space. The confinement is an enclosed area - think elevator leg casing or a basement tunnel.
During a dust explosion, two phases occur:
Phase 1 (The flashpoint): This is the initial blast. Explosions most commonly occur at a transfer point; these can be bucket elevators or enclosed conveyors. The dust becomes dislodged at this point due to the fast-flowing mechanical parts - one bushel of grain weighs around 50 lbs. and if a 12,000 bushel per hour leg is working all day long - that gives way for a lot of dust to become suspended. That suspended dust then comes in contact with an ignition source and the inaugural explosion occurs, completing phase one of the dust explosion
Phase 2 (Chain reactions): The first explosion will send out shock waves that dislodge static dust that has been resting on the floor, shelves, rafters, etc. which causes that dust to be suspended in the air which is then ignited by the flame and heat of the initial explosion. Phase 2 will often contain multiple explosions as each explosion will cause another. This chain of events can happen so quickly that it might seem as if there is just one very large explosion. It is important to note that these explosions are unpredictable and can be more destructive than the first explosion.
Believe it or not, there does not need to be very much dust to cause the initial explosion that we see in phase 1. The minimum explosion concentration (MEC) is 0.002 inches to 0.004 inches in a two-foot enclosure, for reference, a single piece of paper is 0.004 inches thick. The optimum explosive concentration (OEC) for the same enclosure is 0.02 inches to 0.04 inches. The following is a table that converts the MEC and OEC of different enclosed spaces:
As you can see, it does not take much dust to have an explosion, and interim, meet the conditions for the Dust Explosion Pentagon.
In a perfect world we would be able to mitigate all risks of an explosion, but since we cannot, here is a very short list of preventative measures developed by Oklahoma State University, OSHA , and Karl von Knobelsdorff that you and your staff should be following minimize risks:
Having effective systems and sanitation programs can be expensive and take up a lot of time but the loss of production, structural damage, and even death will cost much more.
Make sure that companies you hire to install electrical systems have experience doing that very thing. Companies like Knobelsdorff design and implement specialized electrical and controls systems for some of the biggest plants and have staff who are up to date on their knowledge of National Fire Protection Agency (NFPA) guidelines and National Electric Code.
Putting the safety of your employees and customers should always at the first thing that your company considers when making any decisions, take time to make sure that your grain elevator is doing everything that can be done to prevent explosions.
To start a conversation with an expert at Knobesldorff.