Dust Explosions in the Food Industry, Fact or Fiction?

It is quite common to hear a refrain along the following lines: “We don’t feel that there is a dust explosion risk at our plant because we have been operating for 20 years and have never had a problem.” Yet according to information released by FM Global, the largest industrial insurer, the food processing industry experiences the second largest number of losses compared to all other industrial segments.

In a recent 10-year period FM reported 18 losses in the food processing industry with an average loss of almost $400,000 per claim. In another 10-year period, the same company reported 12 losses with even higher per loss costs, but they also point out that their loss statistics reflect only a small part of the total losses for industry. Getting an accurate picture of the true risk of loss due to dust explosions is extremely difficult because companies often sustain losses that are below deductibles, and in all cases there is a reluctance to go public with what is clearly a negative experience. Public image, litigation, unwanted regulatory scrutiny, fines, increased insurance costs, all inhibit any desire to talk about this subject.

Periodically a spectacular dust explosion makes the news. Last fall, for example, there was a dust explosion at Hormel Foods that sent 5 people to the hospital, at least one with serious injuries. More recently, we have all become aware of unfortunate dust explosions in North Carolina and Kentucky. Beyond the human tragedy of serious injury or even death, there is the loss of livelihood with forced plant closures, loss of revenue, costs for reconstruction and so on. The actuarial value used to assess the fiscal consequences for the loss of one life in an industrial accident is $1,000,000. One fortune 50 corporate manager told me that the real cost used internally at his company is ten times that value. Clearly life safety issues go beyond mere dollars, but irrespective of the value placed on life, there is a growing awareness that losses of this kind must be avoided whenever possible. No responsible manager wants to appear uninformed, much less negligent in matters of this gravity.

So, for the decision-makers at my hypothetical food plant that have not yet had a dust explosion experience, how do they determine if they are at risk? One useful reference point is to look at the causes for dust explosions. The NFPA Explosion Handbook provides some useful information. Mechanical sparks ignited 26.2 % of dust explosions in one study, and 4.6% in another. Smoldering nests, 11.3% and 13.6%. Mechanical friction, 9.0% and 22.7%. Electrostatic discharges, 8.7% and 0%. Fire, 7.8% and 9.1%. Spontaneous ignition, 4.9% and 0%. Hot surfaces, 4.9% and 9.1%. Cutting/welding, 4.9% and 6.8%. Electrical equipment, 2.8% and 15.9%. Unknown or others, 19.5% and 18.2%. Is there a modern food processing plant that does not have one or more of these?

Another way to look at the risk for dust explosions is to look at the types of dry bulk ingredients that are being processed. In a broad sense any organic dust, handled in large quantities, posses a risk. A very short list of examples of well known agricultural dusts that have fueled dust explosions in the food processing industry include: Milk powder, sugar, starch, fructose, flour, whey, cocoa, and malt. Flavorings are a mixed bag, obviously salt is inorganic and does not burn, but organic based spices and flavorings can be quite reactive. Some food additives such as threonine are particularly ignition sensitive. If you are unsure, the best thing to do is to have your dust(s) tested.

FM Global reports that the greatest number of losses in the food processing industry have occurred in bucket elevators, silos, bins, and dust collectors. Other equipment with the potential for significant loss includes dryers such as: Drum, fluid bed, and spray types. Equipment that imparts a lot of kinetic energy to the product is a good candidate for trouble including: High-speed mills, grinders, blenders, and mixers. Vibrating screeners can be the location for losses if, for example, bonding is lost between the vibrating screen and the stationary housing; and where the dust has a very low ignition energy such as fructose or some food additives.

A simple example of how to put all this information together might be helpful. Sugar is size reduced in a grinder, with the fine powder then transferred via conveyor to a filter receiver. Here several factors indicate that there is risk for dust explosion.

Often, there is little appreciation for the increased risk posed by fugitive dust, that is dust laying on the floor or on “I” beams etcetera. In a typical event, a primary explosion occurs inside a vessel that results in breach of the vessel. The escaping pressure wave hits fugitive dust and lifts it up into a cloud. The flame ball that emerges through the breach then ignites the suspended dust cloud in the room and a secondary explosion ensues. Very likely this secondary event will be far worse than the initial explosion. So, walk through your plant and look for fugitive dust. If inspection reveals that there is a layer of dust the thickness of a paperclip, you have a problem.

The proper assessment of risk really requires the help of a qualified professional. Dust explosions are not only rare events, but they are highly complex and extremely difficult to predict. If you are handling large quantities of organic dusts such as those mentioned, have any of the types of equipment discussed, and recognize the presence of one or more of the common causes for ignition, then you probably do have a risk. Realize too, that dust explosions are typically over in 100 milliseconds or less. There is no time for people to react; such as would be the case in the event of fire. Couple this concern with the sizeable losses commonly reported, and it is should be possible to assess your exposure and make an informed decision about the need for professional consultation. If you remain unsure of your situation, then it would be better to err on the side of safety and hire a qualified explosion consultant to evaluate your process, the inherent risks, potential consequences, and make appropriate recommendations. Finally, if you get an opinion that you don’t like, get a second opinion if necessary, but whatever you do, don’t ignore the risk. The potential consequences are not in your favor, and the food processing industry has historical loss data to substantiate that statement.

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