Dust Explosions
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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. In another example, a dust explosion occurred in a large storage silo holding dried sewage sludge. The sludge was dried in a gas-fired, air-convection dryer and stored in the silo until discharged into trucks and hauled away. The silo was approximately 35% full at the time of the incident. Immediately preceding the explosion, a powered bin vent and air intake fans, had been started. The dryer was not in operation at the time of the event and had last been in operation 3 days prior to the event. The plant was cold and being started up following a long weekend. The investigation concluded that the dust explosion started because a smoldering nest in the silo was disturbed by the increased air flow when the fans and vent were started. The nest quickly transited from a smolder to a very vigorous combustion zone. The dust was disturbed into a dust cloud that reached explosive concentrations very rapidly. |
The Dust Explosion PentagonFive things necessary for a dust explosion to occur:
The concept is simplicity itself: Detect a hot body before it can ignite the dust and cause an explosion, take fast action to remove the heat, or remove the hot body from the rest of the process product. The amount of energy required to ignite a specific dust is determined by test. Many dusts will ignite explosively at temperatures well below 500ºC. To understand the concept of true infrared, think of a lighted wooden match. Upon blowing it out the temperature of the smoldering head is about 500ºC. There is enough energy in the extinguished match head to initiate a dust explosion. If such a smoldering match head were to pass by a true infrared detector in a process convey line, for example, it would be detected. Taking an action to either eliminate or quench it would complete the protection scheme. Unique technology, which in combination with our experience and understanding of process systems, addresses the ignition problem more effectively than was previously possible. Infrared hot body detectors can be used in ordinary light without triggering. The temperature limits of the detectors are low, typically 400º C, 250º C, or 175º C. These low temperatures, well below the almost 700º C threshold of spark detectors, make it possible to use this technology to prevent dust explosions. This is especially important for very ignition sensitive dusts. Older spark detection technology is not adequate in many circumstances involving today's high technology products and large-scale production requirements. While it is true that high sensitivity can be critical for adequate warning and protection against a dust explosion, all would be for nothing if the system could not distinguish a true threat from a nuisance. In other words, it would not be useful if the protection system were to trigger and interrupt production needlessly. Extraordinarily sophisticated controls ensure reliable detection without nuisance alarms. Based on the principles of movement and thermal mass, the instrumentation distinguishes a particle with high enough energy to ignite a dust explosion from sparks, which do not have enough mass to pose a credible threat. Moreover, our systems are not individual components sold in a patchwork fashion. Each system is designed from the ground up and is engineered to meet the specific requirements of the process system to be protected from a dust explosion. Taking a total system approach, careful consideration is given to each aspect of the process system including location of detectors and reaction components, control panels, and integration with the main process control system. CV Technology protects lives and preserves profits by preventing dust explosions or fires whenever possible and to mitigate the damage when an incident occurs. CV Technology combines a legacy of experienced explosion consulting with revolutionary and completely unique explosion prevention and explosion protection technologies to specialize in the prevention, protection, and elimination of dust explosion hazards in all industries which process powders and dry bulk materials. |