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Preventing Plant Explosions

September 19, 2010
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It happened once again: Another combustible dust explosion.

A sawdust silo in Kreamer, Pennsylvania, exploded — making it the fourth such incident in this same plant in seven years.

This is likely the most explosions in one facility on record; however, dust explosions throughout the United States are far more common than many people realize.

An October 2009 Occupational Safety and Health Administration (OSHA) report says that there have been nearly 280 such dust fires or explosions at industrial sites in the past 25 years.

And, according to a 2006 study conducted by the U.S. Chemical Safety and Hazard Investigation Board (CSB), which took three years to complete, seven of these nearly 280 dust explosions were considered "catastrophic" because they involved multiple facilities and resulted in significant negative economic impacts in their respective communities.

The CSB study also reported that there have been approximately 120 fatalities and more than 700 injuries as a result of these dust explosions.

The study is also critical of OSHA, which is in charge of helping to protect employees in the workplace.

CSB reports that OSHA does not have standards specifically addressing the dust explosion problem, nor has it developed means to prevent such explosions.

Additionally, the report says OSHA training programs for compliance officers do not fully address the problem of combustible dust explosions.

Interestingly, although there have been four dust explosions in fewer than 10 years at the plant mentioned earlier, OSHA records indicate they have visited the plant during that time period, but there are no citations on record relating to the possibility of a dust explosion.

This means that plant managers and cleaning professionals serving these locations must be responsible and take steps to help prevent such explosions from occurring in the future.

The Hows And Whys Of Dust Explosions

"Most industrial facilities, especially manufacturing facilities, generate a certain amount of dust during their operation," says Michael Schaffer, president of Tornado Industries Inc. "This dust becomes airborne and then settles on surfaces high and low throughout the facility."

Although there have been explosions when only a small amount of dust has accumulated in a location, it is generally believed that at least 1⁄32 of an inch of dust covering more than 5 percent of a room''s surface is required for the possibility of an explosion to occur, according to Schaffer.

Possibility is the key word here because dust is just one element — the combustible material — necessary for a dust explosion.

In order for an actual explosion to occur, a "fire triangle" is required.

The other elements of the fire triangle are heat and oxygen and, when combined with other factors, these elements amalgamate and create a "dust explosion pentagon."

Managers and cleaning professionals should know there are also two kinds of dust explosions.

"One is referred to as a primary explosion and typically occurs within a specific machine or group of machines," explains Schaffer. "A secondary explosion, which is what occurred in our example discussed earlier, is when dust has accumulated on a variety of surfaces throughout a location. Typically, these explosions are worse and are harder to prevent because the combustible material, the dust, is not confined to one area."

Prevention Protocol

Professor Bill Kauffman of the University of Michigan is considered an expert on dust explosions.

He says there is only one way to prevent dust explosions: Remove the dust.

This is why cleaning and maintenance is so important and why our industry can play a key role in helping to prevent dust explosions.

But, we must be careful because it sometimes is the actual cleaning and maintenance that can help trigger dust explosions.

This is because floor areas in an industrial facility are typically swept to remove dust and debris.

Of course, in sweeping, a certain amount of the dust becomes airborne and can accumulate and contribute to a secondary explosion.

Schaffer says a better option would be to use a new generation of wet/dry vacuum cleaners with large squeegee-type wand attachments designed specifically for industrial locations.

"These machines can vacuum up and remove sawdust, cement dust and wood and manufacturing dust — as well as heavy debris and liquids when called upon," notes Schaffer.

Some systems are designed with front wheel canisters and large rear wheels to make transport in a large facility easier.

"If possible, the units should have an external filter, which is much easier to access, clean or change, and a mounted tool caddy for optional tools, attachments and other cleaning supplies," adds Schaffer. "The vacuuming option can remove the dust while keeping it from becoming airborne, effectively removing it from the floors, the largest area in the plant."

Other housekeeping steps Schaffer recommends include inspecting and cleaning high and low areas throughout the plant.

Further, plant managers must take steps to keep dust away from ignition sources — often electrical devices.

Dust-tight enclosures and other types of devices are available that help seal electrical connections, helping to prevent ignition.

"Finally, managers must conduct workforce training and education programs for all workers, instructing them on how dust explosions occur," Schaffer says. "This way, they are more aware of the problem and of steps they can take to prevent explosions."

Dawn Shoemaker is a freelance writer for the professional cleaning and building industries.

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