Lurking in many manufacturing plants is a danger that has been ignored for far too long. It can't be smelled nor heard, and often it can't even be seen, but it can strike without warning with devastating impact on many types of facilities ranging from granaries to chemical plants. The threat is combustible dust.
You need not look far to see how costly combustible dust incidents can be. On February 7, 2008, employees at the Imperial Sugar plant in Port Wentworth, Ga., learned this first hand when a dust explosion killed 13 people and left several others critically injured. The greater tragedy was that such a disaster could have been prevented.
When most people think of explosions, they think about TNT, gasoline and other highly combustible materials - but not about dust. The fact is that most organic substances - including wood (cellulose), polymers, food products and some metals - can explode when suspended in a dust cloud and when conditions are right.
Explosions are caused by the simultaneous presence of three factors: fuel in a powder or gaseous form, such as sawdust, flour or any substance that can be burned; an oxidizer, such as oxygen; and an ignition source, such as an open flame, a spark caused by friction or an electrostatic spark. If all three elements are present at the same time, an explosion may follow.
Although rare, dust explosions can be fatal or result in serious injury. At a minimum, they can destroy equipment and disrupt business operations. Whether the powder is wheat flour or a granule chemical product, the potential for an explosion is real, and must be recognized and avoided.
The U.S. Chemical Safety Board (CSB), an independent federal agency charged with investigating industrial chemical accidents, has been concerned about dust explosions in recent years. In 2003, the board investigated three explosions: one at West Pharmaceutical Services in Kinston, N.C., where plastic powder that had accumulated above a suspended ceiling exploded, killing six and injuring many others; one at CTA Acoustics in Corbin, Ky., where phenolic resin exploded, killing seven and injuring others; and one at Hayes-Lemmerz in Huntington, Ind., where aluminum powder exploded, killing a worker.
After investigating these three explosions, the CSB commissioned a study on the extent of the industrial dust explosion problem. The board identified 281 fires and blasts over a 25-year period that killed 119 workers and injured 718. It found 24 percent of these incidents took place in the food industry.
In its report, the CSB noted many of the incidents could have been avoided if applicable consensus engineering standards had been followed. Many of these standards, which are published by the National Fire Prevention Association, are also recognized by the Occupational Safety and Health Association, which last year issued a national emphasis program on combustible dust that directs its field offices to inspect facilities that generate and handle combustible dusts. In the near term, however, it will be up to individual companies to be prepared by being proactive.
What can manufacturers do? First, they must know if the materials they handle are combustible dusts. In most cases, this means the material must be tested according to OSHA-prescribed methods. Experience has also shown that proper design of powder handling and processing equipment is the best approach to preventing and/or mitigating dust explosion hazards. It's important to involve employees in regular process hazard reviews, during which handling procedures and protection measures can be challenged and refined.
Finally, a simple and effective step that facilities can take to prevent dust explosions is to employ good housekeeping practices such as avoiding excessive or unnecessary shaking when emptying a container, cleaning up spilled materials immediately and avoiding the accumulation of dust or powdered solids in the workplace.
Unfortunately, most companies aren't staffed or trained to conduct regular safety training sessions, assess compliance or implement solutions in accordance with engineering standards. Firms that don't know where to begin should consult an expert. As a start, look for a partner with manufacturing experience — one that participates in industry forums like NFPA and ASTM and works closely with government-sponsored initiatives associated with dust explosion and reactive material hazard assessments. This will go a long way toward proactively addressing potential hazards, avoiding costly citations and preventing business interruption.
Dean Hamel, Larry Floyd and Tom Hoppe are leaders with Ciba Expert Services.
To learn more, visit www.ciba.com or call 251-436-2397.