What is Dust Explosion?
Combustible dust explosions are usually referred to as either a primary or secondary explosion. A primary dust explosion is one that occurs inside a process vessel such as a dust collector and the fuel is usually the actual process dust. Secondary explosions often follow a primary explosion. Essentially, the pressure wave from the primary explosion lofts fugitive material that was previously deposited on overhead surfaces.
The lofted material then forms a cloud and eventually finds an ignition source resulting in a secondary explosion. One of the more well-known dust explosions was the incident that occurred at Imperial Sugar where a series of secondary explosions demolished the facility causing over $270 million dollars in damage.
Five things to keep in mind when handling dust:
- Understanding the characteristics of the dust is first. It is difficult to develop effective combustible dust prevention and protection strategies without understanding the ignition sensitivity and explosion severity properties of the dust that may be present. Laboratory testing provides the foundation needed to develop those strategies.
- Controlling ignition sources comes next. Some ignition sources may be obvious (e.g., open flames, heated surfaces) but others are more subtle (e.g., static electricity, friction caused by misalignment, inadequate maintenance).
- Fuel deprivation – a cousin to housekeeping – is an often-overlooked need. For the most part, housekeeping is performed after combustible/hazardous dust has been released. Fuel deprivation is focused on upstream identification and control of combustible dust sources before the release occurs. Examples of fuel deprivation “opportunities” include enclosing transfer points, installing local exhaust ventilation, and redesigning/replacing leaking seals.
- I do not think that the risk of flash fire can be underestimated. Providing properly rated fire-resistant clothing (FRC) for “at risk” workers can be critical.
- Conducting a DSEAR and flammability testing to gauge the extent to which the hazard is present in the plant and formulate a “to-do” list on how to reduce the risk of an accident.
As process safety consultants we are often engaged to undertake Process Safety Audits and DSEAR Assessment on behalf of or with our clients. The assessment is, of course, a thorough, orderly, systematic approach to identifying, evaluating, and controlling hazards of process.
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