Dust hazards‐inherent safety

Inherent Safety is an approach to process risk reduction that involves the elimination or reduction of a hazard rather than the control of a hazard by administrative or engineering means. Inherently safer approaches are more reliable than administrative or engineering controls. Inherent safety can be applied effectively to combustible dust hazards. The hazards of combustible dust are well known and have been brought to the forefront by investigations done by the U.S. Chemical Safety Board (CSB). CTA Acoustics, West Pharmaceuticals, and Hayes Lemmerz were involved in dust explosions that resulted in fatalities, injuries, and major property damage. CSB is currently conducting a hazard investigation on combustible dusts that will explore the extent and nature of the dust explosion problem and make recommendations to address the issue. These incidents were caused by the accumulation of combustible dusts outside of process equipment inside of buildings. Several approaches can be taken to reduce the risk of dust explosions inside of buildings. Ignition sources can be controlled with electrical area classification, equipment and structural grounding, hot work permits, and other administrative controls. Ventilation can be engineered to increase air flow and reduce confinement. Explosion venting can be engineered to control the effects of an explosion. One inherently safer approach is to implement good housekeeping, thus eliminating the accumulation of combustibles in the first place. To effectively address the hazard, inherently safer approaches should be used with administrative and engineering controls. Dust hazards also exist inside process equipment. The hazard is often controlled by inerting (less than 10% oxygen), explosion venting, and explosion suppression systems. An inherently safer approach would be to design the process equipment to contain a dust explosion (ten times the operating pressure) and eliminate the hazard of vessel failure. Another inherently safer approach is to avoid combustible dusts by controlling particle size if possible. Fine dusts are easier to ignite (require less energy) than larger particles. In practice dust hazards are controlled by inherently safer approaches as well as administrative and engineering controls.