Embed Size (px)
Citation preview
Dust Hazards – Inherent Safety
To the Editor:
Inherent Safety is an approach to process risk reduc-tion that involves the elimination or reduction of ahazard rather than the control of a hazard by admin-istrative or engineering means. Inherently saferapproaches are more reliable than administrative orengineering controls. Inherent safety can be appliedeffectively to combustible dust hazards.
The hazards of combustible dust are well knownand have been brought to the forefront by investiga-tions done by the U.S. Chemical Safety Board (CSB).CTA Acoustics, West Pharmaceuticals, and Hayes Lem-merz were involved in dust explosions that resulted infatalities, injuries, and major property damage. CSB iscurrently conducting a hazard investigation on com-bustible dusts that will explore the extent and nature ofthe dust explosion problem and make recommenda-tions to address the issue.
These incidents were caused by the accumulationof combustible dusts outside of process equipmentinside of buildings. Several approaches can be takento reduce the risk of dust explosions inside of build-ings. Ignition sources can be controlled with electrical
area classification, equipment and structural ground-ing, hot work permits, and other administrative con-trols. Ventilation can be engineered to increase airflow and reduce confinement. Explosion venting canbe engineered to control the effects of an explosion.One inherently safer approach is to implement goodhousekeeping, thus eliminating the accumulation ofcombustibles in the first place. To effectively addressthe hazard, inherently safer approaches should beused with administrative and engineering controls.
Dust hazards also exist inside process equipment.The hazard is often controlled by inerting (less than10% oxygen), explosion venting, and explosion sup-pression systems. An inherently safer approach wouldbe to design the process equipment to contain a dustexplosion (ten times the operating pressure) andeliminate the hazard of vessel failure. Another inher-ently safer approach is to avoid combustible dusts bycontrolling particle size if possible. Fine dusts are eas-ier to ignite (require less energy) than larger particles.In practice dust hazards are controlled by inherentlysafer approaches as well as administrative and engi-neering controls.
John F. Murphy, PEProcess Safety Services
Chemical Consultants NetworkPunta Gorda, FL [email protected]
� 2006 American Institute of Chemical EngineersDOI 10.1002/prs.10170Published online 30 October 2006 in Wiley InterScience(www.interscience.wiley.com).
Pharma and Semiconductor – Inherent Safety
To the Editor:The concept of inherent safety has been embraced
by the pharmaceutical and semiconductor industries.Inherent safety is based on the design of facilitiesand processes and the selection of chemicals toreduce or eliminate the possibility of an accident.Specific examples of inherent safety implementationin the pharmaceutical and semiconductor industriesinclude replacing low boiling point solvents, limitingstorage quantities of silane, and designing processingareas to contain the release of hazardous chemicals.
Implementing inherently safe designs is often associ-ated with higher initial costs arising from the design andthe technologies required. During plant design phases,
design alternatives are selected based on yield and out-put requirements, project schedule, and ongoing oper-ating costs, among other factors. However, the costsassociated with an accident or chemical release are typi-cally not included in the economic analysis during theproject’s design stage. This may result in the analysisproviding an incorrect or incomplete result. Therefore,it is important to understand the costs associated withtraditional safety approaches and the costs associatedwith inherent safety approaches. Coining a phrase, in-herent safety is inherently better because it more effec-tively manages the risk of accidents and chemicalreleases.
Brian MooreEli Lilly and CompanyIndianapolis, IN 46285
� 2006 American Institute of Chemical EngineersDOI 10.1002/prs.10173Published online 31 October 2006 in Wiley InterScience(www.interscience.wiley.com).
266 December 2006 Process Safety Progress (Vol.25, No.4)
