(111c) Risk-Based Dust Hazard Analysis (DHA)

Fuman Zhao and Robert Weber

PSRG Inc.

800 W Sam Houston Pkwy S # 107, Houston, TX 77042

Phone: (713) 532-8800; Email: fumanzhao@psrg.com

ABSTRACT

Combustible dusts are finely divided particles that present an explosion hazard when suspended in air. Dust explosion may become more severe in a confined space, especially due to the occurrence of second dust explosion. Combustible dust explosions have caused numerous fatalities and catastrophic property damages in industries. They are now a recognized hazard that plant owners, managers, and workers cannot ignore. Many industry-specific NFPA dust standards (e.g., NFPA 61, 484, 655, 664) on combustible dust contain provisions for conducting dust PHAs. NFPA 654 applies to general combustible dusts for preventing combustible dust flash fires and explosion, which requires designing the fire and explosion safety provisions based on the dust PHA. The newest standard of NFPA 652 (Standard on the Fundamentals of Combustible Dust) became effective on September 7, 2015. It requires that dust hazards analysis (DHA) be completed on existing facilities and significant modifications before October 2018. Assessment of what can go wrong, however, may not be an easy task for dust-handling plants. NFPA performance-based dust hazard assessment and OSHA regulatory compliance requirements lack detailed guidance on how to conduct DHA. Meanwhile, standard or code-based prescriptive DHA may create redundantly unnecessary overprotection for hazard-involved dust processes and equipment. In this research, a risk-based approach is developed by incorporating both likelihood analysis and consequence analysis to define safeguard requirements for any of potential process deviations, operating upsets, human errors, and equipment failures. By comparing safeguard requirements with the credit provided through safeguard availability analysis, a risk-based DHA will provide a sufficient understanding of dust hazards, as well as the safeguard level of demand for dust process safety work activity.

Key words: combustible dust, dust hazard, risk-based approach, dust hazard analysis (DHA)