Lessons Learned From Fire in Air Supply Ducts

Safety and Health Division
AIChE Spring Meeting and Global Congress on Process Safety
May 1, 2013 - 1:30pm-2:00pm


Submitted for consideration to the 47th LPS on Oct 31, 2012

Title: Lessons Learned from Fire in Air Supply Ducts

Primary author: Al Waller, Principal Process Safety Engineer, FMC Corporation

A significant fire occurred inside the air supply ducts to a drying and milling operation. Investigations concluded that the interlocks functioned as designed on loss-of-airflow but were not sufficient to prevent overheating the inlet air filters (including HEPA filters) from the residual heat in the air heaters. The two main lessons learned from this incident apply to a broad range of operations in the CPI:

1) Mundane unit operations such as air filters that have combustible components must be evaluated as thoroughly as the rest of the chemical process.

2) Designers and HAZOP leaders must recognize the potential of thermal inertia of heaters (and coolers) to heat (or cool) a stagnant volume of fluid when flow is interrupted. Gas streams are particularly susceptible due to the low heat capacity relative to the heat capacity of a metallic heat exchanger. Interlocking the supplies (to steam and electrical heaters in this incident) is often necessary but may not be sufficient.

Other lessons from the escalation aspects of this fire will also be discussed.

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