What happened
On 28 August 2008 a residue treater pressure vessel in a pesticide unit at Institute, West Virginia, overpressurised and exploded during the restart of the unit. The CSB reported that an interlock designed to prevent feeding process residue before the vessel was filled with clean solvent and heated to its minimum safe temperature was overridden, a principal cause; that such bypasses had happened before with management's knowledge; that the start-up began before equipment checks and the pre-startup safety review were complete; and that operator training on a new control system was incomplete. Two workers were killed and eight injured.
Lessons for SIS and instrumentation
- Permissive interlocks that enforce a safe sequence are safety functions. Treat them in the hazard analysis and give them the integrity and bypass control they need.
- Routine bypassing is a design or operating problem that must be solved, not normalised.
- Start-up readiness (pre-startup safety review, instrument checks, training) is part of the protection.
Related First Out AI articles
"Managing bypasses, overrides and start-up inhibits", "HAZOP deviation library: reactors and fired heaters", the reactor worked example (SIF-104).
Written for First Out AI as engineering guidance. It supports engineering work and does not replace it; check every value against your standards, certificates and company rules with a competent functional safety engineer.