Common causes and corrections for explosions and fires in improperly inerted vessels

Abstract

In this article, causal factors and corrective actions surrounding improperly inerted vessel incidents are developed and compared based on several case studies of flash fires or explosions involving these process vessels. In industry, vessels that contain or have contained flammable vapors are commonly inerted for many reasons, but one of the most common is explosion prevention. Common inerting gases are carbon dioxide, nitrogen, steam, and air, depending upon the specific application. Incident causes ranged from procedures to design issues, but a general set has been produced for application to the problem of explosion prevention in process vessels. Each case study is compared to safety standards to show how safe work practices could have prevented the accidents. However, rigid adherence to safety standards may not be sufficient to prevent an accident. The application of a safety standard should be tempered by situation‐specific circumstances. Some specific recommendations for preventing explosions include methods for improved mixing of the inert gas, the use of blinds, filling the vessel with water, improved work procedures and improved monitoring procedures. A suggested design strategy for engineering an inerted system is presented.

Inerted vessels: Avoiding hazards caused by gas buoyancy

“…In chemical process industries, typically large inventories of hazardous chemicals stored onsite are thus exposed to the event of fire or explosion. The hazards of hot work near improperly inerted vessels have been previously documented (see Morrison, Carpenter, &Ogle, 2002, andCarpenter, 2001).…”

“…The purging and inerting of a process vessel should be based on the following simple design strategy (Morrison et al, 2002): C Specify the design objective: control fuel concentration to below the lower flammability limit (LFL) or control the oxygen concentration to below the minimum oxygen concentration (MOC).…”

“…The goal of all these documents is the same: to provide guidance on how to displace or dilute the vessel's, equipment's, or pipe's internal oxygen and/or flammable vapor concentration. Table 1 is adopted from Morrison et al, 2002, and provides an outline of the most common inerting methods and the associated applicable safety standard.…”

Optimally Safe Tank Changeover Operation Using a Smooth Optimization Formulation

“…In both cases, the operation must be performed safely so that the flammable gas/air mixture does not end up with fire or explosion; a situation that could lead to serious property or human losses, as reported in a number of case histories. 3 A safe changeover involves diluting the flammable content by an inert gas such as nitrogen or carbon dioxide such that the mixture composition is kept away from the so-called flammability zone. 1 The design of safe operating procedures is typically handled by expert plant engineers 4 that mostly rely on their experience and established techniques.…”