(84b) Ignition Sources Are Free: A Discussion of Common (and uncommon) Ignition Mechanisms for Gaseous Fuels and Combustible Dusts

Fires and explosions occur when a fuel and an oxidizer are subjected to sufficient heat to initiate an uninhibited chemical chain reaction (typically combustion). A source of heat capable of initiating this reaction is known as a competent ignition source. The competence of a potential ignition source depends on the fuel, the oxidizer, and the circumstances in which they are exposed to the source of heat. Ignition sources that are competent for common fuel gases may not be competent for common solid fuels, and vice versa. Additionally, an ignition source may only be competent for a fuel in a particular form and incapable of igniting the fuel if fuel parameters are modified (e.g., size, composition, moisture content, phase).

The built environment is well-supplied with sources of heat energy capable of igniting gaseous fuels and combustible dusts. This is especially true in concentrated industrial sites common in the chemical process industry. Thus, the well-known process safety professional Trevor Kletz is often quoted as stating, “Ignition sources are the only thing we get for free in the chemical industry.” However, sometimes assuming an ignition source exists is not enough, and instead the available sources of heat must be evaluated relative to the fuel, oxidizer, and proposed ignition scenario that brings all the necessary elements together in the necessary form, location, and time to result in ignition. For example, the competence of an ignition source is a critical element of many ignition source control strategies as well as post-incident fire and explosion investigation.

This presentation addresses circumstances where one or more competent ignition source(s) must be identified, either before a fire or explosion has occurred for the purposes of prevention, or afterwards for the purposes of incident investigation. Case studies examine common and perhaps less well-known ignition sources and the systematic comparison and refutation of ignition scenario hypotheses in support of a scientific fire or explosion investigation.