American Petroleum Institute

Ignition Risk of Hydrocarbon Vapors by Hot Surfaces in the Open Air - Second Edition
 N PUBL 2216

Annotation

1.2 Introduction and Scope

The ignition of accidental releases of hydrocarbons in the atmosphere may result in damaging fires. Frequently, hot surfaces in the area where hydrocarbon vapor is released are assumed to be the ignition source; however, hot surfaces, even at temperatures above the published and generally accepted ignition temperature of the hydrocarbon, may not ignite the flammable mixture. Even vehicle exhaust systems, in most instances, do not operate at a sufficiently high temperature to ignite hydrocarbon vapor in the open air.[1] Experimental studies and experience have shown that hot surfaces must be hundreds of degrees above published minimum ignition temperatures to ignite freely moving flammable vapor in the open air. Whether or not flame will develop depends not only on the temperature but also on the extent of the surface, its geometry, and the ambient conditions.[2] This publication covers the technical basis for the study of ignition risk and the practical implications thereof. In particular, fire investigators should understand that ignition of flammable hydrocarbon vapor by a hot surface at published minimum ignition temperatures is improbable. Such knowledge should lead fire investigators to search diligently for other ignition sources where conditions make ignition by a hot surface questionable or unlikely.

When certain confined conditions exist, such as when oil-soaked insulation is in an unventilated, confined area, ignition of hydrocarbons may occur by spontaneous combustion at temperatures below published ignition temperatures. This publication does not include discussion of this phenomenon because the mechanism involved is different from that involved in open-air ignition.

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