Risk of gas explosion - Flammability of gases and vapors

Gas explosions in confined spaces are frequent and often spectacular domestic and industrial accidents. Gas explosions result from the ignition of a gas in an enclosure or confined space. Ignition is possible if the composition of the gas or gas mixture is flammable and an ignition source is present. The flammability of a gas mixture is therefore determined by its composition, environmental conditions, temperature, pressure, the enclosure in which it is located, and the type and intensity of ignition sources present. To avoid the risk of a gas explosion, all these conditions must be known and mastered.

Data on the flammability of fuel gases or vapors in air are often limited to regulatory data provided under standard conditions which do not correspond to the conditions of the process under consideration. However, this limited information can be used to recalculate the information required under the specific conditions of the process.

In this article, the search for flammability and regulatory data on fuel gases on the one hand, and calculation methods for adapting flammability limits in air to environmental conditions and fuel mixtures on the other, will be developed. The same attention will be paid to the study of auto-ignition in the gas phase. Before moving on to industrial implementation, direct or indirect experimental verification will still be necessary, but the experimental work involved will be greatly lightened.

Three types of gas explosion can be distinguished according to their mode of propagation and the pressure effects observed: homogeneous explosion, deflagration and detonation. The different modes of propagation of gas explosions and their prevalence conditions will be described.

When a gas phase is flammable, the question arises of the pressure effects of the explosion in an enclosure. The information characteristic of deflagrations is the maximum explosion overpressure P _max (bar G) and the violence of the explosion characterized by the K _G (bar · m · s ^–1 ). These data are known for a small number of fuel gases in air and for a few unstable gases. The use of these P _max and K _G data will be developed in the article [SE 5 021] devoted to the prevention of gas explosions and the protection...