Risk of gas explosion - Prevention and protection

There are two ways of controlling the risk of gas explosions in confined spaces: preventing gas explosions and protecting installations against the effects of explosions.

Preventing gas explosions is based on controlling the composition of gas phases outside their flammable range, and on eliminating ignition sources, as required by ATEX regulations.

Preventing gas explosions is an essential step in process development, which can be tackled quickly because the necessary information can be easily gathered. Preventive methods include avoiding flammable gas phases by design, inerting enclosures with an inert gas such as nitrogen, lowering the temperature of liquid phases below their flash point, lowering the concentration of volatile fuels below their combined LEL, and phlegmatizing unstable gases or vapors by adding an inert gas. The identification and elimination of ignition sources is the subject of European ATEX regulations, the essential requirements of which are described below. Constructive measures based on lessons learned from the past can help avoid tragic mistakes. Finally, a number of techniques for avoiding air back-diffusion and its consequences in installations normally maintained under inert conditions are recalled.

The protection of enclosures against the effects of gas deflagration relies on the installation of explosion vents to reduce the explosion overpressure to a value compatible with their mechanical strength. Techniques for calculating these vents based on the characteristics of gas explosions P _max and K _G were developed very early on in Germany and German-speaking Switzerland by Bartknecht and adopted in the USA by the NFPA. Then these methods evolved in the USA through NFPA's use of increasingly elaborate correlations aimed at avoiding the need to measure the deflagration characteristics of gases, but at the same time, neglecting their peculiarities. All the stages in this process are described in this article, so that everyone can understand how the equipment currently in use is protected. Of particular interest is the information on high initial pressures. The protection of pipelines containing flammable gas mixtures is discussed. The protection of industrial installations by explosion suppressors and rapid isolation systems is also described.