Explosion Hazards of Gas and Vapor Mixtures

Premixed flame laminar and turbulent burning velocities are two parameters that are sometimes needed to evaluate explosion hazards.  There is ample information in the literature regarding the burning velocities of most common ignitable gases and vapors in air.  These values have been obtained through a range of experimental techniques over the years.  Little information, however, is available regarding the combustion characteristics of gas mixtures.

Flammable gas mixtures occur in many chemical processes.  Current guidance regarding hazard analysis of combustible gas blends involves using the characteristics of the most hazardous of the fuels in the blend to determine explosion hazards.  This approach, however, may be overly conservative in cases where the most hazardous fuel species represents a small percentage of the blend.  There is a need to calculate the explosion hazard characteristics of a blend of fuels.  This requires the use of a global parameter of the mixture, which can be used to quantify its explosion hazard.

This study explores the role of the premixed laminar burning velocity as a global parameter to measure the explosion hazard of a mixture in a vented enclosure or vessel.  The relationship between laminar burning velocity and maximum vented explosion overpressure (based on correlations developed in the NFPA 68 Standard on Explosion Protection by Deflagration Venting technical committee) is described.  The laminar burning velocity is shown to be a critical factor in determining the severity of a potential vented explosion. 

Several correlations for the laminar burning velocities of fuel mixtures will be explored and compared with available experimental data.  A relatively simple Le Chatelier-type mixing rule is shown to provide a good estimate of the burning velocity values for a range of fuel mixtures.  This calculation can, in turn, be used to compare the vented and unconfined explosion hazard of a fuel blend to known fuels.