Explosions can occur in vessels or enclosures containing flammable gases and/or dusts. Explosion venting, often referred to as deflagration venting (because we cannot practically vent detonations), is used to protect from catastrophic vessel/enclosure failure. Simplified equations are often used to determine the deflagration relief requirements. Simplified equations can be found in standards such as NFPA-68 . While easy to use, simplified equations tend to overestimate the relief requirements and have several practical limitations.
Simplified equations provided in NFPA-68  require the use of an explosion severity index, usually obtained from actual testing in a 20 liter sphere or a 1 m3 vessel. Published severity index data for flammable gases or dusts are also used. Typically, simplified equations for deflagration venting apply to ideal geometries and for short vent lines. They are not readily applicable to complex geometries, systems with elevated initial temperatures or pressures, hybrid systems containing flammable gases and dusts, systems with diluents and/or chemical oxidizers, systems with reduced venting set pressures, geometries with long L/D ratios or geometries with long vent piping where flame acceleration becomes significant.
We have developed detailed deflagration and explosion dynamics methods and computer codes that address many of the shortcomings of simplified sizing methods. These dynamic methods rely on a detailed representation of all possible independent combustion reaction(s) using direct Gibbs free energy minimization [2, 3, 4] coupled with a detailed burning rate model developed from measured explosion data using a 20 liter sphere or a 1 m3 vessel. We describe these methods in what follows and provide examples of how they are applied and how the burning rate models are developed from measured data.
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