Understanding Deflagration and Detonation Arresters

Ignition of flammable gas mixtures inside tanks, vessels, and vapor piping systems presents a significant hazard in industry. Many systems exist in multiple industries where this hazard presents itself, including tank vents to the atmosphere and vapor collection systems. If a flame front enters a vessel or piping system, then the resulting confinement will lead to a rapid rise in pressure as the flame propagates through the flammable mixture. In piping systems especially, the long aspect ratio, elbows, and other mechanisms induce turbulence that can accelerate the flame front to and above sonic velocity. The resulting detonation wave can generate even more damaging results. Given the nature of piping systems at chemical, oil, and gas processing facilities, an internal deflagration or detonation may spread throughout a facility impacting multiple vessels, systems, and workers leading to catastrophic fire and explosion consequences. The technology employed to arrest these flame fronts before they can enter or leave tanks and vessels or propagate through piping systems falls under the heading of deflagration (for subsonic flames) and detonation (for sonic/supersonic flames) arresters. Selection and application of the technology can be confusing and challenging to the design engineer. This presentation aims to provide an overview of the physics of a successful arrester and how to evaluate the process service to select an appropriate technology, and if necessary, how to test an arrester to confirm that it is fit for purpose. We will discuss the typical approaches to characterizing single gases and vapors along with vapor mixtures and the limitations provided by each type of technology.