(40ap) Venting of Hydrogen Explosions

An established technique for preventing catastrophic failures of enclosures that may contain a flammable fuel-oxidizer mixture is to add explosion vents. These are structural elements that can vent hot gases from the enclosure, limiting the overpressure during the combustion event. In order to protect an enclosure against catastrophic failure, the explosion vents need to be sized appropriately so that they can vent the gases quickly enough while the enclosure pressure remains below acceptable thresholds.

Venting of fuel-oxidizer explosions involving hydrogen presents unique challenges due to its combustion properties. Hydrogen’s fundamental burning velocity of 312 cm/s is considerably higher than other fuel gases or vapors such as methane (40 cm/s) or even acetylene (162 cm/s). Burning velocity is an important parameter when sizing explosion vents. K_G, the deflagration index for gases, is the largest volume-normalized rate of pressure increase in a closed volume explosion and is sometimes used as a proxy for burning velocity in sizing explosion vents. The high burning velocity, and corresponding high K_g, of hydrogen can limit the effectiveness of explosion vents to mitigate hydrogen explosions.

NFPA 68 Explosion Protection By Deflagration Venting uses the burning velocity and the European Standard 14994 uses K_G to to calculate required vent areas. In this paper, we will compare these different approaches for sizing such devices, namely NFPA 68 and EN 14994 for several case studies. The paper will also address the potential of hydrogen-air mixtures to detonate.