Explosion within a helium purifier

Abstract

A cryogenic charcoal adsorber used to purify helium for cylinder filling exploded on August 26, 1988 at an Air Products facility in Belgium. Although the feed gas contained only 1.4% oxygen, calculations confirm that a liquid phase containing approximately 85% oxygen could have formed at the inlet to the bed and soaked into the charcoal. This potent explosive mixture (up to 7 times more powerful than TNT) was probably ignited by the flow surge when the bed depressurized to allow change-over from a full to an empty bank of cylinders. Parts of the vessel were recovered up to 250 meters from the installation and windows were cracked by the shock wave at approximately 60 meters. These consequences are consistent with the calculated energy available (approximately 40 lb TNT). Fortunately no one was injured. Two other recent explosions in the industry further emphasize the potential concerns of carbon bed cryogenic purifiers of oxygen containing gases.