Forty-six hydrogen cylinders were accidentally charged with air instead of additional hydrogen during recharging operations at a synthetic liquid fuels laboratory. Cylinders were manifolded in batches of 10 or 12 to the utility compressor outside the laboratory. In normal operations, partly used cylinders containing hydrogen at a pressure of 800-900 psi were recharged to a pressure of 2000-2100 psi. Since the contaminated cylinders contained a highly explosive mixture of about 40% hydrogen and 60% air, it was decided to release the compressed gas to the atmosphere outside the building after grounding the cylinders. Two of the cylinders were successfully discharged, but an explosion occurred while the third cylinder was being discharged. Two chemical engineers were killed by the blast, an operator was injured and required hospitalization, and the laboratory building and equipment were damaged.
The investigating committee postulated that 1) there may have been oil present in the regulator that ignited at a relatively low temperature and then ignited the hydrogen-air mixture, or 2) there may have been a metallic compound present that catalyzed the oxidation and subsequent ignition of the hydrogen-air mixture. Other possible causes that were considered less likely were 1) the existence of a leak around the attachment of the regulator to the cylinder, with ignition of the leaking gas by friction or static spark, and 2) ignition of the cylinder contents as a result of the electrical potential of a fire alarm post against which the cylinder was leaning while being discharged.
The probable cause for the contamination of the hydrogen cylinders was that the 3-inch gate valve on the hydrogen intake line to the compressor was closed during the filling operation. It was not possible to determine with certainty how the air entered the system due to conflicting testimony of laboratory employees. However, it likely entered through one or more of the many valves on the compressor suction system, any one of which may have been inadvertently left open.
- Hydrogen Storage Equipment
- Gas cylinder
Several recommendations were outlined by the investigating committee to govern future operations of the hydrogen compressor in the synthetic liquid fuels laboratory:
Install a cutoff that will shut down the compressor when the suction pressure drops to a positive pressure of one to two inches of water.
Install an oxygen analyzer with an alarm as close to the compressor suction inlet as possible.
Attach all cylinders to the filling rack, discharge the contents to the atmosphere, and evacuate before filling.
Analyze as soon as possible the contents of at least one cylinder of each rack of cylinders charged.
Eliminate the recycle connection from the suction side of the compressor to the blowdown pot.
When compressing hydrogen, disconnect all interconnecting lines from the hydrogen suction line except the inert gas line.
Establish more definite procedures and responsibilities for maintenance repairs, construction, and operations.