The H2Incidents database contains three incidents in which excess hydrogen was unintentionally introduced into an anaerobic chamber in a laboratory setting. The combination of hydrogen, air, and an ignition source proved to be extremely hazardous; two of the incidents resulted in explosions, and the third came very close to an explosion. The incidents were all caused by human error, which highlights the importance of 1) proper training and 2) not becoming complacent when working with hydrogen. Just because you think you have an anaerobic system environment, it doesn't mean that air or oxygen will be far away, and special care must be taken at all times.

Anaerobic chambers are often used in biochemistry laboratories for research that requires an oxygen-free environment. To achieve that state, nitrogen is first used to purge most of the air out of the chamber. Then a small amount of hydrogen is introduced into the chamber to scavenge the last remaining traces of oxygen. Often laboratories request cylinders containing a mixture of 95% nitrogen and 5% hydrogen for this purpose, which could be considered a best practice. Pure hydrogen should not be used due to the potential for an explosive mixture to form if any air were to inadvertently be introduced into the chamber. Two of the incidents described below resulted in explosions; a third situation was caught in time and an explosion was narrowly avoided.

Key lesson learned: Verify the contents of all gas cylinders to make sure that the vendor did not make an error and supply the wrong composition.

Hydrogen Explosion in University Biochemistry Laboratory

A hydrogen explosion in a university biochemistry laboratory resulted in four persons being taken to the hospital for injuries, all of the exterior windows being blown out, and significant damage within the laboratory. The explosion occurred when pure hydrogen, rather than nitrogen, was mistakenly introduced into an anaerobic chamber as part of the initial purge. Normally, three nitrogen purges are performed first, and the remaining small amount of oxygen is removed by reaction with hydrogen in the presence of a catalyst to form water. Because of the error, the hydrogen concentration reached an explosive level inside the chamber due to the relatively high concentration of oxygen. Ignition was probably caused by either an electrical source inside the chamber or the hot catalyst. This incident highlights the need for constant vigilance when working with hydrogen.

Hydrogen Explosion in Microbiological Anaerobic Chamber

An explosion and fire occurred in an anaerobic chamber containing a mixture of hydrogen and air. The pressure wave from the explosion blew windows out of the laboratory, with glass hitting a passerby outside the building and glass shards landing up to 30 meters away. One worker was taken to the hospital with burns. Mixtures of inert gases (nitrogen and carbon dioxide) and hydrogen, which are routinely used in the chamber, were produced in the laboratory. The hydrogen in the mixture reacts with any oxygen present in the chamber, on a heated catalyst, to eliminate oxygen and keep the chamber anaerobic. A worker inadvertently admitted air to the chamber while doing maintenance, thus allowing the hydrogen-enriched atmosphere to mix with air. Ignition was probably caused by the hot oxidation catalyst in the chamber. This incident highlights the need to follow standard operating procedures even for laboratory maintenance activities.

Incorrect Flammable Gas Cylinder Attached to Anaerobic Chamber

A research technician entered a laboratory to begin preparing samples that were to ultimately be purged in an anaerobic chamber. The technician looked at the chamber to see if it was adequately inflated and noted that the meter indicated that the hydrogen concentration was at 43%, well above the LFL. An alarm light was flashing on the meter, but an audible alarm was not heard. The technician checked the labels on the compressed gas cylinders hooked up to the chamber and discovered that one of them was a mixture of 95% hydrogen and 5% nitrogen, instead of the 5% hydrogen and 95% nitrogen that the research staff had requested. The vendor clearly failed to supply the customer with the requested mixture, but the customer should have verified the cylinder contents before the cylinder was used in the lab. This type of a mistake, with inverted percentages of the two gases, might be difficult for a technician to catch if they are simply looking to see "95%" and "5%" on the cylinder label. But since the consequences of such a mistake could be catastrophic, the laboratory should institute a standard operating procedure to ensure that the contents of every cylinder are verified and the person doing the verification has signed off on some type of mandatory form.