Explosion in Microbiological Anaerobic Chamber -

The Microbiological Anaerobic Chamber of approximately 2 m3 capacity was containing an explosive mixture of hydrogen and air. A fire followed the explosion, but was rapidly extinguished by staff using fire extinguishers, prior to the arrival of fire service personnel. The pressure wave from the explosion damaged neighbouring building and an injury.

The local operating procedures used in the lab allowed high concentrations of hydrogen to be introduced into the chamber. A worker inadvertently admitted air to the chamber whilst undertaking maintenance, allowing the hydrogen enriched atmosphere in the chamber to mix with air, and subsequently ignite, most probably on contact with the oxidation catalyst in the chamber, resulting in the explosion and subsequent fire.

The INITIATING cause is related to a human error: a worker inadvertently admitted air to the chamber while doing maintenance, allowing the hydrogen-enriched atmosphere in the chamber to mix with air and subsequently ignite, most likely on contact with the oxidation catalyst in the chamber, resulting in the explosion and fire.

Microbiological Anaerobic Chamber

An unknown concentration of hydrogen was present in the chamber, presenting a significant fire and explosion risk. The incident occurred during maintenance.

DESCRIPTION OF THE PROCESS
Mixtures of inert gases and hydrogen are intended to be routinely used in the type of anaerobic chamber involved in the incident. The mixtures used in the chamber involved were produced locally in the laboratory using nitrogen, carbon dioxide, and hydrogen. 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.

The pressure wave from the explosion blew windows out of the laboratory, with glass hitting a passer-by on a path outside, and glass shards landing up to 30 m away. Ceiling panels were dislodged in the laboratory and adjacent rooms, and a worker using the apparatus at the time was taken to hospital by ambulance to have burns treated. They have subsequently fully recovered from their injuries. Another worker in the lab at the time required medical observation but was otherwise unharmed.

From H2TOOLS Lesson Learned: "The practice of making gas mixtures in the laboratory should be eliminated, and gas mixtures with a known low hydrogen concentration should be purchased for use. The concentration of hydrogen used should be such that it is not possible to form an explosive mixture on dilution with air. "