In the evening, 2 security guards conducting rounds were in the process of inspecting a storage building in a chemical plant containing raw materials and finished products when their measuring instrument sounded. The instrument indicated a concentration of 50 ppm of carbon monoxide (CO). Arriving on the scene at 9:50 p.m., the firefighters, wearing breathing apparatus, began to look for the source of the CO.

The installation director and the site’s security manager activated the internal contingency plan at 10:30 p.m.

At around 11:15 p.m., a high concentration of hydrogen (2,000 ppm) was located in a room where forklift batteries were being charged. It is normal for hydrogen to be released when batteries are being charged. However, the gas had accumulated in the room as it had been closed for 3 days. This hydrogen concentration had interfered with the CO detection instruments.

One of the roundsmen, suffering from headaches and nausea, was taken to hospital for a check-up. The internal contingency plan was cancelled at 11:18 a.m.

Analyses showed that the battery being charged was not faulty. An older battery, as was the case here, releases more hydrogen than a newer battery when it was charged, but the quantities remain well below the limits. The problem, in this case, was that a small amount of hydrogen makes the CO detectors react disproportionately. However, a new battery was ordered to replace the battery responsible for the incident.

The ventilation and hydrogen detection system (3 probes) was checked and determined to be in compliance. The operator has pointed out that a possible area for improvement would be to equip the facility with a portable hydrogen detector to make accurate assessments in such situations.