At 10:45 a.m., an explosion occurred in a gutter covered by metal plates and used to run pipes under the workshop of a metal treatment plant. The explosion occurred when a screw on a furnace was being cut with an angle grinder. The employees heard and saw the explosion, which lifted the gutter’s cover plates. The operator cut off the workshop’s propane and methanol supplies, had the building evacuated, and notified the firefighters. They measured the gas concentration in the workshop but did not detect any danger of toxicity or other subsequent explosion.

It turned out that the propane pipe in the gutter was leaking in several places, particularly on a poorly tightened valve. The propane, which is heavier than air, built up in the gutter and exploded when it came into contact with the sparks from the angle grinder.

After the incident, the operator replaced the propane and water pipes in the gutter. It placed protections around the sections these pipes that run outside the gutter and installed a gas detector in the workshop. It established a procedure to annually check the gas pipes and test for gas in the air inside the workshop. It replaced the gutter’s cover plates with gratings or a cover with openings to limit the build-up of gas in the event of a leak. It recommended that its employees use a sabre saw rather than a grinder when occasionally cutting metal parts.