On January 25, 2005, an explosion at the Acetylene Services Company (ASCO) facility in Perth Amboy, New Jersey, killed three workers and injured a fourth. The three workers who died were shoveling snow near a utility shed when the shed exploded — a location they could not have known was accumulating explosive acetylene gas.

A valve design flaw in ASCO acetylene generator allowed acetylene to flow in reverse — backwards from the generator through water pipes and out of an open drain valve directly into the utility shed. A misaligned rubber plug enabled this reverse flow. Acetylene accumulated in the shed until it reached explosive concentration at the propane space heater used to keep the shed warm, igniting the gas.

The CSB found that the valve design flaw that allowed acetylene backflow was a latent defect that could have been addressed by the generator manufacturer through design improvement and user notification. The unsafe location of the pipe drain valve (which opened into the adjacent shed) and the absence of operational procedures preventing the water valve from being opened without water flowing were additional contributing factors.