Summary of incident
In August 2024, while loading ammonia into a rail tank wagon at a manufacturing site, a shear coupling on the loadout arm failed to an unsafe mode. Two out of three bolts failed and wedged the coupling open, which resulted in a loss of containment (LOC) of compressed liquefied ammonia that formed an ammonia vapour cloud.
A proximity sensor adjacent to the shear coupling was not actuated. Consequently, release of the toxic gas continued until gas detection activated a safety instrumented system (SIS) shutdown of the ammonia supply.
As the first responder, the operator escalated their risk by entering the rapidly forming toxic vapour cloud without respiratory protection, increasing their exposure potential to an acutely hazardous atmosphere.