A slight leak of boron trichloride (BCl3, a toxic and corrosive gas) occurred around 11:45 a.m. in a manufacturing workshop of an industrial gas plant. The gas detection alarms were triggered. Hydrolysis of the product, in contact with atmospheric humidity, generated white fumaroles, which in turn triggered fire detection on the premises. Following this second alarm, the operator preventively informed the emergency services and evacuated the 55 employees. The personnel secured the facility and plugged the leak. Firefighters came to the site but did not have to intervene. Employees return to their workstations at approximately 12:30 p.m.

The leak originated from a leak on the O-ring (pneurop type) at the outlet of the vacuum pump on the detoxification system’s connection hose. Excessive discharge pressure caused the hose’s seal to fail, as indicated by abnormal noise from the pump and significant variations in the pressure measurement. This increase in pressure was caused by accidental vaporisation (flash vaporisation) of residual BCl3 liquid in the pump’s feed line when a volume of “hot” gaseous BCl3 was degassed to the detoxification system.

The heat tracing of this line was out of order, which resulted in it cooling down and the subsequent liquefaction of the residual BCl3 gas. The line was not equipped with a second temperature sensor that would have detected the failure of its heat tracing system.

The operator replaced the line’s heat tracing system with a system with temperature protection and control. The temperature of each section is indicated on a display unit. The operator now includes the pump in the list of equipment subject to preventive maintenance.