A leak occurred during the replacement of one of the two cylinders of silane in an electronic components factory. A technician from a subcontracting company was repressurising the distribution circuit after changing the cylinder when the silane was released. The leak on a pneumatic control valve caused a small flame to appear for a few seconds. The fixed detection system (gas and flame) caused the installation’s safety valves to close. The technician present also activated the emergency stop mechanism (same effects as the fixed detection system).

The failure of the pneumatic valve caused the silane to enter the “valve operating chamber”, and then be released into the atmosphere. The discharge then continued despite the unit being secured and the pipe upstream of the faulty valve remaining pressurised. Silane concentrations of up to 40 ppm were detected 1 m from the leak.

The operator set up a 30 m safety perimeter, evacuated the neighbouring workshop and alerted the fire service. Upon their arrival, the emergency services evacuated the factory, extended the perimeter to 100 m around the establishment then vented the residual gas from the installations under the protection of CO2 extinguishing equipment. No one was injured.

Several measures have been implemented: replacement of the second pneumatic valve of the same type, integration of the annual replacement of these valves into the maintenance schedule, and a feasibility study for the performance of leak testing before repressurising the silane circuit when changing cylinders.