At a biogas production facility, a break of sealant occurred at 1:15 am near a gas meter. This sealant loss stemmed from a release of biogas at the gas meter location due to an imbalance between incoming and outgoing flow rates. Once the maximum gas meter capacity had been reached, biogas escaped via the facility’s hydraulic safety valve. This phenomenon may be anticipated by monitoring the level. On the day of the accident, a physical defect (connection problem) at the end of a valve stroke neutralised the automated mechanism controlling the operational set-up, thereby blocking the possibilities to transfer or flare the biogas, which when not extracted from the gas meter was subsequently degassed.

Incapable of acting remotely, the facility operator travelled to the site in order to manually activate the set of valves on the transfer network, in an effort to rectify the situation. Since one of the valves was “hard” to operate, several minutes of repair time working with a self-breathing apparatus were necessary. The situation returned to “normal” 25 minutes later; 600 kg of biogas had been released (composition: 65% methane, 34% CO2, with impurities including H2S at 50 ppm). No adverse consequences were observed outside the facility.

This incident revealed the vulnerability of devices at the end of an operating cycle. The operator decided to modify system design to increase reliability and extend the detection range. These “hard” valves were replaced to simplify manual handling should the need arise.