Around 5:15 pm, a gas leak was noticed on an 11,750-litre capacity LPG tank being filled at a filling station. The delivery driver, assigned this operation, sounded the alarm. Fire-fighters sprinkled the tank to lower its interior pressure, installed a safety perimeter and evacuated the adjoining pharmacy, strip mall bar and nearby stores. Traffic was suspended in front of the station. An attempt to tighten the joint by a technician working for the tank owner failed. The decision was then made to transfer the LPG back to the tanker lorry that had performed the initial filling. Once this step had been completed, the cistern was flared.
This leak happened at the joint located between the LPG tank’s buffer and manhole flange. A pressure surge occurred within the cistern’s expansion space at the end of the filling step due to the scorching temperatures. The pressure, while less than that required to activate the relief valve, could not be withstood by the joint, which was a “new generation” part and made of fibreglass as a replacement of the previous asbestos models. The poor quality of clamping for this type of joint might have created conditions conducive for a leak.
In light of the extremely hot atmospheric conditions, gas delivery drivers were in fact advised to only fill cisterns to 80% of their capacity instead of 85%, with a pressure control setting of 14 bar instead of 16.
The Environmental Inspectorate requested the tank owner to explain why the joint had leaked before the relief valve, which was normally designed to eliminate the pressure surge (according to ESP regulations for pressurised equipment).
Once the joint had been changed the following week, new leaks were observed: on the relief valves undergoing permeability testing (6 bar) and on the manhole buffer/flange junction during filling (8.5 bar). The gas supply company decided to exchange the cistern on 21st July.
Additional investigations are underway on the small bulk cisterns of this same batch; these efforts involve periodic re-certification by means of sampling. The same model of relief valves, also inspected by sampling, is undergoing a thorough examination.
