IOGP high potential event report

Incident description:

An operator located near the oily water pit was alerted, by a personal gas detector alarm, to the presence of hydrocarbon gas. The operator went towards the oily water pit, and the personal gas detector indicated a 100% LEL flammable atmosphere at 150mm from the oily water pit. The operator established, through a process of elimination, that the source of gas was the oily water drain line from the V1 suction scrubber on screw compressor 3 and he proceeded to shut down the unit and inform his line supervision. The leak rate has been estimated, through process calculation, to be 88.6kg/h. The total volume of gas to atmosphere is currently unknown. The previous operator check undertaken at 19:40 hrs on the 21/07/2018 did not indicate any abnormalities. Therefore, the initiating event likely occurred between these two operator visits which were approximately 19 hours apart. Worst case scenario is that 1683 kg of gas was released to the atmosphere. No one was hurt, and no community members were affected by the incident. This incident was classified has a Tier 2 Process Safety Event.

What Went Wrong:

Mechanical Instrument Failure Concurrent failure of the compressor scrubber level controller and the low level safeguard resulted in a flow path to the oily water drain, which is vented to atmosphere.

Corrective Actions:

Lessons Learned: 1) Risk normalisation: The oily water pit was perceived to be a safe release point. 2) Learning from Incidents: An identical gas blow by incident occurred two months prior. 3) Safeguarding: Inadequate (1) proof testing procedure and (2) actual proof testing execution. Recommendations: 1) Re-engineer the scrubber low level safeguarding function to reduce the likelihood of dangerous unrevealed failures. 2) Develop specific proof test procedures for the scrubber low level safeguarding function, and execute them as per CMMS schedule. 3)Implement previously identified H&RA controls. Establish a hard barrier exclusion zone around the oily water pit. Draft Investigation report and LFI complete, with Operations manager (investigation sponsor) for review.