The Weekly Reflektion 01/2022

Research and Development can lead to new understanding that can change the way safety systems are designed and operated. One example is the release of water deluge in the event of agas leak.

Deluge Release on Process Facility

How do you keep yourself updated with research and development related to the safety of your facilities?

In the Reflektion from week 46 in 2021 we used an incident from 1987 that caused a serious hydrocarbon leak on an installation in the North Sea. The production operator that discovered the leak initiated the water deluge manually as he escaped from the process module. We said that we would return to this decision in a later Reflektion.

Automatic release of the deluge on a confirmed fire detection was and is normal practice on offshore installations. Automatic release of the deluge in a hydrocarbon leak (unignited) was not part of the logic in the emergency shutdown system on this installation. At the time of the incident there was disagreement in the industry on the benefits of releasing a seawater deluge in the event of a hydrocarbon leak. Some operators believed that a deluge release could reduce the consequences of an ignition by reducing explosion overpressures and reducing the hydrocarbon available for combustion. Other operators were concerned that release of a deluge could provide an ignition source either by static electricity from the deluge nozzles or by causing faults in electrical equipment. 

In the early 1990s the Christian Michelsen Institute in Bergen, Norway was commissioned by the UK Department of Energy to investigate the potential beneficial effects of deluge water sprays on the overpressures generated by gas explosions. The tests showed that overpressures in gas explosions can be significantly reduced if the water deluge is initiated before the ignition. However, there were two competing mechanisms. In compartments with poor ventilation the deluge could cause increased flame acceleration and therefore higher overpressures. In better ventilated compartments the evaporation of the water droplets interfered with the reaction between the hydrocarbon and oxygen and reduced the overpressures, even stopping the reaction completely in some cases. The Petroleum Safety Authority (PSA) in their regulations state. ‘The systems shall be automatically activated by a signal from the fire detection system. In the event of gas detection, the systems shall be automatically activated if this can lead to lower explosion pressure.’ PSA require therefore that analyses and tests are carried out to determine the effect of the deluge and from this knowledge a decision is made on the automatic release of a deluge on detection of gas. 

Tests were also carried out in the 1990s that showed that release of a deluge with seawater could not generate an ignition source from static electricity as the seawater conducted away any charge built up at the nozzles.

The production operator that released the deluge was asked why he took the action. He answered that it seemed the right thing to do in the circumstances. In the absence of better knowledge and understanding then the people in your organisation will do what they think is best. Do you ensure that their best is in fact the best that could be done?