Removal of an isolation was identified as one of the causes of the Piper Alpha disaster. The operators did this to start a pump without realising its relief valve had been removed for maintenance. The underlying cause was that the pump isolation was not cross referenced with the removal of the relief valve.
This paper summarises several issues with process isolations based on the events at Piper Alpha, namely use of shared isolations and management of change. Process isolation is a critical and complex subject, and this paper only touches on the subject. A key message is that people can often perceive an isolation as guaranteeing safety when the reality is that it is only a means of reducing rather than eliminating a risk.

Published in Loss Prevention Bulletin June 2018