Exposure to residual hydrocarbons when breaking containment

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Alert ID: 
Description of Process: 

A work party were involved in the replacement of a flushed and purged section of 3” hydrocarbon pipework, including a 1” bypass section


Description of Incident: 
  • Hydrocarbon pipework had been isolated and flushed. The 3” section, connected to the 1” bypass section via a take-off, was changed out successfully.

    As the final cut was made to the horizontal section of the 1” bypass, a release of a small amount of trapped residue/vapour occurred.

    The following morning, personnel presented to the medic due to exposure to hydrocarbon vapours.

    Investigation findings:

    Examination of the removed 1” bypass revealed a solid partial blockage which may have contributed to the trapping and release of residue/vapour.

    As the preparatory pipework flush appeared to have been successful, the possibility of a blockage and trapped residue/vapour had not been recognised nor mitigated against.

    Despite exposure to released vapours, the work party personnel continued working for a few moments to complete the task.

Good Practice Guidance: 

•Preparation of plant for intrusive maintenance must consider system complexity and the potential for trapped hydrocarbons and deadlegs.

•Ensure development of detailed task risk assessments and adoption of appropriate control measures to mitigate against the potential for trapped hydrocarbons and deadlegs.

•Personnel to be fully aware of emergency response actions, fully discussing and agreeing upon these during toolbox talks.


Related Step Change resources:

Guidance – Hydrocarbon Release Reduction Toolkit https://www.stepchangeinsafety.net/safety-resources/publications/hydrocarbon-release-reduction-toolkit


Safety moment – Deadlegs: not just a hazard in football https://www.stepchangeinsafety.net/safer-conversations/safety-alerts/safety-moment-deadlegs-not-just-hazard-football


Joined-up Thinking – Communication https://www.stepchangeinsafety.net/safety-resources/joined-up-thinking/joined-up-thinking-resources/communication-high-res-video

Causes and consequences of incident or accident: 
Release of a harmful substance
Uncontrolled release of a flammable gas or liquid
Contributing factor: 
Control of work


There was a lack of flanges/valves available in the section of pipework.

A key part missed in the breaking of containment prior to conducting the work was a benzene check on the broken spool section. Had this been conducted, the HC would have been identified and the job stopped immediately for further investigation.