Key learnings from a high potential incident
HPI OSH Alert #470
Date of incident: 26 November 2015
Safety Flash issued: 01 December 2015
A mechanical fitter and trades assistant were removing a failed gearbox from a wedge gate valve at a pump station to enable repair work to be carried out.
While removing the valve gearbox retaining nut, the valve stem and wedge gate assembly fell into the valve body.
This resulted in a pressurised flow of waste water escaping which carried the retaining nut, gland packing and a certain amount of floatable debris from the valve body.
The waste water drenched the workers and the retaining nut narrowly missed hitting them before landing at the back of the work platform.
Why did this happen?
Beyond the basic cause (being the removal of the nut from unsupported valve stem), the causes of the incident are summarised as follows:
- Design failure – the valve is a cross over valve, a single point of failure which cannot be isolated while maintaining station operations. The design should have taken account of the need to carry out such maintenance activities.
- Non-standard valve design does not have retaining collar – unknown deviation from expected industry standard (based on local knowledge and experience).
- Personnel reliance on own knowledge and experience as opposed to referring to support documentation (internal/external information).
- Inadequate Work Instructions – Inaccuracies within records combined with team and management structural changes.
- Inadequate hand over process to ensure continuity in job planning.
- No warning signs/documentation informing of consequences of removing the locking/thrust nut.
What will the business area involved in the incident do to stop this from happening again?
- Conduct a prioritised desktop audit of all remaining regional wide affected valves, supported by targeted field inspection to identify valve makes, types, sizes, drives.
- Embed process to deal with non-standard work to include reference to all relevant manufacturer's operating and maintenance manuals and other literature.
- Develop and embed a documented handover process for extended periods of employee absence/s.
- Fit appropriate warning labels to any identified gearbox drive valves.
What will our organisation do to stop this from happening again?
- Review design of the system and the need for a second valve to enable isolations and station operations to be performed concurrently.
- Investigate improvement opportunities for information storage and electronic document field retrieval system(s) and physical tags for assets (i.e. bar code, QR code or RFID system).
What key learnings can you discuss with your team to stop this from happening again?
Appropriate job planning is essential to all works we undertake
- How long do you or your team spend planning the tasks that you will be undertaking?
- How do you or your team identify non-standard assets and then adequately plan for the tasks?
- What steps do you or your team take when there is proposed change in job planning? How frequently do you share day to day lessons learnt including identification of non-standard assets with your team?
- How do you think the job planning process could be improved within your teams?
If you would like further information about anything included in this HPI OSH Alert, please contact Charis Neumann, Snr OSH Analyst – Incidents, (08) 6330 6629.