OSH alert - Main sewer coring work, potential hazardous gas event (July 2016)

Key learnings from a High Potential Incident.

Hazardous Substances incident iconHPI OSH Alert #484

Date of incident: 29 July 2016

Safety Flash issued: 10/08/2016


What happened? Image of sewer connection incorrectly sealed

On 30 July, complaints were received from members of the public regarding wastewater odour issues. Operations crews were dispatched and identified that an access chamber on the Main Sewer line had been cored, with a pipeline inserted to enable a connection to a new odour management unit.

The connection point was not adequately sealed, causing odours to the surrounding area. While coring into the side of the access chamber, appropriate controls were not put in place to ensure
adequate protection from potential hazardous gases (i.e. Hydrogen Sulfide - H2S) from the main sewer.

Why did this happen?

  • Project management procedures were not followed to ensure appropriate controls and supervision of
    high risk activities.

What will the business area involved in the incident do to stop this from happening again?

  • Re-assess competency of all relevant operational Clearance to Work (CTW) authorised persons.
  • Develop and implement a management reporting system for project hold points (i.e. project risk assessment, construction risk assessment etc.) enabling management oversight.
  • Review Principal contractor and subcontractors capability to deliver remaining works in progress
  • Review the contractor engagement process to identify opportunities for improvement around prequalification, bid assessment and Verification of Competency for high risk works.

What will our organisation do to stop this from happening again?

  • Develop a network-wide gas monitoring program for main sewers to better understand the risks associated with hazardous gas levels in a closed sewer system.
  • Conduct a risk review to determine how to proceed with existing asset security. Develop a 1–3 year plan to build in-house capability for odour management.
  • Review current process and controls for opening main sewer and pressure main discharge access chamber covers.
  • Identify opportunities to improve current CTW process, including additional entry permit to cover opening main sewer and assignment of specific competency.


What key learnings can you discuss with your team to stop this from happening again?

High Risk Work construction activities must have adequate levels of risk mitigation measures in place

  • How do we ensure adequate levels of supervision and competency for any High Risk Work activities?
  • What is the current process for our teams to ensure safe job planning documents are reviewed and feedback is given?
  • Have we developed and implemented a formal process to ensure safe job pre-planning and a coordinated approach to the planned work occurs?

When multiple parties are involved in planned work, it is crucial to have a clear understanding of all roles, responsibilities and activities across the entire job.

  • When would a Clearance to Work be required?
  • What is the role of the Contract Manager and Authorised Person in the Clearance to Work process?
  • If a job changes, what do we need to do or who do we need to contact, to make sure we continue working safely?
  • How does our team discuss our planned work and the potential risks of the activity?

Main sewers and pressure main discharge access chambers may have elevated levels of hazardous gases (and operate under pressure) that can pose hazards to the surrounding environment.

  • Be aware that we can have very high concentrations of H2S in our wells and pipes. Water Corporation have measured concentrations higher than 1200ppm within our sewer systems.
  • The health effects of hydrogen sulphide (H2S) depend on how much H2S a worker breathes and for how long. However, many effects are seen even at low concentrations. Effects range from mild, headaches or eye irritation, to very serious, unconsciousness and death.
  • What are some of the controls required to be in place before accessing a main sewer access chamber?

Further information

If you would like further information about anything included in this HPI OSH Alert, please contact Charis Neumann, Senior OSH Analyst Incidents, (08) 6330 6629.