Alert no. 437 | 01 November 2023 | Version 1

Hydrogen explosion and fire during the recommissioning of plant equipment post maintenance

What happened?

On 17 September 2023, at a chemical processing plant in North West Queensland, a release of pressurised hydrogen gas resulted in an explosion and fire injuring three workers and causing damage to plant. The incident occurred during the recommissioning of equipment after routine scheduled maintenance.

The injured workers included two workers who were completing the recommissioning and a store worker who was approximately 40 m from the location of the incident. The injured workers did not require hospitalisation; however, the event had the potential to cause a more significant adverse effect.

How did it happen?

Investigations are ongoing and the information in this publication is what is known at the time of writing.

The safety alert aims to draw attention to the occurrence of a serious incident, raise awareness of risks, and prompt assessment of existing controls.

Based on available information, several contributing factors have been identified, including:

• the failure of a butterfly valve, under hydrogen header-pressure of approximately 2000kPa, is the direct cause of the incident.
• the bearing bush bolts of the butterfly valve may not have been correctly installed at the time of overhaul resulting in separation of valve bearing bush.

Key issues

• High pressure valves must be quality checked for correct assembly post maintenance overhauls.
• Effective systems and processes that ensure quality assurance must be used for the overhaul and testing of the valves to prevent failure of such valves.
• The maintenance of the equipment involved in hydrogen usage must comply with Original Equipment Manufacturer (OEM) specifications.

Recommendations

All Site Senior Executives (SSEs) should:

• Remember that hydrogen is considerably more hazardous than liquid petroleum gas (LPG), as it possesses a wider explosives range, and the ignition energy is approximately 13 times lower than that of the LPG. Further, the low viscosity and small size of a hydrogen molecule create the potential for gradual dispersion through the atomic matrix of solid metal, such as pipework, leading to additional challenges in containing hydrogen.
• Employ highly sensitive and specialised detection method, as detecting hydrogen gas leaks can present difficulties, particularly due to its tendency to disperse rapidly.
• Refer to OEM specifications to ensure work methods and testing procedures are suitable for application, when working on a hydrogen equipment.
• Ensure suitable trained personnel are engaged in maintenance and quality assurance.