Operator enters toxic cloud as failed shear coupling triggers ammonia leak and sensor misses detection—safety systems and response under review

A recent ammonia leak at a Western Australian manufacturing site has brought renewed attention to emergency release systems and operator response protocols after a shear coupling failed during a routine loading operation—triggering a toxic release that could have resulted in serious harm.

What Happened

In August 2024, a serious incident occurred during the loading of liquefied ammonia into a rail tank wagon. A shear coupling on the loading arm failed in an unsafe manner: two out of three bolts broke, jamming the coupling open and allowing compressed ammonia to escape. The failure led to a significant loss of containment (LOC), forming a dense ammonia vapour cloud.

To compound matters, a proximity sensor intended to detect the coupling failure did not activate. The ammonia leak continued until gas detection sensors eventually triggered a Safety Instrumented System (SIS) shutdown of the ammonia supply.

The first operator on scene further increased personal risk by entering the vapour cloud without respiratory protection, unaware of the severity of the failure.

Shear Couplings and Their Safety Role

Shear couplings, also known as emergency release couplings, are designed to protect workers and facilities by acting as a mechanical failsafe. In the event of excessive force—such as unexpected movement during loading—they are meant to break cleanly and automatically seal both ends of the pipeline to prevent hazardous leaks.

These systems are common in high-risk environments including:

• Marine terminals for fuel and liquefied gas exports
• Road and rail tanker gantries
• LNG and LPG distribution to power utilities and mine sites

The coupling involved in this case was expected to ‘fail-safe’ but instead failed in a manner that negated the functionality of both the proximity sensor and the mechanical shut-off mechanism.

What Went Wrong

The investigation uncovered a number of underlying issues:

• History of prior failures: Previous post-loading bolt failures had not prompted any formal review of coupling integrity.
• Ignored structural concerns: Flexure issues with the loading arm had been raised but the equipment remained in service.
• Operator assumptions: The operator assumed a minor release was occurring and failed to wear self-contained breathing apparatus (SCBA).

Corrective Actions and Industry Learnings

Following the incident, the site operator introduced a series of corrective measures:

• Adoption of an upgraded emergency release coupling design
• Inclusion of the coupling in the site's preventative maintenance program
• Enhanced training with a focus on learning objectives and repeated response drills

Industry-wide, the incident has prompted several takeaways:

• Design scrutiny: Ensure that emergency coupling mechanisms genuinely offer the level of risk reduction required. OEM designs vary and should be reviewed for suitability.
• Failure mode analysis: Any critical control—like a shear coupling—must be assessed to ensure its failure cannot bypass detection systems or safety interlocks.
• Response preparedness: Workers may respond to major events using routines suited to minor incidents. This ‘normalisation of risk’ increases hazard exposure.

The report urges operators to embed intuitive response protocols, such as:

• Protect yourself first
• Communicate for help
• Assess whether to seek refuge
• Use appropriate PPE, including SCBA where necessary
• Follow incident response principles aligned with training

A Preventable Near Miss

While no injuries were reported, the ammonia release incident serves as a sobering reminder of how safety-critical equipment and human factors can intersect to create risk. Ensuring mechanical integrity, functional fail-safes, and a culture of vigilant, trained response are essential in any environment handling dangerous goods.

For further information, safety guidance is available via the WA Department of Energy, Mines, Industry Regulation and Safety, including codes of practice for hazardous chemicals, risk assessment, and plant safety.