Fire Performance of M&E Fixings in Mass Timber Buildings

A major UK research project has found that the fire performance of M&E fixings in timber buildings can be significantly improved through relatively simple changes to fixing specification. As mass timber construction continues to grow, the sector is increasingly seeking to anticipate potential challenges and address them through research, testing and collaboration.

Commissioned by the Fire Service Research & Training Trust (FSRTT) and supported by the Alliance for Sustainable Building Products (ASBP), the study investigated how fixings used to support services such as ventilation systems, pipework, electrical installations and fire suppression systems perform when exposed to fire.

The research, led by Professor James Glockling, Principal Fire Protection Engineer at BMT and Chair of a BSI standards committee on ‘Hazards to Life from Fire’, examined fixing failure mechanisms and identified practical solutions that can help ensure critical building services remain supported for longer during fire, reducing risks to occupants evacuating a building and firefighters undertaking emergency intervention.

One of the study’s most significant findings was that longer, slimmer hardened-steel fixings were shown to maintain retention for longer by reducing heat transfer into the timber and ensuring that critical thread engagement remains within unaffected material.

Past research

Earlier research undertaken by Dr. Dale Kinnersley of the Fire Protection Association found that the load-bearing capacity of fixings attaching sprinkler pipes to timber ceilings could be lost relatively quickly under fire conditions, potentially on timescales that could impact occupant and fire service safety.

The study was informed in part by lessons from the Shirley Towers fire in Southampton, where two firefighters tragically lost their lives in 2010. The incident occurred in a reinforced concrete residential building and prompted significant changes to guidance on the use of surface-mounted plastic cable trunking and plastic cable clips after investigations highlighted the dangers that can arise when electrical services become detached and create entanglement hazards for firefighters operating in smoke-filled conditions.

In mass timber buildings, the scenario is different but related. Whereas the Shirley Towers event involved the premature failure of weak plastic fixings attached to a non-combustible concrete structure, this study focused on how the performance of steel fixings can be affected by changes within a timber substrate exposed to fire.

Key findings

Using a purpose-built fire test rig, the project examined how factors including fixing diameter, embedment depth, loading, thread design and material type influence performance under realistic fire conditions.

In contrast to the longer, slimmer hardened-steel fixings, the research found that larger-diameter fixings, while often stronger under normal conditions, can lose load-bearing capability more rapidly during fire exposure. This occurs because larger fixings conduct heat more effectively into the surrounding timber, reducing its strength around the fixing threads.

Importantly, the research concludes that the issue can be addressed through relatively simple design measures, including selecting appropriate fixing types, ensuring sufficient embedment depth and understanding how heat affects the timber substrate during fire.

The findings are expected to contribute to future discussions on standards development, industry guidance, fire engineering practice and fire service training.

Dr James Glockling said:

“Good fire safety engineering is often about identifying issues before they become problems. This research has improved our understanding of how fixing systems behave under fire conditions and demonstrated that relatively simple changes to specification can make a significant difference to performance. The findings provide an important evidence base for future guidance, standards and industry practice, helping to address a significant but previously under-explored fire safety issue.”

Related work

The project forms part of a wider programme of work led by ASBP and its partners to address some of the key technical and insurance-related barriers to the wider adoption of mass timber construction. This includes the highly successful Mass Timber Insurance Playbook, which received endorsement from the Association of British Insurers and generated significant international interest, leading to the publication of a US edition.

Ongoing projects include guidance on assessing and repairing damaged mass timber buildings, practical guidance on managing water and moisture risk, and further fire safety research investigating the role of sprinkler systems in mass timber buildings.

Simon Corbey, Executive Director at ASBP, said:

“The findings are both important and encouraging. The research demonstrates that fixing performance under fire conditions can vary significantly depending on specification, but it also shows that practical solutions are already available. This is exactly the kind of proactive research that helps ensure guidance, standards and industry practice evolve alongside the growing use of mass timber construction.”

The study, Preventing Firefighter and Evacuee Entanglement, Electrocution and Obstruction Risks in Timber Buildings on Fire, was funded by the Fire Service Research & Training Trust and supported by RISCAuthority, with materials and technical support provided by KLH and Midfix.