Concerning misconceptions of fire safety in riser shafts

1 Educating building owners of riser shaft fire safety needs to happen now
2 Fire resistance V non-combustible
3 Change control plan and material changes
4 The chimney effect
5 Golden Thread
6 Moving forward
7 Related articles on Designing Buildings

[edit] Educating building owners of riser shaft fire safety needs to happen now

The Grenfell Tower inquiry has substantially changed the fire safety landscape in the UK, placing fire performance and material specification under intense scrutiny – especially in high-risk buildings (HRBs). As a vertical void linking all floors of a building which, if not protected, can become a fast lane for the spread of smoke and flame, the riser shaft is a hugely important but often overlooked area. Widespread misconceptions about riser shafts and the materials used to build them continue to expose projects to avoidable risks and underline why the industry needs to address this blind spot.

During the construction process, riser shafts can function as open chimneys. If poorly specified or left unprotected, they offer a direct route for smoke and fire to rise unchecked. This risk was tragically demonstrated in the Grenfell Tower fire and echoed in the King’s Cross Underground fire of 1987, where super heating of the combustible material in the wooden escalator led to a ‘shaft effect’ and deadly flashover.

[edit] Fire resistance V non-combustible

Despite legislative changes and a sharper focus on fire safety – especially in HRBs – many in the construction industry still confuse ‘fire resistance’ with ‘non-combustible’. This misunderstanding can often lead to the specification and use of inappropriate or outdated materials, particularly in the riser shaft.

The need for better understanding of the risks of fire in HRBs and the necessity of using non-combustible materials is exacerbated by data from the Home Office’s online Incident Recording System (IRS), which revealed there were 707 fires in high-rise buildings in England in the year ending September 2023 – a 17% decrease compared to a decade ago. While this drop is encouraging, the data highlights the risk fires still present, especially in HRBs, and why stricter regulation and better understanding is crucial.

[edit] Change control plan and material changes

Changes to Approved Document B and the Building Safety Act represent a much-needed shift. From March 2025, BS476 Parts 6 & 7, long used to measure surface spread of flame, were formally withdrawn and replaced by the EN13501-1 standard, which clearly classifies materials by combustibility. Only Euroclass A1 and A2 products will qualify as non-combustible. Conversely, the commonly used glass-reinforced plastic (GRP) grating, meanwhile, is Euroclass B to E and therefore combustible.

However, the problem remains that many suppliers still promote GRP based on its old BS476 Part 6 & 7 classification – creating a false sense of compliance. If these materials are substituted post-specification and not recorded In the Change Control Plan, a project could fail Gateway Three approval by the Building Safety Regulator (BSR).

A major issue lies in the assumption that product choice is solely the subcontractor’s responsibility. In fact, as riser flooring is a permanent works rather than a temporary protection, it should therefore be specified by the designer. Under CDM 2015 and the Building Safety Act, all duty holders, including contractors, architects, and quantity surveyors, are accountable.

If a non-combustible A1 riser flooring product is swapped for a combustible GRP option, this should be considered an unacceptable alternative. Furthermore, if that change isn’t recorded and assessed, the risk may fall squarely on the principal contractor, whether they realise it or not.

[edit] The chimney effect

This is further complicated by a major testing gap. There is currently no fire test specifically for a complete riser shaft. Individual elements are tested in isolation, but the combined ‘chimney effect’ – a key factor – is not accounted for. In real fires, materials interact differently when vertically installed in shafts, accelerating flame spread in ways isolated tests cannot predict.

It is widely assumed that steel plate non-combustible solutions are too expensive. While the upfront cost may be higher than GRP, total lifecycle costs often tell a different tale. In fact, combustible alternatives typically require multiple post-installation interventions. For instance, cutting service penetrations into GRP grating on site increases risk and labour costs. Temporary fire doors may also need to be fitted on every floor to prevent smoke and fire movement through the shaft during construction. These ‘hidden’ extras, combined with slower installation times, drive up overall cost.

[edit] Golden Thread

The introduction of the ‘Golden Thread’, a live, digital record of fire-critical information, is a major step forward. For it to be the most effective, those involved in specifying, procuring, and installing riser shaft systems must be better educated on the difference between fire-resistance and non-combustible.

Designers must therefore move away from referencing withdrawn standards, while contractors must be more rigorous in documenting substitutions, and suppliers must stop promoting outdated performance claims.

[edit] Moving forward

This is supported by the fact that one of the biggest challenges fire consultants face is cultural, rather than technical. In fact, people still assume that if something passes any fire test, it must therefore be suitable. This is simply not the case. Consequently, sharing knowledge and raising awareness across the entire supply chain is just as important as the technical solutions themselves.

While the number of fires in high-rise buildings is lower than it was a decade ago, this isn’t the time for complacency. Every fire is a test of a building’s systems, the built environment’s understanding, and the industry’s will to improve.

The legacy of Grenfell Tower must be a commitment to prioritise safety over convenience, and performance over price. Especially in HRBs, where the consequences of poor specification are most severe, the construction industry must insist on certified and tested non-combustible solutions. And must document them rigorously.

Quite simply, there is no room for ambiguity. The built environment must now align on clarity, compliance, and above all, responsibility.

AT Journal Issue 156 Winter 2025. "Educating building owners on the misconceptions of fire safety in riser shafts needs to happen now" written by Alex Bardett, Managing Director, Ambar Kelly.

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