EDUCATING BUILDING OWNERS ON THE MISCONCEPTIONS OF FIRE SAFETY IN RISER SHAFTS

January 30 2025

Alex Bardett, Managing Director of Ambar Kelly, underlines the importance of combating the common misconceptions around the use of non-combustible materials in riser shafts and the vital role that modular riser flooring can play in improving Higher Risk Building (HRB) fire safety.

What are the risks of using non-combustible materials in construction?

The recent Grenfell Tower inquiry revealed the chosen material can have a huge bearing on the spread of fire and smoke throughout any building, especially HRBs.

In fact, the tragic fire that day involved a combustible material being lit and then a fire rising in a void, forming a vertical shaft due to the lack of a horizontal fire break.

A previous fire at King’s Cross station in 1987 similarly involved a shaft ‘trench effect’. A discarded match lit a combustible material and then developed into a ‘flash over’, with the wooden escalators creating a ‘trench’ for the fire to rise up through.

How are upcoming changes to building regulations going to impact fire safety?

The Ministry of Housing, Communities, and Local Government (MHCLG) recently released a new parliamentary statement that will see changes to evacuation and fire safety provisions, including Approved Document B. When the project is complete or when the building is first occupied, fire safety information must be given to the relevant dutyholder.

In a move to support enhanced fire safety from 2^nd March 2025 onwards, the new updates will remove references to the national classification system for fire resistance, known as BS476. As such, Parts 6 and 7 will require construction products to be classified in accordance with EN13501-1, with performance classes A1 and A2 for non-combustible products and B, C, D, and E for combustible products.

Are non-combustible products actually more expensive as it is believed?

Many contractors see non-combustible steel plate materials, featuring pre-cut holes for M&E services that are covered by a lid, as being too expensive. While the initial outlay may be more, the cost won’t increase as the project progresses.

Conversely, the outlay for combustible GRP grating riser flooring will increase over time, due to post-installation works. For instance, GRP grating has to have holes cut into it to account for any services being fed through. To meet codes of practice and prevent the spread of fire during construction, temporary fire doors will need to be fitted. Indeed, grating, by its very nature, allows smoke and flame to pass through. This increases the overall project cost.

Are products that are labelled as having a fire rating still combustible?

Some suppliers will promote products that have a BS476 Part 6 & 7 fire rating, which is actually a measure of the spread of flame. GRP grating used as a riser flooring solution is often marked as such.

However, all GRP grating is combustible and will add fuel to any fire occurring in a riser shaft. The Grenfell Tower inquiry found this surface spread of flame test (BS476 Part 6 & 7) doesn’t measure combustibility. This is why it’s being withdrawn in March 2025.

If the designed riser flooring in an HRB is specified as non-combustible at Gateway 2, contractors may believe the GRP grating has the required ‘fire rating’ and attempt to hand the project over to ‘Gateway 3’. Despite it having a BS476 Part 6 or 7 declaration, it is combustible, meaning it will likely be rejected.

Are contractors responsible if products are changed mid-project?

A contractor may well be under the impression that the product’s supposed fire rating is correct, handing over the project to the next person in the chain.

There are often many occasions when a contractor will say ‘the sub-contractor has bought it and said it’s fire rated, so it’s not my problem.’ However, the situation isn’t always that straightforward.

Generally, the main contractor holds all the risk but won’t realise it. Furthermore, if a non-combustible class A1 steel riser flooring product is specified in Gateway 2 and replaced by a combustible Class C GRP product, it needs to be recorded in the change control plan so the impact of combustibility changes can be considered by the relevant teams.

Additionally, it must be documented before the Building Safety Regulator (BSR) signs off the building for handover at Gateway 3.

How can increasing knowledge and understanding improve fire safety?

Although Building Regulation changes will focus attention on fire testing and certification, helping suppliers and main contractors understand the benefits of non-combustible materials will go a long way towards improving fire safety in the built environment.

The Golden Thread enables anyone involved to have access to up-to-date information, ensuring a better understanding of the fire risks of using certain materials and the earlier identification of issues.

The government also needs to work with industry leaders to ensure regulations are met and quality standards adhered to.

Fire safety is essential in any building’s construction, so it’s imperative contractors are aware of the non-combustible opportunities, and benefits, available to them. They, and the end user, will benefit as a result.

How can suppliers help?

Just as important as contractors knowing their responsibilities if they change a specified non-combustible product for a cheaper combustible alternative, is the role of suppliers. Supplied products must be tested and certified to EN13501-1 to allow contractors and design teams to make an informed comparison between products.