FIRE SAFETY


Fire safety issues when designing ‘green’ buildings


Speaking in a topical session at the IHEEM Wales Regional Conference in Cardiff on 11 May (see also HEJ – August 2023), Anthony Pitcher, Senior Fire Safety Adviser, NHS Wales Shared Services Partnership – Specialist Estates Services (NWSSP – SES), discussed some of the key fire safety challenges when seeking to decarbonise healthcare buildings – for instance those arising from large-scale use of timber as a ‘standout feature’ in building structures, and around the combustion risks from electrical vehicle charging points.


Anthony Pitcher began his presentation – titled, ‘Principles being adopted and challenges to be considered for fire safety and the decarbonisation agenda’ – by admitting that the decarbonisation agenda had ‘caused much recent head-scratching’ among fire safety professionals; currently, there were ‘more questions than answers’. Starting by focusing on embodied carbon, he showed a slide of the ‘Construction Materials Pyramid for Embodied Carbon’ – ‘an interactive online tool for comparing the global warming potential of various construction materials’ (Figure 1). He said: “You can see that the materials towards the top of the pyramid (such as steel, concrete, and bricks) are very good from a fire safety perspective, but pretty damning from a global warming one, whereas those at the bottom (such as straw, and wood-based products) are great from a carbon perspective, but all pose a fire safety challenge; they burn nicely.” He next showed a CGI of the atrium


(Figure 2) at the new Velindre Cancer Centre in South Wales – which the architects, White Arkitekter, and the project sponsors, Kajima, / Sacyr / ABDN and ‘projectco’, ACORN, say is ‘set to become the UK’s greenest hospital’. “You can see that the atrium is a pretty


impressive pretty space, with the primary structural materials being mass timber CLT and glulam beams,” Anthony Pitcher explained.


Char insulates the inner core While impressed with the aesthetics of the predominantly timber-structured atrium, the speaker said that, ‘from a fire safety perspective, we all know that timber burns, so we have a bit of an issue there.” He told delegates: “In fact timber is a pretty unique material – when it burns, it effectively protects itself, forming a char which insulates the core.” Char factors were, he explained, predictable, depending on the type of wood, the species, and the moisture content. “Typically,” he explained,


Figure 1: The Construction Materials Pyramid for Embodied Carbon.


“we’ll be looking at char factors of around 1-1.5 in / hour, so wood can really be considered a unique material.” Looking at the various relevant design


codes, Anthony Pitcher said that while these assumed uniform char factors with ‘normal timber’, mass timber didn’t necessarily burn the same way, and can be subject to a process of delamination. He explained: “What happens is that exposed wood burns, chars, and the char can then fall off, exposing more clean wood behind. You thus get into a process of ‘cyclic burning’.” Key factors to impact on cyclic burning included the number of layers and the composition of the wood, as well as the types of fire-rated adhesive. The speaker added: “There is another approach you can use to protect the timber – encapsulation, where you encapsulate the mass timber in plasterboard.” He continued: “I’m sure you’ll all agree that the atrium at Velindre wouldn’t look half as impressive if it was just a boarded plasterboard structure, concealing the natural beauty of the wood – so that form of protection kind of defeats the aesthetic objective.” One of the key considerations with timber – and particularly mass timber – Anthony Pitcher said – is that it is ‘a


bespoke product’. He elaborated: “It is unique to the individual supplier, so we can’t mix and match. This presents some challenges in fire safety testing which – post-Grenfell – have become even more stringent.”


Joints and penetrations Turning to some of the other fire safety ‘implications’ around mass timber, Anthony Pitcher said: “We must really focus on the detail in the joints and penetrations. Weak joints can potentially risk the integrity of the compartmentation. When we look at the various materials and tests, there’s a scarcity of tested details for penetration seals, particularly for CLT.” Acknowledging that the industry was ‘improving in this area’, he cautioned: “I’ve yet, however, to see a tested detail of a fire damper being installed directly into a CLT form of construction.” Turning to ‘building geometry’, the


speaker said: “Here we’re looking at large spans and deep beams. We recently reviewed a scheme which utilised CLT and glulam beams, with 24 metre timber spans.” The scale and the size of the timber had been ‘incredible’. He explained: “The columns were about 2.5 feet square, and the beams six feet deep.”


September 2023 Health Estate Journal 37


Image © Centre for Industrialised Architecture (CINARK) from Royal Danish Academy.


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