5 . 2
ALTERNATIVE FIRE ENGINEERING APPROACHES AND QDR
Within Approved Document B, it is acknowledged that alternative routes to compliance may be necessary for cases falling outside of its scope, ie uncommon building situations. For those cases, it is said that the functional requirements B1 to B5 may be satisfied via alternative methods or evidence. Herein, these are generally referred to as alternative fire engineering approaches, which could involve one of three possible methods as defined in BS 7974:
Where an alternative fire engineering approach is considered necessary/appropriate to meet the project goals and demonstrate compliance with the Building Regulations 2010, it is expected that any such solution will be developed following the guidance in BS 7974. This will include the completion of a qualitative design review (QDR) in consultation with all relevant stakeholders. BS 7974 provides a structured process for highlighting and determining fire hazards, fire risks, design actions and mitigation measures and will typically involve the following main stages:
– Quantitative methods. – Probabilistic methods. – Qualitative methods.
– Review architectural design and selection of materials, including their suitability and fire properties, occupant
characteristics and client requirements. – Establish functional objectives for fire.
The most appropriate route to compliance for any project (including commercial buildings with mass timber structures) should be discussed and agreed at the inception stage. For small buildings, adopting design guidance (often referred to as a prescriptive-based approach) may be suitable. However, for taller buildings and thus with higher failure consequences in the event of fire, an alternative fire engineering approach is likely to be required.
– Identify fire hazards and possible consequences. – Establish trial fire safety engineering designs. – Set acceptance criteria for the designs. – Identify the method of analysis. – Where identified, establish fire scenarios for analysis. – Document outputs of the QDR. The QDR for each project can be different depending on project specifics, complexity, goals and challenges of the building in question; accordingly, the level of detail of the QDR may vary between projects.
SUPPORT IN THE CHOICE OF COMPLIANCE ROUTE
Acknowledging the uncertainty in the relationship between mass timber and conventional routes to fire safety compliance using Approved Documents, the Structural Timber Association (STA) have published the structural timber buildings fire safety in use guidance, Volume 6 9 . This document intends to clarify the appropriate route to compliance for a mass timber structure in function of its height and use, with emphasis on Regulation B3(1) which concerns structural stability in the event of fire. The
Figure: Hybrid timber structure in construction
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