Fire and Smoke Control
An essential part of fire safety in buildings is the avoidance of fire and smoke spreading through concealed spaces and gaps. The following guidance on how to achieve this is based on the Approved Document for Part B, Volume 2, applicable to flats and non-dwellings, covering England and Wales. Other national, regulatory guidelines have similar requirements.
Of course, the Building Regulations are only concerned with health and safety issues, so other measures may be appropriate to protect property, encouraged by insurers. They also only apply to buildings as completed - but the CDM Regulations 2007 place responsibilities on designers, contractors and clients to consider health and safety during construction, which could also justify extra measures. Finally, The Regulatory Reform (Fire Safety) Order 2005 imposes a general duty on the ‘responsible person’ to carry out a fire risk assessment of any existing non-domestic premises and act upon it, whether Building Regulations apply or not.
Returning to Part B, Section B3 (4) of the Regulations spells out a clear requirement that: ‘The building shall be designed and constructed so that the unseen spread of fire and smoke in concealed spaces in its structure and fabric is inhibited.’ Also, openings in fire-separating elements should be suitably protected to maintain continuity of fire separation.
Although these requirements may be met with other means, the simplest route is to use guidance provided in AD B. Two separate types of solution are defined in AD B:
• Cavity Barrier – A construction, other than a smoke curtain, provided to close a concealed space against penetration of smoke or flame, or provided to restrict the movement of smoke or flame within such space.
• Fire Stop – A seal provided to close an imperfection of fit or design tolerance between elements or components, to restrict the passage of fire and smoke.
CONCEALED SPACES
Concealed spaces and cavities offer an easy route for the spread of smoke and fire - and, being hidden, present an even greater danger than more obvious risks. To protect them, cavity barriers should be provided:
• to sub-divide ‘extensive cavities’ to give specified maximum distances between barriers (determined by the Class of surface/product exposed in the cavity)
• to close edges of cavities, including around openings
• to prevent fire spread to other properties from external walls
• generally to close junctions between cavity walls and compartment walls or floors
• to close some double-skinned insulated roof sheeting
• to continue protection above/below protecting walls of escape corridors and doors sub-dividing them
• to continue protection above/below bedroom partitions in institutional/other residential buildings.
The requirements for cavity barriers in floor voids is new. Unlike escape corridor and bedroom walls (discussed above), cavity barriers should not be used over compartment walls, which must themselves continue up to the compartment floor and be fire-stopped.
GAPS AND JOINTS
For fire separating elements (such as compartment walls/floors) to be effective, every joint, imperfection of fit or opening for services to pass through should be protected by fire stopping. This should also have the added benefit of reducing spread of smoke.
MEETING THE REQUIREMENTS
Fire stopping should have the same fire resistance (integrity) as the compartment or fire separating element it is protecting. But the situation for cavity barriers is less well-understood with AD B calling for a minimum of 30 minutes integrity and 15 minutes insulation. This requirement is not achievable with some systems – and often not enforced.
As with all the minimum provisions listed in Schedule A of the AD B, fire ratings are based on testing to the relevant part of BS476 or the equivalent European standard. Third part accredited (notably by UKAS) product conformity certification schemes are encouraged by AD B to demonstrate compliance. Specifiers should only use fire stop and cavity barrier products that satisfy all these requirements – such as the Lamatherm range – and demand appropriate evidence.
Fire stopping will require support or reinforcement by materials of limited combustibility where the unsupported span exceeds 100mm or where non-rigid materials are used without satisfactory test evidence. Wherever possible, cavity barriers should be tightly fitted to a rigid construction and mechanically fixed in position, then, if necessary, the junction should be fire stopped to ensure continuity. Lamatherm cavity barriers and fire stopping products are fully tested, complete systems incorporating the necessary supports and fixings.
AD B raises the issue of continuing effective performance of cavity barriers during a fire or in the event of movement due to building subsidence, shrinkage, temperature variations and wind pressure. Similarly, the ability of fire stopping at the head of compartment walls to accommodate deflections of as much as 40mm during fires is highlighted. Click here for more details about this essential consideration. [Link to article 3]. Lamatherm products are available using a unique, patented process of pre-compression to give an integral resilience capable of handling such movement and deflections.
Finally, AD B stipulates information that should be made available to the building owner/operator such as details or as-built drawings showing all passive fire safety measures including cavity barriers.
For full details of all Lamatherm cavity barrier, fire stopping and compartment floor upgrade systems, please see Fire Solutions.