Compartment walls Cavity barriers

Main application in respect to this Design Guide:

• Maintaining the fire separation in roof spaces or floor voids where such voids run past compartment walls.

• Sub-dividing voids above ceilings or below floors or within walls to restrict unseen spread of fire (normally a regulatory requirement).

FUNCTION OF CAVITY BARRIERS

• To maintain the integrity of the barrier for the duration defined in Table 4.7 of the Design Guide. Cavity barriers installed between non-fire resisting elements to prevent rapid non-fire spread through voids, only require a 30 minute integrity as the elements to which they are attached will have failed before then. Restricting smoke spread is as important as maintaining integrity.

• To restrict the rise in temperature on the unexposed face to those levels required to prevent fire spread for the duration defined in Table 4.7 of the Design Guide.

• To restrict the passage of smoke for the same duration as integrity.

• To be not capable of spreading flame on their surface.

• To withstand the loading and deflection to be experienced in use and during fire exposure whilst maintaining the requirements above.

• To be able to accept the services described in Data sheet 6.7.1 without detriment to the fire separation provided, e.g. integrity, temperature rise and smoke restriction. To achieve the smoke restriction all penetrations shall be fully sealed.

• To maintain the separating performance over the life time of the building, or for a shorter duration if allowed for in the fire safety management plan, in respect of realistic impact and/or ambient conditions.

EVIDENCE OF FIRE PERFORMANCE

Evidence of performance shall comply with all of the following:

• Fire resistance performance (cavity barriers larger than 1m in any direction). The ability of the barrier to maintain integrity and keep the unexposed face temperature below hazardous levels shall be supported by test evidence generated in accordance with BS476: Part^1h, EN 1364-1²⁶ with edge fixings appropriate to its use and preferably supported by a Field of Application Report identifying any restrictions in use.

6 Design Guide for the Fire Protection of Buildings

• Fire resistance performance (cavity barriers less than 1m in any direction). The ability of the barrier to maintain integrity and keep the unexposed face temperature below hazardous levels shall be supported by test evidence generated to the test methodology given in BS476 : Part 20^1f, EN 1363-1²⁵ in a furnace with a minimum dimension of 1m. In such tests both vertical (or two opposite horizontal edges) shall be unrestrained. Barriers tested in this way shall be supported by a Field of Application Report identifying any restrictions in use.

• Smoke resistance. The barrier should have at least one impermeable face and the method of fixing shall be such that no gaps exist. Preferably the barrier shall have been tested to the methodology of BS476 : Part 31.1^1jand demonstrated a leakage rate of not more than 10m³/m²/hr.

• Contribution to fire growth. The surface of the cavity barrier, including any substrate, shall have a surface spread of flame of Class 1 to BS 476: Part 7^1d, and be rated Class 0 as defined in England and Wales Building Regulations, Approved Document B²⁹, or other national regulations. Alternatively the product shall be designated as being of limited combustibility.

• Loading and deflection. The method of installation of vertical barriers shall be able to accommodate vertical deflection of L/30 of its mean height, or span, without producing gaps through which smoke or fire could spread.

• Accommodation of services. Evidence shall be available to substantiate that the penetration by services will not impair the achievement of any of the above performance requirements.

• Durability. Evidence shall be available to show that the materials used in the construction of the barrier are not going to be adversely affected by the ambient conditions and, if appropriate, abuse (e.g. low energy impacts) during the anticipated life of the barrier.

The most common generic types of material used for fire resisting cavity barriers are as follows:

1. Calcium silicate and cement based boards 2. Unreinforced gypsum based boards 3. Reinforced gypsum boards

4. Mineral wool quilt

4.1 Mineral wool quilt (not less than 40mm thickness minimum density 60kg/m³)

4.2 Semi-rigid mineral wool slab (density 100kg/m³) not less than 25mm thickness

5. Steel faced fibre reinforced cement boards 6. Vermiculite sprayed mesh

7. Glass fibre based curtains

Construction design and data sheets 6

1. CALCIUM SILICATE AND CEMENT BASED BOARDS

There are a number of suitable products for use as cavity barriers. For large cavity barriers these take the form of a non-loadbearing partition with structural studs being used to support the boards and form joints. For small cavity barriers an appropriate sized board may be simply fixed to the boundary or edge members. Boards of less than 12mm thickness are not suitable for small, single sheet cavity barriers because of their lack of robustness.

FIRE PERFORMANCE DATA

• Fire resistance (integrity). Normally good, especially for low density boards with a low propensity to crack when heated. (✩✩✩✩✩)

• Temperature rise (insulation). Generally more conductive than some other barrier materials and may need to be used in conjunction with insulation to achieve ratings. (✩✩✩)

• Smoke resistance. Unless damaged they are considered impermeable although joints and edges may require special treatment. (✩✩✩✩✩)

• Contribution to fire growth. Normally Class 0 or limited combustibility and meet Part 2.2 of this Design Guide (✩✩✩✩✩).

• Loading and deflection. Only limited ability to withstand deflection and design details will need to be given to meet this requirement. (✩✩)

• Ability to accommodate services. Rigid enough to accept sealants around services and stiff enough to take pipe collars and penetration sealing systems. (✩✩✩✩)

• Durability. Generally considered inert although some are susceptible to water and subsequent freezing which should be used only in frost free areas. Low density products are prone to some impact damage. (✩✩✩) 2. UNREINFORCED GYPSUM BASED BOARDS

Generally as for calcium silicate boards except minimum thickness of single layer boards shall be 19mm.

FIRE PERFORMANCE DATA

• Fire resistance (integrity). Low propensity to crack but not totally immune; normally considered good. (✩✩✩✩)

• Temperature rise (insulation). Gypsum has excellent resistance to temperature rise until all water is driven off. (✩✩✩✩✩)

• Smoke resistance. Unless damaged, boards are considered to be impermeable, but joints and edge details will need to be developed to meet this requirement. (✩✩✩✩)

• Contribution to fire growth. Class 0 surface, core of limited combustibility. (✩✩✩✩✩)

• Loading and deflection. As for calcium silicate. (✩✩)

• Ability to accommodate services. Normally rigid enough to accept sealants around single services but support will be needed to retain special closing devices and sealing systems. (✩✩✩)

• Durability. Not suitable for use in wet conditions, but generally durable although prone to impact damage. (✩✩✩)

6 Design Guide for the Fire Protection of Buildings

3. REINFORCED GYPSUM BOARDS

Generally as for calcium silicate, except minimum thickness of single layer boards shall be 12mm.

FIRE PERFORMANCE DATA

The performance of reinforced gypsum boards is the same as unreinforced gypsum except for:

• Fire resistance (integrity). The material is unlikely to crack when heated and has excellent integrity performance. (✩✩✩✩✩)

• Ability to accommodate services. Stronger than unreinforced gypsum and some devices such as cable transits and pipe collars may be fixed directly to the board. (✩✩✩✩)

• Durability. More resistant to impact than normal gypsum board.

(✩✩✩✩)

4. MINERAL WOOL QUILT

The advantage of mineral wool barriers is their ability to be bent, curled or rolled for getting into small spaces when retro-fitted.

FIRE PERFORMANCE DATA