Compartmentation

Floors should normally be tested or assessed in accordance with local regulations such as BS 476: Part 21: 1987 in the UK and are required to satisfy the three failure criteria of loadbearing capacity, integrity and insulation when exposed to fire from below.

Loadbearing concrete floors supported by steel beams and protected with a suspended ceiling should be tested or assessed to BS 476: Part 23: 1987 or a local equivalent.

The following points should be considered when determining the correct specification to ensure a timber floor will provide the required fire performance:

The key area for consideration is that there are no gaps left at the junction between the wall, any structural member and the external cladding, that will result in compartmentation to be breached and allow the passage of fire.

The same level of fire resistance at the junction should be provided as the level for the compartment wall.

Consideration must be made to possible gaps forming because of deformation of any structural element and/or the external cladding.

If a fire breaks out near the area where a compartment wall meets a roof, there is a risk that it will spread over the roof to the adjoining compartment. To reduce the risk, Building Regulations (Document B) requires protection to be installed to a protected zone of the roof 1500mm either side of the compartment wall. However, for more onerous circumstances, the FPA Design Guide suggests a minimum of 2500mm, or up to 5000mm dependent upon the orientation of the ridge and the presence of a sprinkler system

The FPA Design Guide is a document aimed at protecting businesses against disruption and loss of critical stock and machinery due to fire. Within the document there is information on extent of the zone, fire ratings expected by insurers and the industry as a whole.

Depending upon its situation and function within a building, a wall may need to fulfil different requirements in the event of fire. Fire resisting walls used for partitioning buildings and enclosing compartments will be required to provide a barrier to the passage of fire from one side or the other or both sides. The wall must therefore be able to satisfy each of the relevant criteria (integrity, insulation and if the wall is load bearing - load bearing capacity) from either side for the prescribed period.

Factors for consideration when determining the correct specification to ensure a wall or partition will provide the required fire performance include:

• Nature and thickness of facings
• Studwork and fixings
• Compartmentation at head of wall
• Deflection
• Partition length
• Load bearing
• Cavity insulation
• Service penetrations
• Light switches and electrical sockets
• Fire doors and glazing
• Protected zones
• Concealed spaces

Chapter 5 of the Fire Protection Handbook provides examples of system specifications for a range of applications and required fire protection periods. Additional system details are available in the Technical Data Sheets.

The proximity of a building to the relevant (facing) boundary determines the probability of it being a danger to other buildings on adjoining sites or of it being  at risk from a neighbouring building on fire. Regulations such as Building Regulations (Document B) in the UK specify different fire resistance periods for external walls depending upon their distance from the relevant boundary.

Where the walls are required to provide fire resistance only from the inside, loadbearing capacity and integrity are required to be satisfied for the full period; whereas insulation is often a shorter time. 

Satisfactory constructions will be very different from those required to maintain insulation for the full period and where fire resistance is required from either side.

The following points should be considered when determining the correct specification to ensure an external wall will provide the required fire performance:

• Distance from the relevant boundary
• External cladding
• Structural steel
• Single storey buildings
• Cavity barriers
• Thermal insulation
• Impact resistance
• Wind loading

Chapter 5 of the Fire Protection Handbook provides examples of system specifications for a range of applications and required fire protection periods. Additional system details are available in the Technical Data Sheets.

Local building codes provide guidance on where such barriers should be located within hidden voids in a building and they give examples of deemed-to-satisfy barriers for voids in stud walls or partitions.

If a barrier in a concealed space coincides with a compartment wall or floor it will normally be required to provide the same fire performance as the wall or floor. If the barrier is located between such walls or floors however, the barrier is defined as a ‘cavity barrier’ and as such will normally only be required to provide 30 minutes integrity and 15 minutes insulation. There are also instances where insurance companies insist on 30 minutes insulation.

Factors for consideration when determining the correct specification to ensure a smoke barrier will provide the required fire performance include:

• Size of barrier and location
• Differential movement
• Service penetrations
• Adjoining structures

Chapter 9 of the Fire Protection Handbook provides examples of system specifications for a range of smoke barriers.

• PROMAFOUR^® System: ideal for building a false chimney breast for a cassette/inset type fire place. A safe reliable, robust chimney breast insulation system, developed to resist continuous high temperatures of up to 1000°C. 

• PROMAFOUR^® Boards: a non-combustible board which can withstand a maximum continuous operating temperature of 1000^oC. Ideal for use as a lining behind a wood burning stove or heating appliance.

• SUPALUX^®: a non-combustible board which can withstand a maximum continuous operating temperature of 80°C. Ideal for use behind a wood burning stove or heating appliance.

Heating appliances come in many formats and Promat strongly recommends that the heating appliance manufacturer and the flue or chimney manufacturers be consulted to ensure that the correct installation procedures are followed. Temperatures in excess of 80°C can have a severe effect on the overall structure where the heating appliance is mounted.

The area around a wood burning stove, for example, can reach up to 400°C which far exceeds the 45°C maximum recommended for plasterboard.

The main functions the board provides are:

• Providing a flat, heat resisting lining to an existing hearth
• Reflecting the majority of heat back into the room
• Providing a thermal barrier capable of withstanding up to 1000ºC continuous working temperature, with a material which is inherently non-combustible

In the UK, the requirements for the installation of heating appliances in buildings are covered by the Building Regulations in Approved Document J - Combustion appliances and Fuel Storage systems.

Within this document, Requirement J2 deals with the protection of building, and states that "Combustion appliances and fluepipes shall be so installed, and fireplaces and chimneys be so constructed and installed, as to reduce to a reasonable level the risk of people suffering burns or the building catching fire in consequence of their use."

Particular care is required to ensure that hot radiating surfaces are kept clear of combustible materials such as timber. Minimum distances are prescribed, and the use of non-combustible lining materials is indicated, and the guidance given must be followed at all times.

Please note that Promat have not performed any tests which allow the minimum distances from combustible material specified in Approved Document J to be reduced.