Outdoor exposure risks and arson protection

5.6.1 GENERAL CONSIDERATIONS

Where premises are identified as being at risk to an arson attack or from an accidental fire occurring in outdoor storage or processes it is especially important that:

• suitably designed standards of security and fire safety management are established at the design stage to reduce the potential threat;

• these standards are clearly defined before any decision is taken regarding the fire resistance of the external envelope of the building;

and

• consideration is given to the siting of buildings and outdoor storage or processes in relation to each other and to the site boundary.

Note: In practical terms, the method referred to in 5.4.1 for determining boundary distances does not take into account the storage of combustible materials between the building and the boundary and, therefore, the boundary distance thus determined may not adequately deal with this risk.

This approach should enable a more cost effective approach to be taken to the whole question of protection against these types of fire.

Notes: 1. Buildings which otherwise comply with the provisions of this Design Guide may be compromised if insufficient consideration is given during the risk assessment process to the potential for an arson attack on or malicious ignition in the building. In addition, the risk of fire spreading and involving buildings on the site as a result of accidental ignition occurring in outdoor storage or processes must be considered.

2. The provision of an ‘apron’ or clear area around the building designed or furnished with features to deter the storage of goods or materials can be an effective prevention of fire spread.

3. It is essential that good standards of security and fire safety management are established and maintained. Guidance on these aspects should be sought from insurers.

5.6.2 RECOMMENDED PROTECTION AGAINST MALICIOUS IGNITION

This section of the Design Guide gives guidance on the additional fire resistance which should be considered to ensure adequate property protection is provided against the risk of fires which are started deliberately.

Remove hazard or improve security or specify fire-resisting external walls

Figure 5.6. External exposure from arson attack (see 5.5).

5 Design Guide for the Fire Protection of Buildings

The introduction and maintenance of good standards of housekeeping and fire safety management is essential in all premises and will help to reduce the impact of a fire started maliciously. In support of such standards, however, it is essential that the relevant standards of fire protection detailed in this Design Guide are applied to all buildings, whether or not a risk of malicious ignition exists. These standards should be increased as detailed below where an un-acceptable risk is identified.

5.6.2.1 Passive fire protection

The materials used in the construction of the external walls and roof of the building(s) should conform to 2.2 and 5.5.3 respectively of this Design Guide in order to control and minimise the growth and spread of a fire. In many premises this will give adequate protection, including those potentially at risk to arson attack, providing good standards of fire safety management and security are practised.

However on premises where combustible materials, for example, wood pallets, waste bins, stock and the like, cannot be kept a safe distance from the buildings, the following additional protection should be considered:

(1) The sections of the external walls and roof which are at risk from nearby combustible materials should have a fire resistance of not less than 30min integrity and 15min insulation.

(2) Where it is important to protect high values or critical business equipment or processes, consideration should be given to increasing the levels in (1) above to 60min fire resistance as regards both integrity and insulation.

(3) It is equally important that windows and doors have similar levels of resistance as regards integrity or that they are not put at risk by storage etc.

(4) The length of the protected zone on either side of the compartment wall may need to be extended to prevent fire in external storage compromising the separation provided.

Hazardous plant or combustible storage Refer to 5.6

Boundary distance

Building

Figure 5.7. Outdoor exposure or arson risk.

External fire exposure 5

(5) The provision of soffits and barge boards, including any proposed ventilators, which will resist the passage of fire for a suitable period. The following recommendations should be considered:

• provision of soffits and barge boards of materials conforming to 2.2;

• the guidance given in 3.4.4 (d) of this Design Guide concerning the siting of ventilators; and

• the provision of effective cavity barriers where walls, whether or not compartment walls, are bypassed by the soffit box.

5.6.2.2 Sprinkler protection

The provision of automatic sprinkler protection in buildings can be taken into account when deciding the level of fire protection required to overcome the threat posed by external storage.

It is, however, especially important that the effectiveness of the sprinkler installation is not impaired as a result of a large number of sprinkler heads operating simultaneously following the failure of a large section of the external wall or roof.

The guidance on sprinkler protection given in 5.4 and 5.5 should be followed and it should be noted that there will be occasions when it will be advisable for the external walls and/or roof to be of fire-resisting materials even though the building is sprinkler protected.

Figure 5.8. Extension of protected zone to reduce risk of fire spread from arson attack on combustible materials stored in yard (plan).

Boundary

Yard storage

Protected zone Compartment

wall

Arson attack Extended protected zone to comply with 5.6.2.1

5 Design Guide for the Fire Protection of Buildings

5.6.3 EXPOSURE TO FIRE FROM EXTERNAL ACCIDENTAL SOURCES

The site layout of all premises should take account of the threats presented not only on the premises but also from adjacent premises. As regards the premises in question the comments made in other parts of this section are equally applicable to the prevention of fire spread from accidental fires. The creation of ‘fire breaks’, that is, clear areas, between buildings and storage or to protect against fire spread from adjacent sites can be very effective.

Figure 5.9. Outdoor exposure and arson risk -plan view (see 5.6).

Hazardous plant or storage

No extensions or outdoor storage in this area unless guidance in Part 5 is complied with

Minimum 10m clear space

Different occupancy

Woodland

Distance should be adequate for exposing risk

Separating distance must be adequate

Acceptable positions for potential building extensions Yard

Yard Yard

Yard

Road

Surrounding property may present potential threats to the fire safety of the premises but with well considered planning at an early stage the risks imposed can be eliminated or at least controlled or reduced to acceptable levels capable of protection.

To combat threats to the buildings posed by accidental external sources of fire the designer may therefore wish to consider specifying an external cladding system having fire resistance and insulation as specified in 5.4.2.1. However as previously stated it is preferred that adequate provision be made to prevent storage of combustible materials nearer than 10m from the building and at suitable distance from surrounding property or boundary fences or walls.

5.7 Reference

BRE report: External fire spread: building separation and boundary distances, Fire Research Station, 1991