Design benefits of automatic sprinkler systems granted under approved document B

This article was originally published as part of The impact of automatic sprinklers on building design, an independent report produced by WSP, sponsored by the Business Sprinkler Alliance (BSA), published in September 2017.

Introduction

Approved Document – B (ADB) has been approved and issued by the Secretary of State for the purpose of providing practical guidance with respect to the fire safety requirements of Schedule 1 and Regulation 7 of the Building Regulations 2010 for England and Wales.

ADB recommends automatic sprinklers for most building types with a storey above 30m high. A notable exception to this rule is hotels which do not require automatic sprinklers regardless of height.

The sections below detail how automatic sprinklers can affect building design.

Building layout / means of escape

ADB offers limited concessions when automatic sprinklers are incorporated, but the following options can create some flexibility in the building layout as detailed below:

Multi-storey flats with a floor above 4.5m are recommended to have the following unless automatic sprinklers are provided:

• An alternative exit should be provided from each habitable room that is not on the entrance floor of the flat;
• One alternative exit from each floor should be provided, with a protected landing that is entered directly from all habitable rooms on that floor;
• Additional smoke alarms in all habitable rooms.

When an automatic sprinkler system is provided in residential care homes, ADB permits the following:

• Fire doors to bedrooms need not be fitted with self-closing devices;
• Protected areas may contain more than ten beds;
• Bedrooms may contain more than one bed.

Compartmentation and fire protection

Fire severity, building height and its occupancy all have an effect on the necessary fire resistance. The provision of automatic sprinklers can reduce the required fire resistance as highlighted in blue in Table 4-1.

Table 4-1 shows that due to the installation of automatic sprinklers, an office not more than 18 m tall can reduce its fire resistance from 60 minutes to 30 minutes and an office not more than 30 m tall can reduce its fire resistance from 90 minutes to 60 minutes. In certain tall buildings, more than 30m high, automatic sprinklers are required regardless and in small buildings no concessions are offered.

Raised storage areas which are frequently erected in industrial and storage buildings are not subject to the minimum periods of fire resistance displayed in Table 4-1 if they meet certain conditions including limits on the area of the floor, no more than 100m2. This limit can be removed if automatic sprinklers are installed.

[Table 4-1 ADB recommended minimum periods of fire resistance (reductions with sprinkler provision are highlighted in green)]

Compartments should be limited in size according to the height of a building and its intended use. Automatic sprinklers either remove limits on compartment sizes, or increase them in the following situations:

• Single-storey shops: 2,000 m2 to no limit
• Multi-storey assembly, recreational and commercial building: 2,000 m2 to 4,000 m2
• Multi-storey industrial building not more than 18 m: 7,000 m2 to 14,000 m2
• Multi-storey industrial buildings more than 18 m: 2,000 m2 to 4,000 m2
• Single-storey storage building not more than 18 m: 20,000 m2 to no limit
• Single-storey storage building more than 18 m: Not permitted to no limit
• Multi-storey storage building not more than 18 m: 20,000 m3 to 40,000 m3 (compartment volume)
• Multi-storey storage building more than 18 m: 4,000 m3 to 8,000 m3 (compartment volume)

Access to buildings for fire-fighting personnel

Buildings must be designed so that fire-fighting personnel have access without delay and with a sufficient operating base which allows effective action to be taken. The installation of automatic sprinklers allows the number of firefighting shafts and fire mains to be reduced:

• If the building is not fitted with sprinklers, then sufficient firefighting shafts should be provided such that every part of every qualifying story is no more than 45 m from a fire main outlet in a protected stairway.
• If the building is fitted with sprinklers, then sufficient firefighting shafts should be provided such that every part of every qualifying story is no more than 60 m from a fire main outlet in a firefighting shaft.

Smoke extraction and venting can benefit firefighters in performing their duties whilst also benefiting those evacuating a building. This is enhanced in basements where there is less opportunity for the heat and smoke to be vented outside via the windows as would happen above ground. Accordingly standard guidance recommends that sufficient ventilation is provided for large basement areas (larger than 200m2). This can be achieved via openable natural vents but this can be difficult to achieve on a congested site due to the large vent discharge area required at ground floor. Alternatively automatic sprinklers can be used in tandem with a mechanical ventilation system. This has the advantage of requiring a smaller vent discharge area reducing the impact the chosen solution has on the building layout at ground level [3].

External fire spread / fire-rated facades

To prevent fire spread between buildings ADB recommends that a portion of the building’s façade should be fire-resistant or adjacent buildings be sufficiently separated. The amount of the façade required to be fire-rated is proportional to the distance between the façade and the site boundary. Automatic sprinklers are recognised as a significant inhibitor of fire size and therefore fire spread. ADB accordingly states that radiation from a sprinklered building on fire can be assumed to be halved and allows the separation distances required between buildings to be halved or the proportion of the façade that can be unprotected / non-fireresistant to be doubled.

[Figure 4-1 Defining non-fire-rated/unprotected façade area.]

References

• [3] In this scenario, it is not considered necessary to install sprinklers on the storeys other than the basement unless they are needed for other reasons.

--Business Sprinkler Alliance 10:07, 03 Oct 2017 (BST)

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