Office buildings have specific fire safety requirements under BS 9999 and Approved Document B. Here's what a fire strategy for an office building covers.
3 September 20244 min readFire Safety Services
Office Buildings and Fire Safety
Office buildings have specific fire safety characteristics that distinguish them from residential and retail occupancies. The occupants are typically familiar with the building and its escape routes, are alert and mobile during the day, and are present in relatively predictable numbers. These characteristics allow office fire safety strategies to take a more straightforward approach to evacuation than residential or healthcare buildings, but they introduce different challenges in terms of compartmentation, fire load management, and the increasingly complex fit-out arrangements that modern office buildings require.
Applicable Standards
The primary standard for fire strategies in office buildings is BS 9999:2017 — Fire Safety in the Design, Management and Use of Buildings. BS 9999 provides a risk-based framework that allows fire safety provisions to be tailored to the specific characteristics of the building and its occupancy, rather than applying prescriptive rules uniformly. This makes it particularly well-suited to complex office developments where standard prescriptive compliance would produce impractical results.
Approved Document B also applies to office buildings and provides the minimum standard required by the Building Regulations. For straightforward office buildings, compliance with Approved Document B may be sufficient. For complex or atypical office developments, BS 9999 provides a more flexible and sophisticated framework.
Modern offices present increasing fire safety challenges from fit-out. Open-plan layouts, collaboration spaces, and high-density occupancy can affect travel distances, evacuation times, and fire load. A fire strategy that accounts for the likely fit-out is essential for Cat A office buildings.
Key Fire Strategy Considerations for Office Buildings
Travel distances — BS 9999 sets maximum travel distances based on the risk profile of the building. For open-plan offices, travel distance limits may constrain floor plate design unless enhanced detection, sprinkler protection, or smoke control is provided to justify extended distances.
Evacuation strategy — most offices use phased evacuation, in which the floor of fire origin evacuates first, followed by adjacent floors if the fire escalates. The fire strategy must specify the phased evacuation zones and the alarm sequences that trigger each phase.
Sprinkler systems — while not universally required for office buildings, sprinklers are increasingly specified in larger or higher-risk office developments, both for life safety and property protection. A fire strategy that incorporates sprinklers can take advantage of code relaxations in travel distance and compartmentation.
Compartmentation — for office buildings in multi-tenanted scenarios, compartmentation between tenancies must be adequate to contain a fire within the tenancy of origin. The fire strategy must address the interface between the base build compartmentation and the tenant fit-out.
Cat A fit-out guidance — for speculative office developments delivered to Cat A standard, the fire strategy should provide guidance to tenants on the fire safety constraints within which their fit-out must operate, to ensure that fit-out works do not inadvertently compromise the fire safety design.
Frequently Asked Questions
Does an office building need a sprinkler system?
There is no mandatory requirement for sprinklers in office buildings under Approved Document B or BS 9999, but sprinklers are increasingly specified for larger or higher-risk office developments. Where sprinklers are provided, they can justify relaxations in travel distances and compartmentation that allow more flexible floor plate design.
What is phased evacuation and how does it work in offices?
Phased evacuation is an approach where occupants on the floor of fire origin evacuate immediately, while occupants on other floors are placed on standby and only evacuate if the fire escalates. It reduces the number of people using escape routes simultaneously, which is important for tall buildings. The phasing must be specified in the fire strategy and implemented through the alarm system.
Can office fit-out change the fire safety requirements?
Yes. Tenant fit-out can significantly affect travel distances, compartmentation, fire load, and the performance of smoke control systems. The base build fire strategy should provide clear guidance on the fire safety constraints within which tenant fit-out must operate, and fit-out works should be reviewed by a fire engineer to confirm compliance.
What fire resistance do office floor plates need?
The required fire resistance for office buildings depends on the building height and type. For most multi-storey office buildings, 60-minute fire resistance is standard for compartment floors and walls. Higher-risk buildings or buildings with unusual configurations may require greater fire resistance periods.
Does an office building over 18 metres need to follow the Building Safety Act gateway process?
The Building Safety Act 2022 gateway process applies to higher-risk buildings — those over 18 metres with at least two residential units. A purely commercial office building over 18 metres does not fall within the higher-risk building definition. However, the BSR oversees the safety of all buildings and the applicable building regulations still require full compliance.
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