PD 7974-6:2019

What is this published document about?

This is the sixth in a series of published documents (PDs) in support of BS 7974 – a British Standard providing a framework for developing a rational methodology for designs that protect people, property and the environment from fire. The standard uses an alternative fire safety engineering approach, based on applying scientific and engineering principles.

The PDs contain guidance and information on how to undertake quantitative and detailed analysis of specific aspects of the design. They are a summary of the "state of the art" and are updated as new theories, calculation methods and data become available. They don’t preclude the use of appropriate methods and data from other sources.

This part provides information regarding engineering methods currently available for the evaluation and management of occupant behaviour. Other parts in this series include:

• Part 1: Initiation and development of fire within the enclosure of origin
• Part 2: Spread of smoke and toxic gases within and beyond the enclosure of origin
• Part 3: Structural response and fire spread beyond the enclosure of origin
• Part 4: Detection of fire and activation of fire protection systems
• Part 5: Fire service intervention
• Part 7: Probabilistic fire risk assessment

 Who is this published document for?

Primary users will be fire safety engineering practitioners. Other users include:

• Members of the fire and rescue service
• Structural engineers
• Architects
• Government departments such as the Ministry of Defence
• Universities (for teaching and research)
• Regulators
• Related industries such as insurers and systems engineers

Why should you use this published document?

It provides information regarding engineering methods currently available for the evaluation and management of occupant behaviour, particularly escape behaviour, during a fire emergency and for the evaluation of occupant condition, especially in relation to exposure to fire effluent and heat.

In most cases of fire, this involves evacuation of the occupants. A basic principle of a performance-based (fire safety engineering) building design is that the available safe escape time (ASET) is greater than the required safe escape time (RSET) by an appropriate margin of safety. An appropriate margin of safety takes account of the risks associated with different potential fire scenarios and the uncertainties in the prediction of ASET and RSET for particular design scenarios. Uncertainties for specific ASET and RSET parameters are considered in this Published Document. Assessment of overall safety margin for a design is considered in BS 7974.

An ideal fire safety design ensures that building occupants are able to reach a place of relative or ultimate safety without ever coming into contact with or even being aware of fire effluent and/or heat. This is the main design criterion for the safety of the majority of occupants in multi-compartment buildings (see BS 7974 and BS ISO/TR 13387-8). A major design criterion is therefore the estimation of the time required for escape in situations where occupants are not directly affected by fire effluent or heat.

What’s changed since the last update?

This is the first revision of Part 6 since its original publication in 2004. It has been brought fully up to date to reflect changes in the industry, as well as to BS 7974 and other parts in the series. The main changes are:

• The principal guidance and bibliography have been updated in line with recent developments and publications since 2004
• The data tables in the Annexes have been expanded to include more recently published data and bibliography
• A full set of expressions has been provided for fractional effective dose calculations with worked examples to illustrate the calculation methods