Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants
Lawrence Webster Forrest (LWF), Fire Engineering and Fire Risk Management Consultants



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Lawrence Webster Forrest
Legion House
Lower Road
Kenley
Surrey
CR8 5NH

Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583
E-mail: fire@lwf.co.uk

Arc28 Evacuation - The Human Factor

Right click to download this fileArc28.pdf

Passive fire protection has traditionally been the first line of defence for life safety in buildings. Such measures typically include compartmentation, as well as selecting building materials and methods that will reduce the size and spread of the fire. Buildings are also designed to allow people to escape in the event of an emergency.

“Standards for fire protection in new buildings have been applied through Bylaws or Regulations for over a century. Regulatory control has mainly been achieved through a framework of prescriptive rules, which depend heavily on simple standard fire tests and Codes of Practise. Levels of performance have been arrived at and are modified largely on the basis of experience. It has been argued that prescriptive rules are highly
empirical and enforced more or less rigidly and could lead to costly over-designs.” associated with a broad range of hazards. In large or complex buildings, the design philosophy often conflicts with prescriptive regulations, so an alternative solution is required. Using performance-based (fire safety engineering) design allows us to be specific, while still observing general guidance in a benchmark sense.

A building’s means of escape should be designed so that the calculated time available before conditions become untenable (Available Safe Escape Time, ASET) exceeds the Required Safe Escape Time (RSET) needed to evacuate the building with a reasonable margin of safety.

When quantifying escape and evacuation times, we assume that time will elapse before the fire is detected (Δ tdet) and each occupant:

1. becomes aware of the fire (Δ ta)
2. recognises and reacts to the alarm ( Δ tpre)
3. travels to a place of safety (Δ ttrav).

These stages are illustrated in figure 1, comprise the total design escape time for the occupants to reach a place of safety.

The evacuation time is the interval between the time at which a warning of a fire is transmitted to the occupants of a space and the time at which those occupants are able to reach a place of safety3.

Δtevac = Δtpre + Δ ttrav

Where:

Δ tevac is the evacuation time
Δ tpre is the pre-movement time
Δ ttrav is the travel time

Pre-movement time (Δ tpre)

Pre-movement time begins at an alarm or cue and ends when travel towards an exit has begun. It has two behavioural elements for each individual occupant – recognition and response times. These determine the pre-movement time for each individual person.

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FIRE SAFETY BLOGS

  • Fire Engineering Design and Risk Assessment - Firefighting & External Water Supplies - Part 24

    In LWF’s fire engineering blog series for Architects and other professionals involved in building design, we have been looking at firefighting and, most recently, the provisions that should be made for the Fire Service to attend and put out a fire. In part 23, we looked at the requirements and recommendations relating to the provision of fire hydrants and we continue from that point in part 24.The original standards for the installation of water...

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  • Fire Safety for Healthcare Premises - Access & Facilities for the Fire Service - Part 58

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  • Fire Engineering Design and Risk Assessment - Firefighting & External Water Supplies - Part 23

    In LWFs fire engineering blog series for Architects and others involved in building design, we have been looking at the subject of firefighting. In part 22, we gave information on some of the regulations and guidance documents which deal with the issue of provision of fire hydrants. In part 23, we continue from that point by looking at who should provide them and where they should be placed in relation to the building.

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  • Fire Safety for Healthcare Premises - Access & Facilities for the Fire Service - Part 57

    In LWFs blog series for healthcare professionals, the aim is to give information on best practice of fire safety in hospitals and other healthcare premises. In part 56 of this series, LWF spent time looking at the access required by Fire and Rescue Service vehicles to healthcare buildings not fitted with fire mains. In part 57, LWF will continue looking at those measures which should be taken to ensure the Fire Service has access to...

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General Bulletins

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When we consider fire safety, our focus is normally from within, what can we do to prevent the occurrence of fire and how we can limit its damage.  Whilst this is the correct stance to take, we m...

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Technical Bulletins

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Evacuation of buildings can be analyzed in different ways. Approved Document B (ADB) which provides guidance on meeting the requirements of the England and Wales Building Regulations with regard to fi...

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