The LWF Blog

Means of Escape Series – Part 3 – Fire Engineering Solutions

April 2, 2014 9:39 am

The means of escape series has looked in some detail about how the evacuation procedure for a build should be decided during the design phase. This third part discusses how fire engineers can help to provide a fire safe solution to evacuation challenges, where the proposed design would fall outside the prescriptive guidance.

The Fire Safety Engineering Approach

Where design standards provide recommendations based on building types, i.e. all offices buildings, shops, restaurants, cinemas, etc, the fire safety engineering approach considers every building (and not type of building) individually. It may therefore be acceptable to justify an extended travel distance in the design of a shop 1 using an approach A, but it may totally be unacceptable to apply that solution to the design of a shop 2.

The evacuation process can be broadly broken into three parts that take place one after the other: 

Recognition time

Response time

Travel time

The Recognition Time is the interval between the time at which a warning of a fire is given and the first response to the warning.

The  Response Time is the interval between the time at which the first response occurs and the time at which the first move is made towards an exit.

The Travel Time is the time needed, once movement towards an exit has begun, for all occupants of a specified part of a building to reach a place of safety.

The various elements of the building’s overall fire strategy are linked and will therefore impact upon one another. The escape width and travel distance will have a major impact on the travel time during an evacuation. Similarly, the fire detection and alarm system will have an impact on the recognition time. Staff presence and management will impact upon the response time.

As with the rest of the fire safety precautions usually installed in a building (e.g. fire alarm system, fire suppression system, etc.), the means of escape design may be proven adequate for life safety, even though it is not compliant with recommended design standards, on the basis that compensatory features are provided. Hence, it may be acceptable to have an extended travel distance in a building if a sprinkler system is installed in that building, for example.

Computer Models

In order to assist in the design of means of escape, a number of computer models have been developed. These allow the designer to establish a building geometry, specify the escape route, final exit doors and their respective widths. Once these parameters are in place, the software requires the input of occupants: numbers, locations, direction of escape, etc. 

Most software also takes into consideration whether the occupants are adults, children, elderly or people with disabilities, by allowing the designer to specify the walking speed of each occupant. 

Once the setup is in place, the simulation is run and provides various outputs such as the total building evacuation time, a specific room evacuation time, the number of people to evacuate through a specific fire exit door, etc. 

Further to analysis of the results, alterations of the parameters are made (reduction of travel distance by moving an exit door, increase in the width of an exit route, etc.) and the simulation is run again. Computer models are tools that require a high level of expertise in order to design or review means of escape design. They are increasingly used by fire engineering consultancies on behalf of clients to provide justification and fire safety of means of escape designs which do not meet the prescriptive guidances.

If you would like to discuss this blog in more detail or discuss your own project, please contact Peter Gyere on 020 8668 8663.

LWF are fire engineering and fire risk management consultants with over twenty five years experience in the development of fire engineered technology and the application of fire safety standards including fire engineered techniques.