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

Fire Engineering Design and Risk Assessment - Gaseous System Configuration - Part 10

Posted by LWF: 05/07/2018 14:44

In LWF’s fire engineering blog series for Architects and others in the building design business, we have been looking at those systems designed for fire suppression. In part 9 an introduction to gaseous systems was made and in part 10, gaseous system configuration will be discussed.

A gaseous system is a fire suppression method which involves the active agent being released from containers into a distribution pipework. The system may comprise one or more containers which can be made operational by an electrical signal, pneumatically or manually. 

The distribution pipework is usually kept empty and is made of steel. Nozzles are mounted at appropriate intervals which allow the agent to be distributed in a uniform fashion upon discharge. Release from each nozzle will usually happen simultaneously.

While a small, one-canister system may be pre-engineered with no flow calculations or nozzle sizing necessary, most systems are engineered for purpose to take into account distribution and discharge duration.

The container valves are designed to be opened by a separate actuation system, most commonly this would be an automatic system, the purpose of which is to detect fire and activate the gaseous system.  The detection system will also be able to trigger the fire alarms and shutdown any plant or equipment which might provide sources of ignition or fuel to further the fire. A manual release will also be included.

The element of the system which deals with fire detection should be designed to be in line with current British Standards. Typically, this would mean each hazard area including two zones of smoke detectors which are arranged so that the first detector would sound an alarm and two detectors would sound ‘pre-discharge’ alarms. The two-detector alarm would also trigger the commencement of a timer countdown which was set to suit the necessary evacuation time required. As the timer completes, a distinctive discharge alarm would sound and at the end of the ‘pre-discharge’ alarm, the gaseous agent would be activated and released.

Alternatively, a total flooding system may be used. This comprises a gaseous release system which is contained within an enclosure of reasonable integrity to avoid the escaping of the gas into other areas. Upon release, the gas is contained within the area to build up and maintain sufficient fire extinguishing concentration throughout the area and for a sufficient amount of time to allow the extinguishing of the fire and to allow potential sources of re-ignition time to cool. 

The halon replacement gaseous clean agents are considered suitable for surface fire hazards, whereas only CO2 has design criteria and standards for deep-seated fire risks. 

In cases where a local application system is used for hazards which are small in relation to the surrounding area, the gas is only applied to the hazard itself. In this situation, the halon-alternative gaseous clean agents are unsuitable and only CO2 has the necessary design criteria and standards.

In part 11 of this series, LWF will look at the agents used for gaseous systems. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.

While care has been taken to ensure that information contained in LWF's publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.

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