The LWF Blog
Fire Engineering Design and Risk Assessment – Halocarbon Agents – Part 12July 19, 2018 12:08 pm
In LWF’s fire engineering blog series for architects and others in the building design business, we have been looking at Fire Suppression and most recently, gaseous systems. In part 11, we looked at the effect of gases on the environment and in part 12, we’ll discuss halocarbon agents and inert agents before touching on water mist systems.
Halocarbon agents were developed as a viable alternative to halons after the substance was banned for general use due to the potential damage to the environment. Those halocarbons which are in general use are detailed in BS EN 15004 – Fixed firefighting systems. Gas extinguishing systems – a multi-part guidance document on the subject of gas extinguishants.
Halocarbon systems can discharge in 10 seconds, which is comparable to the release time for halon. This allows the gas to reach the extinguishing concentration level quickly, which helps to avoid decomposition of the agent by the fire.
Inert gases are comprised of naturally occurring elements and so are not subject to the Kyoto Protocol. There are various inert agents or mixtures of inert agents available for use, made up of the following substances:
Argotec is wholly argon.
A 50/50 mix of nitrogen and argon is called Argonite.
Inergen is a 52/40/8 mix of nitrogen, argon and CO2. In the case of Inergen, the CO2 is included to stimulate an increased oxygen intake in environments where oxygen levels are low.
The performance of inert agents and minimum design concentrations can be found in BS EN 15004, linked above. The time for an inert agent system to discharge is around one minute which, while it seems much longer than halocarbon agents, would usually result in the extinguishing of the fire in that time.
Water Mist Systems
Guidance documents on the use of water mist systems are available as follows:
BS 8489-1:2016 – Fixed fire protection systems. Industrial and commercial watermist systems. Code of practice for design and installation
NFPA 750 – Standard on Water Mist Fire Protection Systems
Water mist systems differ from sprinkler systems due to the fine nature of the spray. The NFPA define it as ‘fine water sprays for the efficient control, suppression or extinguishment of fire using limited volumes of water’. A fine spray is one where 99% of the droplets are less than 1000 microns in diameter.
Water mist systems are generally suitable for use in enclosures up to 5m high with low to medium levels of ordinary combustibles. They are most commonly used in shops, hotel rooms and offices. In addition, water mist systems can be used in EDP areas, cable tunnels and where there is the potential for flammable liquid fires.
In part 13 of this series, LWF will continue looking at water mist 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.