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

Facilities Management & Fire Safety - Gaseous Systems - Part 24

Posted by LWF: 06/09/2017 16:18

In LWF’s blog series on fire safety for those who work in Facilities Management, we have been looking at the use of gaseous systems as a fixed fire protection system. In Part 23, we established that since halon was phased out in 2003, CO2 systems continued to be used and in recent years, two new categories of gaseous agents were established – halocarbons and inert gases. In Part 24, we’re going to look at the differences between inert gases and halocarbons, as these differences may influence your choice of agent and system.

Inert gas agents cannot be stored as liquefied gases and must be stored at high pressure of around 200 bar and 300 bar. This means that more containers will be required for storage than a halocarbon system.

Halocarbon agents often have long atmospheric lifetimes and so can contribute towards global warming (however they do not damage the ozone layer like halon). Inert gases do not have any impact on global warming as they are comprised of naturally occurring constituent parts.

The overpressures created by the release of inert gases into a room are such that pressure relief vents may need to be installed to combat the effects. However, this can also apply to an enclosed area into which halocarbons are released too.

Halocarbon agents once released are broken down by fire and the resultant hot surfaces. As the decomposition products produced are acidic, they can cause corrosion if not cleared promptly. For this reason, mechanical extraction will be necessary. Although inert gases do not require clearing for the same reason, as there is no acidic residue, the force of the discharge will cause excessive smoke and soot deposits and so mechanical extract is still a likely requirement.

As extinguishment of the fire requires that the gas is held in the affected area, the area must be well sealed to avoid leakage of the agent away from the area of danger. This will avoid re-ignition of the fire as the gas disperses. In the case of inert gas, the leakage would be slower than with halocarbon agents, as the density of the inert gas/air mixture is closer to that of simple air.

Although this was covered in previous blogs, it is worth re-asserting the dangers of exposure to CO2 should such a system be in use. Such systems should only be used in specialist areas which will be empty of occupants and the gas must be thoroughly cleared before it is safe to re-enter. Failure to adhere to such safeguards can lead to fatalities.

Exposure to inert and halocarbon gases is undesirable, but the low levels of toxicity mean that short term exposure would not be seriously debilitating. To avoid exposure, any people in the area where the gas is to be released should be given warning to evacuate the area and in cases where this is likely to be a concern, controls to allow occupants to delay gas release manually should be placed in the area.

In Part 25, we will discuss the design codes affecting gaseous systems as well as exploring the components of an installation. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact Peter Gyere in the first instance on 0208 668 8663.

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 25 years' experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.

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