The LWF Blog

Fire Safety for Facilities Management Personnel – Gaseous System Agents – Part 251

May 7, 2024 11:56 am

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 250, LWF discussed gaseous suppression and total flooding systems. In part 251, we continue discussing halocarbon and inert gases used in total flooding applications.

Inert gas agents used in suppression systems and total flooding applications work by extinguishing flames through physical means. Essentially, they reduce oxygen concentration to the point at which combustion cannot be sustained. In the same manner as CO₂, much higher concentrations of the gas are required to achieve the same effect as halon 1301 or the halocarbon agents. Despite the need for more product to be used, inert gas agents are safer than CO₂, because the oxygen level remaining is sufficient to support life.

There are four inert gas agents in common use, as follows:

• IG-541 (52% nitrogen, 40% argon, 8% CO₂)
• IG-55 (50 % argon, 50% nitrogen)
• IG-01 (100% argon)
• IG-100 (100% nitrogen)

The choice of agent, inert gases or halocarbons, may be influenced by the following factors:

• Inert gas agents, unlike halocarbons, can’t be stored as liquefied gases. They must be stored at high pressure (200/300 bar, dependent upon which) resulting in more containers being required.
• Halocarbon agents, while not ozone depleting, still have extended atmospheric lifetimes and contribute towards global warming. Inert gas agents have naturally occurring contents.
• When inert gases are discharged into a room, significant overpressures are created which can mean it’s necessary to install pressure relief vents. However, in the case of a well-sealed enclosure, the same may be said of halocarbon release.
• Mechanical extraction systems may be required for both halocarbon and inert gas agents, for different reasons. Halocarbon agents are broken down by flames and hot surfaces and result in decomposition product which is acidic and may cause corrosion if not removed quickly. For this reason, when using halocarbon agents, mechanical extract is essential. Inert gases do not produce acidic breakdown products, but mechanical extract is preferred to remove smoke and soot deposits distributed around the room by the force of the inert gas discharge.
• To prevent fire re-ignition, the extinguishing gas should be held for a period of time after it is discharged. A well-sealed enclosure is usually required. In the case of inert gas, the density of the gas/air mixture is close to that of air. As a result, the leakage is slower and the extinguishing gas can usually be held for longer durations.

 

In part 252 of this series, LWF will continue to discuss inert gases and halocarbons, as well as the relevant design codes. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 35 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.

 

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.