The LWF Blog

Fire Safety for Facilities Management Personnel – How fire works – Part 59

August 17, 2020 12:22 pm

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 58, LWF discussed the combustion of flammable liquids. In part 59, we will discuss the combustion of flammable gases.

When it comes to the way in which they combust, there is little difference between the vapours from substances which are liquid at normal temperature and pressure, and flammable substances which are gaseous at normal temperature and pressure.

With gases, the question of flashpoint doesn’t arise, of course, and an indication of the hazard posed by the gaseous substance may be ascertained from the flammability limits.

As with flammable liquids, the auto-ignition temperature ranges between 200 ºC and 600 ºC for most flammable gases and the indication is of a lesser significance than other markers.

In most commercial and industrial environments, flammable gases, rather than those used for heating or cooking, will be rarely found. However, when a contractor is on site, undertaking activities such as cutting and welding, acetylene or liquefied petroleum gas (LPG) can often be used. LPG is sometimes used for temporary heating or as a fuel for tar boilers.

Acetylene has very wide flammability and explosive limits and is potentially unstable. LPG has much narrower flammability limits but its own particular hazard lies in its density, which is greater than that of air. This means that the gas can accumulate in low-lying areas, such as basements, pits and drains.

Leakage from LPG cylinders, for instance, can remain undetected until an ignition source causes flame to flash back to the cylinder itself.
Whichever and whenever gases are used in your premises, whether it be for a permanent function or due to contractors on site, it is essential that a risk assessment is completed and the risks mitigated as much as possible. Changes to working practices, as well as physical changes to the building, can impact upon the validity of a previous fire risk assessment and result in un-anticipated fire hazards. It is essential that all changes are considered, addressed and detailed within a fire risk assessment.

In part 60, LWF will begin to look at the mechanism of extinguishment – how fires can be put out, in essence. 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 25 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.