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Portable fire extinguishers are often the first line of attack in tackling fires before they get out of control. Joseph Milton guides us through their development and use.
At the beginning of the 20th century in town centres around the country, wooden structures were set alight in front of an audience. A salesman would then put out the fire using a fire extinguisher and proceed to sell extinguishers to members of the public.
Anybody who has witnessed fire testing of extinguishers might arrive at the conclusion that little has changed since. We still set fire to wooden cribs, though not now as a selling tool but rather to test the extinguisher’s ability to put out the fire, as stated in EN3.
The first recognised extinguisher was invented in 1715. It was a wooden barrel that contained 20 litres of water along with gunpowder and a fuse. It was thrown onto the fire and the explosion extinguished the fire. The following highlights how extinguishers, as we know them today, have developed since then:
– 1816 saw the invention of a cart mounted copper vessel containing pearl ash liquid (potassium carbonate, still used in wet chemical extinguishers) which was discharged by compressed air.
– In the 1850s dry powder was introduced as an extinguishant.
– By 1866 the first soda-acid extinguisher was invented. Operation was by a chemical reaction producing carbon dioxide gas used to expel the contents.
– In 1882, a patent was granted for the storage of liquid carbon dioxide in steel bottles.
– In the early 1900s the first carbon dioxide gas cartridge extinguisher with external cartridge was invented.
– In 1912, the carbon tetrachloride extinguisher was invented for use on petrol and fires involving live electricity. There were deaths from the use of this extinguisher in confined spaces because the vapour and combustion caused toxic by-products.
Since the introduction of fire extinguishers, two basic operating types have evolved: stored pressure and gas cartridge. A stored pressure extinguisher normally has a pressure gauge (except carbon dioxide), so when the valve is opened the pressure forces the contents out of the extinguisher. A gas cartridge extinguisher, (which does not need a pressure gauge) is operated by piercing an internal gas cartridge which pressurises the extinguisher. The extinguisher then operates as a stored pressure extinguisher.
Extinguisher standards
EN 3 is the European Standard for portable fire extinguishers and currently there are three parts to it:
– Part 3 Construction, resistance to pressure, mechanical tests.
– Part 6 Provision for the conformity of portable fire extinguishers in accordance with EN 3 Parts 1 to 5
– Part 7 Characteristics, performance requirements and test methods.
Originally in 1996 when this standard was published, there were six parts. Part 7 was published in 2004 and supersedes parts 1, 2, 4 and 5 (now withdrawn). The following parts of EN 3 are drafts and are currently in development:
– Part 8 (draft) Additional requirements to EN 3 for construction, resistance to pressure and mechanical tests for extinguishers with a maximum allowable pressure equal to or lower than 30 bar.
– Part 9 (draft) Additional requirements to EN 3 for pressure resistance of CO2 extinguishers
– Part 10 (draft) Provisions for evaluating the conformity of a portable fire extinguisher to EN 3 Part 7.
Fire extinguishers display the classes of fire for which they are suitable, the classes are letters A, B, C etc. The classification of fires (BS EN 2) lists the classes of fire as follows:
Class A: for use on flammable solid materials, such as wood, paper, coal, straw and cloth. Combustion normally involves the formation of glowing embers. The most successful method of extinguishing this type of fire is by cooling, so a water extinguisher would normally be chosen for this risk. This type of fire can also be extinguished by smothering or starving the fire of oxygen. A foam or ABC powder extinguisher would be chosen for this reason.
Class B: for use on fires involving flammable liquids or liquefiable solids. Examples of flammable liquids are petrol, methylated spirits, paraffin and paints. Examples of liquefiable solids are grease, lard, margarine and shoe polish. This type of fire is extinguished by smothering and starving the fire of oxygen, so a foam, dry powder or carbon dioxide extinguisher could be used.
Class C: for fires involving gases. Examples of flammable gases are propane, acetylene and butane. If there is a gas leak, the fire should be extinguished by closing the gas valve. It cannot be over emphasised that training is crucial when dealing with this type of fire. If for safety reasons the valve cannot be closed, dry powder BC and ABC is recommended. It is at the manufacturer’s discretion to decide whether to mark an extinguisher as suitable for use on a Class C type fire. EN3 only permits powder extinguishers to be marked with a class C after they have achieved a B fire rating (BC powder) or A and B fire ratings (ABC powder).
Class D: for fires involving metals, for example, magnesium, sodium, cadmium and manganese. These fires are usually extinguished by smothering and specialist advice is needed to provide suitable extinguishers, because these types of fires can be very dangerous. These fires are extinguished by specialist dry powders extinguishers incorporating a low velocity applicator.
Class F: for use on cooking oil fires. Examples of cooking oils are rapeseed, palm; vegetable, sunflower and olive and these types of fire are extinguished by cooling and smothering. The discharge cools the flames, while the formation of a foam blanket smothers it. Wet chemical (potassium salts) extinguishers are chosen for this risk.
Accreditation
LPCB has an extensive range of UKAS accredited fire testing facilities to conduct both Class A and Class B fires to EN 3. It also offers fire testing and approval of portable fire extinguishers to BS 7937 (portable fire extinguishers for use on cooking oil fires to Class F) and to BS 6165 (small aerosol fire extinguishers). The Marine Equipment Directive (MED), the Pressure Equipment Directive (PED) and the Transportable Pressure Equipment Directive (TPED) are Directives that are all applicable to fire extinguishers. BRE is also a Notified Body for all three of these Directives.
Approval, also known as certification, is independent third party confirmation that products, like fire extinguishers, meet and continue to meet appropriate standards. Organisations such as LPCB which offer this service must be UKAS accredited for third party certification and testing of portable fire extinguishers. Approval is different from a test: through regular audits it ensures that extinguishers continue to comply with the prevailing standards which can be subject to revision and replacement. The auditing process also helps to confirm that the extinguisher available on the market place is exactly the same as that which was originally tested and approved.
Globally, specifiers are demanding third party approval. The LPCB mark is recognised worldwide and helps to confirm that products meet and continue to meet standards and specifications. For a full list of
LPCB approved products please visit www.redbooklive.com
Joseph Milton is scheme manager at LPCB
NOW WE’RE COOKING
One of the UK’s largest insurers is advising that Class F, wet chemical extinguishers should be present in cooking environments to specifically combat hot oil fires.
Insurance giant AXA carries out around 20,000 inspections of commercial premises annually through its in-house survey team. Many of the businesses inspected involve cooking risks, notably deep fat frying within restaurants and workplace kitchens. A central feature of the inspections is to ensure that effective housekeeping measures are taking place such as regular cooking oil changes, use of extraction systems and the implementation of rigorous cleaning regimes. Also part of the inspection process is to check that appropriate portable fire extinguishers are in place and, for situations involving deep fat drying equipment with over three litres of oil, this means Class F extinguishers which comply to BS 7937:2000. In addition, AXA advise the installation of fixed gaseous systems on the larger or more frequently used cooking risks, which should comply to Loss Prevention Certification Board (LPCB) LPS1223 and be installed and maintained by their authorised agents.
Rob Dakin, risk control at AXA comments: “The Regulatory Reform (Fire Safety) Order will further reinforce the need for appropriate extinguishing systems as an integral part of any fire risk assessment.”
AXA has also specified that maintenance of portable extinguishers by a BAFE Registered Technician is a condition of compliance with its warranty of deep fat frying equipment. The following clause is taken from the AXA warranty:
“A 6-litre Class F wet chemical fire extinguisher is situated where it is easily accessible in the vicinity of any deep fat frying equipment and is maintained under an annual service contract with a BAFE registered contractor.”