KFC – Keep Frying correctly
July 15, 2010 by admin
Filed under Extinguisher Types
Frying tonight – the ‘f’ class fire classification
Over 10 years ago a new classification of fire was introduced for fires involving cooking oils, however there is still some ignorance around the need to have specialised equipment to safely tackle fires in this category and many establishments remain unprotected against this dangerous fire risk
Classifications
For fire fighting purposes fires have been classified, first under BD 4547 and now EN2, according to the main type of fuel involved.
Class A – fires involving flammable solids
Class B – fires involving flammable liquids and liquefiable solids
Class C – fires involving flammable gases
Class D – fires involving flammable metals
Class F – fires involving cooking oils and fats
There used to be a Class E for electrical fires, but this was discontinued as electricity doesn’t burn – an electrical fire can involve any of the above classes, with the presence of electricity being an additional hazard rather than a fuel. Fires where electricity are present are still categorised separately on extinguisher labels so that a non-conductive agent that is safe for use where a live electrical supply is involved can be identified.
Cooking oils and fats were traditionally part of Class B, along with substances like petrol and spirits. However a major difference in how they burn means that normal agents for Class B fires are ineffective. Most flammable liquids, such as petrol or heptane (which is used for fire test rating of Class B extinguishers), burn around 50 degrees Centigrade. However, cooking oil fires commonly start when the oil is heated to past it’s auto-ignition temperature, usually between 285 & 385 degrees Centigrade, but sometimes up to 499 degrees Centigrade. The oil burns at this temperature, but it’s auto-ignition temperature is reduced (by this burning) by about 30 degrees Centigrade. Thus, the fire will be self sustaining unless it’s temperature is significantly reduced. This high temperature makes the fires very dangerous and presents problems when trying to use normal extinguishing methods on these fires. A tble at the end of this article summarises the problems with traditional agents.
Case studies
The following case studies illustrate the problem when using traditional agents.
- South Mimms Service Area – A fast food restaurant’s fryer caught fire and was immediately tackled with CO2 extinguishers. These had no effect and the fire spread to the ductwork. The entire service area burnt down as a result.
- Heathrow Terminal One – A fast food restaurant’s fryer caught fire and was immediately tackled with CO2 extinguishers. These had no effect and the fire spread to the ductwork. The terminal was severely damaged. Millions of pounds were lost through damage and disruption.
- Royals Shopping Centre – A fryer caught fire in one of the units and was immediately tckled with two fire blankets. One was too small, the other burnt through. Despite the rapid attendance of the fire service and the use of a fixed BC Powder extinguishing system the fire was only just contained with great difficulty.
Following lobbying by the fire industry, Class F, a new fire classification, was introduced for all fires involving cooking oils.
A new symbol for use on extinguishers, depicting a burning frying pan with the letter F in the top right corner, was also introduced.
The only type of extinguisher to be Class F rated is the Wet Chemical extinguisher. This contains an alkaline liquid solution of up to 20% potassium salts (potassium acetate, potassium citrate, potassium carbonate) and it is the unique effect of these salts on the fats in cooking oils that is the key to their effectiveness.
Wet Chemical saponifies the oil, i.e. by hydrolysis rapidly converts the burning substance to a non-combustible soap. This process is endothermic, meaning it absorbs thermal energy from its surroundings, decreasing the temperature and eliminating the fire. The soapy scum formed also secures vapours and generates steam, assisting the extinction further.
Even a raging fryer with 75 litres of oil can be extinguished in under 2 seconds, however the entire extinguisher must be discharged onto the oil to ensure a complete crusting of the surface and maximise cooling.
Potassium salts had been used in the US for many years in the form of ‘loaded stream’ extinguishers for greater effectiveness on Class A fires and it was the US who developed the first Wet Chemical extinguishers for cooking oil fires in the 1990’s
Chubb Fire first introduced US made Badger Wet Chemical extinguishers to the UK in the late 1990’s, followed by the UK base of the US firm Amerex and currently there are several manufactures of these extinguishers around the world.
In the UK Wet Chemical extinguishers are made to BS 7937: 2000 and are identifiable by a Canary Yellow panel to the front of the extinguisher and the class F symbol. They bear a Fire Rating based on the maximum size, in litres of oil, the extinguisher can extinguished when used by a skilled operator. A typical 6 or 9 litre extinguisher would be rated 13A:75F (the water base makes it suitable for Class A fires as well)
Because they discharge as a fine mist they pass the 35kv conductivity test for extinguishers and can be used in the presence of energised electrical equipment, although care needs to be taken with pools of agent on the floor.
The cost of the agent makes them slightly dearer than traditional extinguishers and to make them available to smaller establishments are produced in a range of sizes with ratings from 25F to 75F. The German manufacturer Total has a compact 2 litre model with an impressive 40F rating.
Comparison of agents
| Extinguishing media | Effectiveness on Class F fires |
| Light duty fire blanket BSEN1869 | Only tested and effective on small cooking oil fires up to 3 litres and containers of no more than 345mm diameter.
Difficult to apply as requires getting close to the fire. Can eventually burn through or sink into the burning oil |
| Water/water additive | Water mixes with the fat, boils and the steam ejects burning fat |
| Aspirated Foam Branchpipe | Used to be used in kitchens, not commonly available now. Requires skilled application and high delivery rates as the extreme heat destroys the foam blanket |
| Foam Spray | The extreme heat breaks up the extinguishing film preventing it sealing off the fire |
| CO2 | The gas is readily dispersed by the air currents produced by the raging fire and the lack of cooling action means the oil remains at auto ignition temperature |
| ABC Dry powder (Acidic Ammonium Phosphate) | In virtually all current powder extinguishers. Being acidic cannot saponify the oil and although the flames may be temporarily knocked down the oil reignites as the extinguisher runs out |
| BC Dry powder (alkaline sodium bicarbonate) | Used to be used in most powder extinguishers and does have some effect, but requires several larger extinguishers and there is a re-ignition risk |
| Halon 1211 BCF | Illegal except for exempted special users. |
FE-36 Clean Agent
August 4, 2008 by admin
Filed under Extinguisher Types
With the worldwide ban on Halon 1211, the race was on to create a clean, safe alternative for use in highly sensitive areas. As a result, the US manufacturing giant DuPont created FE-36, or Hydrofluorocarbon-236fa (HFC-236fa).
FE-36 works almost as effectively as the illegal halon, is less toxic, and does not deplete the ozone layer. FE-36 also leaves no residue, is non-corrosive, non-conductive, and will not cause thermal shock damage to machinery.
How Fire Extinguishers Containing DuPont FE-36 Work
These extinguishers discharge a stream of gas and liquid droplets that are propelled into the heart of the fire, stopping combustion through a chemical reaction and by absorbing the fire’s heat.
Since FE-36 becomes a gas at -1.4 degrees C (39 degrees F), it leaves no residue behind and after the fire, dissipates into the atmosphere. FE-36(tm) fire extinguishers can be used on fire classes A and B, and directly on electrical equipment.
FE-36 Fire Extinguishers in Europe
Although not yet widely available in the UK and Europe, these extinguishers are used in medical facilities across the USA. In addition, portable fire extinguishers containing FE-36 can be used in sensitive locations such as computer rooms, document stores, clean rooms, telecommunications facilities, control rooms, switch rooms, marine craft and installations, banks, museums, archives, laboratories, and airplanes.
The most common range of fire extinguishers containing FE-36 are Cleanguard extinguishers from Ansul.
In the UK Today
Motorsport participants might also be interested in the Zero 360, an FE-36 extinguisher especially for high performance racing and rally cars from Lifeline.
Also seen in small automatic extinguishers, the defunct Firemaster company’s previous management have set up a new company called Fireblitz Extinguisher and are now supplying 1kg and 2kg automatic sizes again.
“Total Flood” Fire Suppressant Systems
DuPont FE-36 can now be used to replace Halon 1301 in fixed fire protection systems. Fire extinguisher systems with FE-36 come into their own where a ‘total flood’ fire suppressant system is required. This involves ‘flooding’ an entire room or enclosed area with sufficient fire fighting agent to extinguish the fire. (If CO2 gas were used instead, the volumes involved would prove fatal to anyone in the area.)
FE-36 and Hydrogen Fluoride
When combusted, under certain conditions, FE-36 can produce hydrogen fluoride (HF). Whilst this gas is generally produced in small quantities, and the gas itself boils just below room temperature, you should make sure that after a fire, the area is fully ventilated before staff return.
You should also avoid breathing in any fumes from an FE-36 extinguisher treated fire, as on contact with moisture, including human tissue, hydrogen fluoride converts to hydrofluoric acid. This acid is highly toxic and corrosive.
MRI-Safe Fire Extinguishers
August 4, 2008 by admin
Filed under Extinguisher Types
MRI-safe fire extinguishers are designed to protect these expensive and life-saving machines from damage in the event of a fire. High specification CO2 fire extinguishers and water mist extinguishers are designed with non-magnetic components to be able to operate in the vicinity of a magnetic resonance imaging (MRI) machine.
How MRI-Safe Fire Extinguishers Work
MRI-safe fire extinguishers are essentially the same as normal extinguishers on the inside. However, MRI-safe fire extinguisher cylinders must be non-magnetic, as the magnetic field of an MRI machine is strong enough to attract a normal fire extinguisher with bone-crushing force.
It is not often realised but the magnetic potency of an MRI machine stays for a long time after it is turned off. This prevents fire-fighters from entering with something as simple as a metal belt buckle. There have been incidents of people being “sucked” into an MRI with tragic results.
The same rule applies to any machinery with a strong magnetic field, such as nuclear magnetic resonance spectrometers (NMR’s). Non-magnetic fire extinguishers should also be used in health centres, clinics, and any premises where magnetic interference might affect the performance or operation of sensitive equipment.
Non-magnetic fire extinguishers are made with a non-magnetic stainless steel or aluminium shell, and non-magnetic fittings such as valves, nozzles and pins.
Specially manufacturerd 2kg CO2 fire extinguishers are the most popular non-magnetic type in the UK, since they can be used to extinguish fires in, on or around electrical equipment, are clean to operate and do not leave any residue after use. The non magnetic fire extinguisher is are available online from Fire Protection Online and is made by Chubb Fire (and also sold under their sister company name of Thomas Glover).
Water Mist Fire Extinguishers
Amerex Corporation of the USA developed their water mist extinguisher for use in clean rooms, telecoms areas and health care facilities. Using distilled water instead of tap water, it has a specially-developed misting nozzle that atomizes the water making it non-conductive.
These are available in 1.75 gallon and 2.5 gallon size but, due to the cost of testing weighed against the demand, are not tested in the UK to BS EN3. However, they have full UL approval in the USA.
As you can imagine, high specification non-magnetic fire extinguishers do not come cheap, retailing at a premium to the standard models. But, they can be found online at much lower prices.
Know Your Extinguishers
August 3, 2008 by admin
Filed under Extinguisher Types
In the event of a fire, using the correct extinguisher to put it out is as important as discovering the fire itself. All modern fire extinguishers are clearly marked as to the type of fire they should be used on, so you can tackle small fires safely and easily.
Different Fires Require Different Fire Extinguishers
It sounds obvious, but different types (or classes) of fire require different extinguishers. For example, a water-based extinguisher is ideal for use on free-burning materials such as paper or wood, known as a Class 1 fire. For full details, see our in-depth guide to fire extinguisher types
UK Fire Extinguisher Markings and Colours
All fire extinguishers are colour coded for easy recognition in an emergency. They also have ratings as to which class of fire they can be effective in extinguishing, so you can double-check that you have the right fire extinguisher for the job.
In addition all fire extinguishers should bear quality standard marks, such as the familiar BS Kite Mark and CE Mark. For full details on classes of fires and extinguisher ratings, see the detailed guide to fire extinguisher fire ratings and multi-rating fire extinguishers
A Fire Extinguisher in the Hand
A fire extinguisher is only truly effective when you, the person picking it up in an emergency knows the best way to use it! Our handy guide to how to use a fire extinguisher takes you through simple steps for efficient fire extinguisher use.
Fire Extinguisher In-depth Guides
The best and clearest fire extinguisher information, right here at your fingertips.