Extinguishers - not just a bottle with a pin

Published:  01 October, 2005

There are two salutary lessons about extinguishers to be learned from events in 2005, explains Vince Grenadine.

There are two salutary lessons about extinguishers to be learned from events in 2005, explains Vince Grenadine.
The first happened in the UK on May 25th, 2005: A father and son whose car burst into flames after veering off a motorway were saved by a passing fire extinguisher technician.
The pair suffered serious head injuries and were trapped when their car hit a roadsign on the M23 motorway in West Sussex.  The car immediately caught fire but the flames were put out by Jon Paxton, a passing service engineer, armed with three full-sized fire extinguishers.
West Sussex Fire and Rescue station officer Gary Towson told IFJ: “They might not have survived at all if it wasn’t for the swift actions of the motorist with his extinguishers.”
On March 10th, 2005, six people died and more than 90 others suffered burn injuries in a fire on a ship - the PNS Moawin - an auxiliary vessel which serves as one of two fleet tankers. The vessel was reported to be badly damaged and is currently  docked in the southern Pakistani city of Karachi.
A ‘fireball’ apparently engulfed the logistics vessel during routine maintenance and cleaning work, initiated by a small ‘hotwork’ fire which was not controlled.
Media sources suggest that onboard fire extinguishers were not available for workers to use as they had been removed for overhaul. The onboard inert gas fire supression system was also apparently down for maintenance.
“The fire was extinguished by fire teams with hoselines before the situation escalated any further,” a navy spokesman told IFJ. “I cannot comment on any reports about emergency extinguishers being unavailable.”
A major security ring has been thrown around the incident. A spokesman said the fire was an accident. “It occurred because of human error. The fire occurred about a week after Pakistan and neighbouring Iran held joint naval exercises in the Arabian Sea.”
So - the point of these two radically different incidents is clear. Lives were saved when extinguishers were to hand; lives were lost when they weren’t. It seems a blindingly obvious lesson which people still need to learn.
What do you need to know?
There are basically four different types or classes of fire extinguishers you should be aware of, each of which extinguishes specific types of fire. Newer fire extinguishers use a picture/labelling system to designate which types of fires they are to be used on, writes Dr. Rob Toreki, president of Interactive Learning Paradigms, Inc.
Older fire extinguishers are labelled with coloured geometrical shapes with letter designations. Additionally, Class A and Class B fire extinguishers have a numerical rating which is based on tests conducted by Underwriter’s Laboratories that are designed to determine the extinguishing potential for each size and type of extinguisher.
In the US, for example, the National Fire Protection Association (NFPA) classifies fires into five general categories (U.S.):
z Class A fires are ordinary materials like burning paper, lumber, cardboard, plastics etc.
z Class B fires involve flammable or combustible liquids such as gasoline, kerosene, and common organic solvents used in the laboratory.
z Class C fires involve energised electrical equipment, such as appliances, switches, panel boxes, power tools, hot plates and stirrers. Water is usually a dangerous extinguishing medium for class C fires because of the risk of electrical shock unless a specialised water mist extinguisher is used.
z Class D fires involve combustible metals, such as magnesium, titanium, potassium and sodium as well as pyrophoric organometallic reagents such as alkyllithiums, Grignards and diethylzinc. These materials burn at high temperatures and will react violently with water, air, and/or other chemicals. Handle with care!!
z Class K fires are kitchen fires. This class was added to the NFPA portable extinguishers Standard 10 in 1998. Kitchen extinguishers installed before June 30, 1998 are “grandfathered” into the standard.
Some typical extinguishers and their uses include:
z Water extinguishers are suitable for class A (paper, wood etc.) fires, but not for class B, C and D fires such as burning liquids, electrical fires or reactive metal fires. In these cases, the flames will be spread or the hazard made greater. Water mist extinguishers are suitable for class A and C.
z Dry chemical extinguishers are useful for class ABC fires and are your best all around choice. They have an advantage over CO2 extinguishers in that they leave a blanket of non-flammable material on the extinguished material which reduces the likelihood of reignition. They also make a mess - but if the choice is a fire or a mess, take the mess.
There are two kinds of dry chemical extinguishers:
z Type BC fire extinguishers contain sodium or potassium bicarbonate.
z Type ABC fire extinguishers contain ammonium phosphate.
z CO2 (carbon dioxide) extinguishers are designed for class B and C fires. They don’t work very well on class A fires because the material usually reignites.
CO2 extinguishers have an advantage over dry chemical in that they leave behind no harmful residue. That makes carbon dioxide (or other suitable gaseous extinguishant) a good choice for an electrical fire involving a computer or other delicate instrument.
CO2 is considered a bad choice for a flammable metal fires such as Grignard reagents, alkyllithiums and sodium metal because CO2 reacts with these materials. CO2 extinguishers are not approved for class D fires.
Other fire extinguishers:
z Metal/Sand Extinguishers are designed for flammable metals (class D fires) and work by simply smothering the fire. The most common extinguishing agent in this class is sodium chloride, but there are a variety of other options. You should have an approved class D unit if you are working with flammable metals.
If your industrial complex faces the risk of metal fires, the following extinguishants should be considered:
z Sodium chloride (NaCl) works well for metal fires involving magnesium, sodium (spills and in depth), potassium, sodium/potassium alloys, uranium and powdered aluminium. Heat from the fire causes the agent to cake and form a crust that excludes air and dissipates heat.
z Powdered copper metal (Cu metal) is preferred for fires involving lithium and lithium alloys. Developed in conjunction with the U.S. Navy, it is the only known lithium firefighting agent which will cling to a vertical surface thus making it the preferred agent on three dimensional and flowing fires.
z Graphite-based powders are also designed for use on lithium fires. This agent can also be effective on fires involving high-melting metals such as zirconium and titanium.
z Specially-designed sodium bicarbonate-based dry agents can suppress fires with most metal alkyls, pyrophoric liquids which ignite on contact with air, such as triethylaluminum, but do not rely on a standard BC extinguisher for this purpose.
z Sodium carbonate-based dry powders can be used with most Class D fires involving sodium, potassium or sodium/potassium alloys. This agent is recommended where stress corrosion of stainless steel must be kept to an absolute minimum.
A few other extinguishers worth noting include:
z Halotron I extinguishers, like carbon dioxide units, are for use on class B and C fires. Halotron I is an ozone-friendly replacement for Halon 1211 (which was banned by international agreements beginning in 1994).
This ‘clean agent’ discharges as a liquid, has high visibility during discharge, does not cause thermal or static shock, leaves no residue and is non-conducting. These properties make it ideal for computer rooms, clean rooms, telecommunications equipment, and electronics. The superior properties of Halotron come at a higher cost relative to carbon dioxide.
z FE-36TM (Hydrofluorocarbon-236fa or HFC-236fa) is a DuPont-manufactured Halon 1211 replacement that is available commercially in Cleanguard(r) extinguishers. The FE-36 agent is less toxic than both Halon 1211 and Halotron I. In addition, FE-36 has zero ozone-depleting potential; FE-36 is not scheduled for phase-out whereas Halotron I production is slated to cease in 2015. A 100% non-magnetic CleanGuard model is now available.
z Watermist extinguishers are ideal for Class A fires where a potential Class C hazard exists. Unlike an ordinary water extinguisher, the misting nozzle provides safety from electric shock and reduces scattering of burning materials. This is one of the best choices for protection of hospital environments, books, documents and clean room facilities.
In non-magnetic versions, water mist extinguishers are the preferred choice for MRI or NMR facilities or for deployment on mine sweepers.
If you work around extremely high field magnets such as magnetic resonance imaging (MRI) machines or nuclear magnetic resonance spectrometers (NMR’s), you should only have non-magnetic fire extinguishers on hand.
The magnetic field of an MRI or NMR machine is strong enough to make a steel cylinder fly across the room with lethal force.
Do you need to find out more about extinguishers? OSHA has many standards covering fire safety which pertain to extinguishers.
Care and maintenance
At least once a month (more often in severe environments) you should inspect your extinguisher. If the extinguisher is damaged or needs recharging, get it replaced immediately!
One more time: Recharge all extinguishers immediately after use regardless of how much they were used!

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