Date: Tue, 21 Apr 1998 17:03:05 -0700
Reply-To: Björn <bratjen@DIRECT.CA>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: Björn <bratjen@DIRECT.CA>
Subject: fire extinguisher researched (long, firefighting info)
Content-Type: text/plain; charset="iso-8859-1"
Well, let's hear it from a firefighter.
Fire extinguishers have have four classes:
A: wood, paper products, some plastics
B: flammable liquids
C: charged electrical equipment
D: combustible metals
In a vehicle you are concerned mostly with A,B, and D type fires.
Interestingly fire departments use mostly water for extinguishing car fires
unless there is a larger fuel spill (class B, where foam would be used) or
magnesium components such as the transmission housing in a vanagon and type
2 (class D, where special agents or dirt would be used, no water because it
would fuel the fire). A class C fire is reclassified by turning off the
electricity.
How effective the agent is also depends on the amount that is available. A
trickle of water may produce steam but does little else. A typical car fire
extinguisher will be empty after about 20-40 seconds.
Fire needs four things:
fuel, heat, oxygen, chemical chain reaction
If you take one of these components away you will have no fire.
Examples:
Water takes away temperature but has to be available in sufficient
quantities. A CO2 extinguisher takes away oxygen, but is succeptible to wind
influence. A powder extinguisher also interrupts the access to oxygen and
because reignition can occur easily a coating agent is added which makes the
powder stick to hot surface. The powder in an A,B,C type extinguisher is
very corrosive and difficult to remove from cars once applied. That's where
there is additional damage in the long term through rust.
Halon interupts the chemical chain reaction and as a gas is also influenced
by wind and location. Halon however is detrimental to the atmosphere and can
build very toxic components in high heat. That's why it has been mostly
discontinued.
In a car fire the key elements are size of fire and speed of response. It is
really a question of damage control. The small car extinguishers are usually
good to buy some seconds to extricate a person unless you catch the fire
very early.
By the way cars usually do not explode as seen in the movies. There can be
spontaneous combustion through fuel leaking onto hot engine components. But
that happens usually immediately during an accident and produces first small
then rapidly expanding fires. One exception is the Ford Pinto where the fuel
tank could burst upon rear impact on the differential which sprayed fuel
over the exhaust (genius at work). VWs will generally not explode (unless
sufficient heat is applied to propane tanks in campers and even they usually
vent first).
Vanagons mostly have fires through leaks in their array of fuel lines, like
improper connections to the injectors, or through some camping accessories
or electrical causes.
To extinguish a fire:
Think about safety first (passengers, people, traffic, etc., the gases
coming from a burning vehicle can be extremely toxic)
Think about removing the fuel
(i.e. disconnect battery in an electrical fire) and things which can burn (I
once removed a burning hose from the auxiliary heater on a 75 Bus to
extinguish the fire).
Think about limiting the spread of the fire and try to remove oxygen
(i.e. use water, dirt, fire extinguishers, etc. I was at a scene where a guy
successfully extinguished an engine fire in his VW Bug by throwing roadside
dirt into the engine compartment, which meant overcoming some inhibitions)
A note on use of fire extinguishers think PASS:
At the scene
Pull the pin
Aim towards the fire
Squeeze the handle
Sweep spray towards base of fire
My suggestion: prevent fires through maintenance and keep a cool head.
regards,
Björn
