Date:         Tue, 30 Apr 1996 08:44:09 -0700
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Mark Howser <mchowser@initco.net>
Subject:      RE: Clean Fire Extinguishers

Ken,

Unfortunately, you won't find a fire extinguisher that effectively stops =
the fire and remains clean at the same time.  Fire is the result of a =
chain reaction involving an increase in temperature, availability of =
fuel and an adequate supply  of oxygen for combustion purposes.

To extiguish a fire, interrupt the essential elements of fire.  Doing =
one of these will extinguish the flame.

1. Reduce the temp.
2. Remove the fuel.
3. Exclude O2.
4. Stop the Unihibited Chain Reaction  (Note:  This method is effective =
on gas      =20
    and liquid fuels b/c they must flame to burn.  This is where your =
Halon fire         extiguisher comes in. The Halon (hologenated =
hydrocarbon) replaces the O2 which causes the fire to stop flaming.  =
However,  smoldering fires are not easily extinguished, b/c the moment =
the Halon is shut off, air again has access to the smoldering fuel and =
reignites, continuing to burn.

Types of Extinguishers:

Class A:  Ordinary Combustibles (wood, paper, rubber, plastic)
Class B:  Flammable Liquids (liquids, greases, gases)
Class C:  Electrical Equipment  (live electrical equipment)
Class D:  Combustible Metals (magnesium, titanium, and other "iums")

Class A exting. are rated from 1A to 40A depending on their size.  For a =
1A rating 1 1/4 gallons of water are required.  A 2A rating requires 2 =
1/2 gallons of water. (see the trend?)

A dry chemical extiguisher with a rating of 10A is equivalent to five 2 =
1/2 gallon water extinguishers.

Class B extinguishers are rated from 1B to 640B.  A complicated UL =
rating system best described by  "...the 60B extiguisher will =
effectively extinguish a sixty square foot fire when used by a non =
expert...."

Class C refers to whether the extiguishing agent conducts electricity.  =
You wouldn't want to spray a flaming engine with a class A fire =
extinguisher unless you wanted to chance shock or electrocution.

Class D--you aren't going to effectively stop the spread of burning =
metals with any portable extinguisher.  Call the FD, EPA and any other =
toxic spill agency that comes to mind.

A fire extinguisher is rated as follows.

4A 20B:C

This extinguisher should extinguish a Class A fire that is four times =
larger than a class 1A fire, extinguish approx. 20 sq/ft of class B fire =
and is also safe to use on energized equipment.

Good luck,

Mark
80 Westy
East Glacier Volunteer Fire Department