FPASA BULLETIN FP 01
PORTABLE FIRE EXTINGUISHERS
Most fires, if detected early enough, can be easily extinguished through the prompt
application of the correct type and appropriate quantity of extinguishing agent.
Portable fire extinguishers are designed to fulfil this purpose provided they contain
the most suitable extinguishing agent for the risk being protected.
There are several factors concerning portable fire extinguishers which, if
implemented during pre-planning, will give the user every chance of successfully
extinguishing a fire during those first few minutes.
Factors affecting your choice
The following factors need to be considered to ensure that the correct extinguisher
is selected.

The type of combustible material on site. Some extinguishers can be used
on a variety of combustible materials, but they may have a limited suitability on
specific materials. Reference to suitability appears later in this bulletin.

The possible size of a fire. Some extinguishers while effective on contained
flammable liquids fires, are not capable of dealing with the same amount of
liquid if it is spilt over a large area.

Physical abilities of the operator. Carbon dioxide extinguishers can have a
mass of up to 34 kg for only 12 kg of content and would therefore be far too
heavy and cumbersome for use by most people especially women. It would be
preferable to install several smaller units in these circumstances.

The environment of the extinguisher. Extreme temperatures or excessive
vibration may be detrimental to some extinguishers.

Maintenance requirements. In outlying areas empty extinguishers may have
to be sent away for long periods to be recharged.

Standardisation. It would be wise to standardise on extinguishers which, even
though differing in their content, would operate in the same manner. This would
have distinct advantages in the training of staff who may not be able to regularly
attend instruction sessions or practical drills.
Classification of fires
The selection of extinguishing media for any risk is further simplified by classifying
fires according to type.
Fires involving combustible materials that require the same extinguishing media are
grouped together and are defined in the South African Bureau of Standards Code
of Practice 0105 titled “Code of Practice for the Classification, Use and
Maintenance of Portable Fire Extinguishers”.
The classes are:
Class A
Fires involving ordinary solid combustible materials, eg: coal, paper, plastics, wood
and textiles
Class B
Fires involving flammable liquids and gases eg: alcohols, benzene, oils, paraffin,
petrol, LPG, hydrogen, acetylene.
Class C
Fires of Class A, B or D type occurring in the presence of live electrical installation,
eg: electrical cables, generators, transformers, switchboards.
Class D
Fires involving metals eg: aluminium, magnesium, sodium, potassium and lithium.
Extinguishing media
The design of the extinguisher itself may affect its extinguishing capabilities, but the
selection of the correct extinguisher is determined by the extinguishing agent. The
following is a brief summary of the advantages and limitations of the extinguish
media commonly used in portable extinguishers.
Extinguishing Agent
Water
Has better cooling properties than any other
agent and is therefore best used on Class A
fires.
Class A fires can re-ignite if not
adequately cooled.
Water will also penetrate readily to reach deepseated fires.
Dry powder
Dry powder is generally the best extinguishing
medium for use on Class B fires.
Extinguishers containing dry powders are
capable of dealing with burning flammable
liquids, spread over large areas, more effectively
than other extinguishers of comparable size.
They are effective on fires involving free-flowing
liquids, eg: spillages over vertical surfaces.
Since dry powder is a non-conductor of
electricity it is safe to use on Class C fires.
Foams
Foam extinguishes Class B fires by forming a
blanket of bubbles on the surface of the liquid
and therefore has a smothering effect on the
fires.
Foam extinguishers are best suited for dealing
with small contained flammable liquid fires or for
fires which have been burning for some time
causing the contained to become very hot and
increasing the chances of re-ignition.
Carbon dioxide
Carbon dioxide extinguishers are suitable for
dealing with small Class B fires, whether
spillages or contained. CO2 gas is a nonconductor of electricity and is therefore one of
the safest media to use on live electrical
equipment.
The gas will not contaminate foodstuffs or cause
a mess and because it is emitted as a gas, will
not cause unnecessary damage through fierce
impact as in the case of solid material eg: dry
powder.
Limitations
Water is a conductor of electricity and can be
highly dangerous if used on Class C fires, ie:
fires in the vicinity of live electrical current.
Will cause Class B fires to fare up and spread
and if used on Class D fires may cause violent
explosions
Dry powder has no cooling properties and will
therefore not prevent re-ignition*.
For this
reason it is not as effective as foam on
contained flammable liquid fires which have
been burning for a long time.
Generally powders are messy and some form
sticky deposits on surfaces and must be scraped
and washed away after the fire. These deposits
can have a detrimental effect on delicate
machinery and equipment.
* Re-ignition of Class A fires is prevented by
using multi-purpose (ABC) powders.
Most foams have to form a blanket to extinguish
the fire, and since it is not possible to cover
flowing flammable liquids, foams are not very
effective.
Foam is water based and therefore a conductor
of electricity. It is dangerous to use it on live
electrical equipment. Some foams tend to break
down when in contact with liquids such as
alcohols, and this can prevent the production of
an effective blanket.
The cooling properties of CO2 gas are limited
and it therefore provides very little protection
against re-ignition. Since CO2 is a gas, drafty or
windy conditions will affect its performance.
The effective range of a CO2 extinguisher is also
limited.
Direct impingement of CO2 onto
delicate electrical or electronic equipment could
cause additional damage through cold shock.
Under dry conditions, the discharge of CO 2
extinguishers generates static electricity which
can be uncomfortable to the user.
Suitability
The following table provides a guide to the effectiveness of various extinguishing
agents on different classes of fire.
Type of Extinguisher
Water
Dry powders
Sodium Bicarbonate
Potassium Bicarbonate
Urea Potassium Bicarbonate
Potassium Chloride
Monoammonium Phosphate
Potassium Sulphate
Ternary Eutectic Chlorides
Carbon Dioxide
Foam
Protein
Fluoroprotein
Fluorochemical – AFFF
Synthetic
Key:
Classes of fire
A
B
C
MS D
D
D
D
U
U
U
U
S
U
U
U
MS
MS
MS
MS
S
MS
U
S
S
S
S
S
S
S
U
MS
U
U
U
U
LS
U
MS
D
U
U
S
U
S
MS
Ms
S
D
D
D
D
D
D
D
D
MS - Most suitable
LS - Limited suitability
D - Dangerous
S - Suitable
U - Unsuitable
It should be noted that the suitability of the extinguishing agents as listed above
refers to its use in extinguishers only. Large scale application of foams and CO 2
through specialised equipment for example, may provide very different results.
Published by:
Fire Protection Association of Southern Africa
(Incorporated Association not for Gain)
(Reg.No. 73/00022/08)
P O Box 15467
Impala Park
1472