Page 115 - International safety guide for oil tankers and terminals

FIRE-FIGHTING

5.2.4 Class D – Combustible Metal Fires
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Class D fires involve combustible metals such as magnesium, titanium,
potassium and sodium. These metals burn at high temperatures and react
violently with water, air and/or other chemicals. Fire extinguishers for use on
Class D fires do not have a multi-purpose rating and must match the type of
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metal involved. Extinguishers rated for Class D fires have a label listing the
metals that the extinguisher can be used on.

5.3 Extinguishing Agents

Extinguishing agents act by heat removal (cooling), by smothering (oxygen exclusion) or
by flame inhibition (interfering chemically with the combustion process).

5.3.1 Cooling Agents

5.3.1.1 Water

The direct application of a water jet onto a fire is an effective fire-fighting
method for Class A fires only. A wetting agent added to water may reduce
the amount of water needed to extinguish fires in tightly packed Class A
materials as it increases the effective penetration of water by lowering its
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surface tension.

For fires involving hydrocarbon liquids, water is used primarily to minimise
escalation of a fire by cooling exposed surfaces. Water spray and water
fog may be used for making a heat screen between the fire and
fire-fighting personnel and equipment. If foam is not available, a water
mist can be used to extinguish fires involving shallow pools of heavy oil.

Water in any form should not be applied to fires involving hot cooking oil
or fat since it may cause the fire to spread.

Concentrated water streams should not be directed at fires involving
liquefied gas as this will increase the hazard by increasing vapour cloud
size as more cargo liquid is vaporised. However, water spray or water fog
can be used on liquefied gas fires and spills. It will cool the area and
control fire intensity as well as enhance vapour cloud dispersion.

Water jets should not be directed at energised electrical equipment as
this could provide a path for electricity from the equipment with
consequent danger of electric shock to fire-fighting personnel.

5.3.1.2 Foam
Foam has a limited heat absorbing effect and should not normally be
used for cooling.

5.3.2 Smothering Agents

5.3.2.1 Foam
The primary extinguishing action of foam is by smothering. Foam is an
aggregation of small bubbles, of lower specific gravity than oil or water,
which flows across the surface of a burning liquid and forms a coherent
smothering blanket. A good foam blanket seals against flammable vapour

© ICS/OCIMF/IAPH 2006 81