The purpose of this page is to provide further information regarding the
provision of cover for class C and class D fire hazards in accordance with the recommendations of
BS 5306-8:2012. Readers are referred to
the British Standard itself for full details and reminded that this is a summary
Throughout, references to the pertinent parts of the British Standards and/or
other legislation have been included as
Class C Cover – Gaseous Hazards
Class C extinguishers should be provided to cover any class C hazards1,
Due to the specialist nature of class C fires, this British Standard
gives little guidance on the number of extinguishers required for any
given class C hazard other than with reference to "detailed
fire risk assessment and a health and safety risk assessment"2.
However, the previous version of this British Standard advised that "The
size of extinguisher is not critical as even the smallest can extinguish
a 7 mm leak in a high-pressure gas line. In these circumstances the
flame might be some 13 m long"3.
Accordingly, for class C hazards, we typically recommend at least one 2kg powder
extinguisher to comply with this standard, with any increased
requirements as per the detailed
fire risk assessment
and health and safety risk assessment2.
Class C extinguishers should be sited such that there is not necessary
to travel further than 30m to the site of any potential class F fire4. These travel distances should be
reduced if there are doorways on this route4.
Specialist staff training is critical for any person to extinguish
a class C fire2, 5, 6. Gas leaks should
typically be extinguished by closing a control valve or plugging the leak5. Extinguishing it by any
other means can potentially substantially increase the risk and
introduce an explosion hazard5.
Class D Cover – Hot Metal Hazards
Class D fires are any involving metals and BS
5306-8 requires that “For fires of combustible metals, specially
formulated class D powder types of extinguisher should be used”1,
Whilst one may think of metals such as magnesium in
this context, it’s important to remember that this can also include
swarfs and/or powders (even though larger volumes will not be flammable
in most circumstances) of the following more everyday metals and their
Such swarfs and powders will be very common in
metal working premises and thus need protecting with a class D
However, it is not possible to make general recommendations for the provision of
extinguishers to protect against combustible metals (e.g. magnesium). Decisions
should be made solely by experts on a case-by-case basis8. The use of
inappropriate equipment can make a situation far worse7.
Any class D hazards should be carefully risk assessed8,
including as part of a fire risk
There are no specific maximum distances prescribed in
BS 5306-8:2012, instead stating that such maximums
should be determined by experts on a case-by-case basis8.
However, the recommendations re travel distance set out in the
points applicable in
all cases points applicable in all cases section still apply.
For reference, other
flammable metals include (but are not limited to): calcium, cerium,
cesium, lithium, lutetium, magnesium and magnesium alloys, neodymium,
phosphorus, potassium, potassium-sodium alloys, rubidium, sodium,
strontium, aluminum (powder), beryllium (powder), nickel catalyst
(Raney), titanium (powder), zinc (powder), zirconium (powder), aluminum
phosphide, calcium carbide, gallium arsenide, gallium phosphide, lithium
aluminum deuteride, lithium aluminum hydride, lithium aluminum hydride
bis(tetrahydrofuran), lithium amide, lithium borohydride, lithium-6
deuteride, lithium hydride, lithium tetraphenylborate
tris(1,2-dimethoxyethane), lithium tri-tert-butoxyaluminohydride,
magnesium hydride, phosphorus pentasulfide, potassium hydride, Red-Al,
sodium aluminum hydride, sodium bis(2-methoxyethoxy)aluminum hydride in
toluene, sodium borohydride, sodium borohydride cobalt-doped, sodium
borohydride on alumina, sodium hydride, zinc phosphide.
The British Standards are covered by copyright and are not available freely. However, these can be purchased at
British Standard Online or alternatively, some libraries may carry copies of
the more common standards.
- As per BS 5306-8:2012, clause 7.1.
- As per BS 5306-8:2012, clause 8.4.2.
- The superseded version of this standard, BS 5306-8:2000, clause
- As per BS 5306-8:2012, clause 6.4.
- As per BS 5306-8:2012, clause 8.4.1.
- As per BS 5306-8:2012, clause 4.5.
- As per BS 5306-8:2012, clause 8.5.1.
- As per BS 5306-8:2012, clause 8.5.2.