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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 only.

Throughout, references to the pertinent parts of the British Standards and/or other legislation have been included as footnotes.

Class C Cover – Gaseous Hazards

Class C extinguishers should be provided to cover any class C hazards^{1, 2}.

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 fire^{2, 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, 7}.

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 alloys:

• iron

• (non-stainless) steel

• copper

• aluminium

• titanium; and

• zinc

Such swarfs and powders will be very common in metal working premises and thus need protecting with a class D extinguisher accordingly.

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 assessment.

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.

Full Copies of Standards

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.

1. As per BS 5306-8:2012, clause 7.1.
2. As per BS 5306-8:2012, clause 8.4.2.
3. The superseded version of this standard, BS 5306-8:2000, clause 6.5.1.
4. As per BS 5306-8:2012, clause 6.4.
5. As per BS 5306-8:2012, clause 8.4.1.
6. As per BS 5306-8:2012, clause 4.5.
7. As per BS 5306-8:2012, clause 8.5.1.
8. As per BS 5306-8:2012, clause 8.5.2.