The purpose of this page is to provide further information regarding the
provision of Class B cover in accordance with the recommendations of
BS 5306-8:2000. 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.
- The assessment of cover for a single liquid container in a given room is
calculated via the total surface area of the container and the table below1.
This table gives the maximum surface area (in m²) for which a given rated
extinguisher(s) is(are) suitable.
| Individual Extinguisher Rating |
21B |
34B |
55B |
70B |
89B |
113B |
144B |
183B |
233B |
| Max Area for 1 extinguisher (m²) |
0.14 |
0.23 |
0.37 |
0.47 |
0.59 |
0.75 |
0.96 |
1.22 |
1.55 |
| e.g.
Circular area of following diameter (m): |
0.42 |
0.54 |
0.69 |
0.77 |
0.87 |
0.98 |
1.11 |
1.25 |
1.40 |
| e.g.
Rectangular area, 0.5m by following length (m): |
0.28 |
0.46 |
0.74 |
0.94 |
1.18 |
1.50 |
1.92 |
2.44 |
3.10 |
| Max Area for 2 extinguishers (m²) |
0.26 |
0.42 |
0.69 |
0.88 |
1.11 |
1.41 |
1.80 |
2.29 |
2.91 |
| e.g.
Circular area of following diameter (m): |
0.58 |
0.73 |
0.94 |
1.06 |
1.19 |
1.34 |
1.51 |
1.71 |
1.92 |
| e.g.
Rectangular area, 0.5m by following length (m): |
0.52 |
0.84 |
1.38 |
1.76 |
2.22 |
2.82 |
3.60 |
4.58 |
5.82 |
| Max Area for 3 foam only ext's (m²) |
0.42 |
0.68 |
1.10 |
1.40 |
1.78 |
2.26 |
2.88 |
3.66 |
4.66 |
| e.g.
Circular area of following diameter (m): |
0.73 |
0.93 |
1.18 |
1.34 |
1.51 |
1.70 |
1.91 |
2.16 |
2.44 |
| e.g.
Rectangular area, 0.5m by following length (m): |
0.84 |
1.36 |
2.20 |
2.80 |
3.56 |
4.52 |
5.76 |
7.32 |
9.32 |
For example, a room containing a flammable liquid container measuring
1m×0.5m has an area of 1×0.5 = 0.5m² which requires 1×89B, 2×55B, or 3×34B.
Note that if 3 were supplied, they would all have to be foam. Note, this cover
does not include the spillage cover given below.
- In cases where there are multiple containers less than 2m apart, they
should be considered as an undivided container equivalent to a single
container with a surface area equal to the total surface area of the group2.
- In cases where there are multiple containers that are more than 2m and
less than 20m apart, they should be considered as forming a divided group. The
surface area of the largest single container, the total surface area of the
largest undivided group (as above), or one third of the total surface area of
all of the containers, whichever is the greater, is used to calculate the
minimum rating3.
- In cases where the containers are more than 20m apart, the containers
should be considered on an individual basis4.
- Additional extinguishers should also be supplied to cover the hazard from
spillage. The recommended minimum rating = 10×Anticipated Spillage Volume (in
litres)5. Refer to the British Standard
for full details.
- The table above gives minimum cover levels. Additional extinguishers
should be provided where the liquids have a low fire point, or are
particularly difficult to extinguish6.
- Where high rated extinguishers are installed, additional low rated
extinguishers should be provided and sited near any anticipated points of fire
occurrence6.
Unfortunately, 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: Part 8: 2000, clause 6.3.3.1
- As per BS 5306: Part 8: 2000, clause 6.3.3.2
- As per BS 5306: Part 8: 2000, clause 6.3.3.3
- As per BS 5306: Part 8: 2000, clause 6.3.2 b
- As per BS 5306: Part 8: 2000, clause 6.3.3.4
- As per BS 5306: Part 8: 2000, clause 6.3.4
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