Current affairs
which produce a ‘straight jet’; if this was to come into contact with a live conductor. Given that possibility, is there no way we can
try to get back to a safe, universal agent – with the great improvement in training and reduced maintenance costs which a single type of extinguisher might provide?
Agent Water Dry powder CO2
Size A rating
9 litre 21 4kg 27
Watermist
Wet chemical 3 litre 8 2kg X 1 litre X 3 litre 8 6 litre 13
B rating
X
89 55 X X
13 21
F rating
X X
75 X 5
25 75
Comparative ratings and characteristics of portables
fire coverage, albeit with the ‘A’ rating lower than the equivalent size of water extinguisher. I assume that this is consequential of the need for a greater part of the cylinder to contain propellant gas. I wonder whether there might be also be a case
that the tests employed to gauge the A rating are those which were specifically designed for water gas and stored pressure water units. If this is the case, it would be a bit like testing a sprinkler system alongside a watermist system in the floor pan test, and concluding that the sprinkler was superior as there was more water discharged per m2
. However, I believe that the main barrier to wider
acceptance of the mist units is the way in which the present BS guidance document is worded. The wording in the 2012 version of BS 5306 Part 8: Fire extinguishing installations and equipment on premises. Selection and positioning of portable fire extinguishers. Code of practice, is very conservative in its consideration of fires involving live electrical equipment. The standard contains a note reflecting that it is
Watermist extinguisher Watermist
Portables using watermist have been available in the UK for some 15 years, but do not appear to have been promoted as widely as they might have been. Apart from their widespread effectiveness, they have a major advantage: a high level of dielectric safety. All of the units that I have been able to
determine are on the market in the UK claim compliance with a 35kV test, and most appear to claim that the units are ‘safe up to 1000V’. There are a number of reasons why these claims can be made. Firstly, the water is applied as a ‘mist’, not a straight stream, and secondly, the water used is of greater purity without any additives. Examination of the effectiveness of the units in standard tests suggest that they provide full ABC
‘national practice’ not to label extinguishers which have passed the 1000V test as safe for use, but only to mark those extinguishers which have not passed the test as unsuitable. I believe there is a clear case that BSI’s committee FSH/2 – which is responsible for BS 5306 Part 8 – should commission, or BSI itself should undertake tests, to determine whether watermist extinguishers are safe to use in locations where live equipment may be found, but where voltages are very unlikely to exceed 415V. BSI has a substantial business in the testing of
portable fire extinguishers as a commercial activity, and it would seem not unreasonable that such work could be funded by them. A more positive statement within BS 5306 Part 8 would allow wider use of watermist, and greatly assist competent persons in their compliance with Article 13 of the Regulatory Reform (Fire Safety) Order 2005, and S12 duties under the Scottish fire regulations. Clearly, reducing the number of different types of extinguishers will assist greatly in training
Stewart Kidd is a fire and security consultant and chartered security professional. For more information, view page 5
www.frmjournal.com NOVEMBER 2018 51
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Electrically safe?
No Yes No Yes Yes Yes Yes
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