FireNet Community
FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Fire Safety => Topic started by: Tom Sutton on January 30, 2009, 11:30:36 AM
-
I have just become an office fire warden and seen a training DVD, one thing occurred to me was looking at the kinds of fires and extinguishers and their applicability to offices. We have water and CO2 the former useful for Class A and the latter for Electrical.
Given the amount of cabling etc in any office it seems to me that any Class A fire could potentially also be electrical (without it being evident as such) and so to start off with Water and risks electrocution.
Would it not be smarter to use Foam as it would cover Class A and electricals?
Before I respond to the above question does anybody have any views as I have noticed in many premises water extinguishers are being replaced by foam?
-
Needs to be made clear that it is the foam spray extinguishers that may usefully serve a dual role. I have noticed, however, that while such extinguishers may have passed the high-voltage test very few makers/sellers actually state they are usable on office and similar electrical equipment. There is a problem in that the foam discharge will quite quickly form conductive puddles in/round the equipment which may lead to a shock hazard, particularly if the circuits are not protected by RCDs.
RCDs are only required for the protection of sockets in commercial and industrial premises by the latest (17th Edition) of the Wiring Rules (BS 7671:2008) so there will many such premises not fitted with RCDs for some time to come.
-
The 9 litre/2 gallon plain water jet extinguisher dates back over 100 years and has been overtaken by changing technology & work practices.
Up until the 70's & 80's in most premises you would see water's and very few of anything else as the primary risk was always straight Class A.
An increasing use of electrics and electronics and plastics (some molten/liquid when on fire) has changed the dynamics, as has the advent of manual handling regulations and even sexual equality! (Woolworths, Boots and M&s used to install 1 gallon/4.5l/10 pint water extinguishers in double numbers (to meet FOC rules) due to predominantly employing women)
In theory in trained hands a water jet extinguisher shouldn't be a risky prospect even in the modern mixed risk office, but the risks are greater than in the past. Plus you have the weight aspect - up to 14 kilos.
You have available Foam Spray & Water Additive extinguishers, both in 3 & 6 litres and both having 13A from just 3 litres. Thus handling is a lot easier as you only need to lug around 6 kilo instead of 14 kilo, yet don't need to double up in numbers (in the old days a 4.5 or 6 litre water jet was only 8A)
Also virtually all decent makes of Foam Spray & Water Additive extinguisher have passed the 35kV test so as to protect the operator against accidental/inadvertant discharge onto electrical equipment.
Neither are intended or approved (with the odd exception) for direct use on electrical equipment.
It would be sensible to phase out water jets with water additive or foam as replacement becomes necessary, but you will still need CO2 for your special risks (electrical equipment).
-
Further point:
Foam branch pipe extinguishers (still available from a few places) are not 35kV approved.
Bargain imported CE only marked foam spray are not all 35kV tested and do not have the same safeguard - the BSEN3 kitemark is usually a fair sign that the 35kV test has been carried out.
The Amerex Water mist (not spray) extinguisher is rated & labelled for direct electrical use in the US & is marketed as a Halon & CO2 replacement for high value electronics, although Amerex UK haven't followed this through on UK labelling
-
Just imagine the liability issues if they did AB! Although they do have paperwork advertising the water mist as a non magnetic unit suitable for high value NSH specialist electrical kit. If memory serves they are the US model sold over here by Amerex UK but not with any BS authorised label (but I have slept since last providing one..)
Foam Spray 3/6Lt or Water Additive 3Lt would be the best option for safe in an electrical environment - i.e. electrical equipment in the area not specifically for elecrical equipment (that's Co2) e.g. office, light weight and for non trained personnel use - training should be paramount to allow a user to make an informed decision - but this is after all the real world and we all know what that means.....
-
Thanks for all the replies so far, I can see the advantages of less weight combined with an increased rating meaning less units required. I have had no practical experience in using these extinguishers, so how effective are in extinguishing a fire and does spray foam use smothering to extinguish the fire or is there an increase in the cooling effect? I suppose my question is what are the advantages and disadvantages of theses types of extinguishers?
-
The foam spray extinguisher cools a class A fire, the additives are detergent based so they wet the fire more effectively than plain water, hence greater cooling.
One big difference is the throw of the extinguisher. Whilst the water extinguisher often has a throw of 8 m at first- and too much pressure sometines causing excessive disturbance of materials at the base of the fire, the foam spray give a much softer discharge- you have to be within about 2-3 m of the fire.
And dont forget that although the fire rating can be the same the duration of the smaller extinguishers is much lower, this means that in untrained hands when the thing is not being used effectively theres probably less margin fo rerror?
-
Kurnal, I agree, a good result all round. Light, effective and if used not too long a duration for someone to stand there with it.
-
Although you have less range the spray can shield an operator better.
The foam or water additives break the surface tension of the water as described, allowing more effective penetration & hence why the first water additive extinguisher introduced by Nu Swift in the 50's was called 'Wet Water' making 'water wetter'
The spray means you get a quicker flame knock-down as well.
To put the context of the difference in discharge times a 3 litre water additive will have run out after 18 seconds, whereas the traditional 9 litre water can still be going after 45-55 seconds, with another 5-10 seconds of ineffective spurting and hissing thereafter.