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Recent history has seen problems in many areas of the country with water supplies due to drought conditions. The problem no longer seems an isolated event and global warming appears to indicate that drought conditions will be an annual occurrence in many regions of the country.
The water regulator, OFWAT, has demanded that the privatised water companies reduce losses due to leakage. The water companies have as a consequence reduced water pressures in mains supplies to achieve this.
Sprinkler systems rely on water from the town's mains. Some Systems are fed directly from the towns main and it is these systems to which this article is targeted.
Systems with pump and tank installations are generally less affected by reductions in towns main supply pressures as the towns main is generally used to keep the tank topped up.
There is no legal minimum pressure which water companies must supply. It has been suggested that pressure will not fall below 1/1.5 bar. This, however, is inadequate for most systems and therefore seriously affects the systems ability to control a fire. The problem is further compounded in that mains pressure in your area may be reduced without your knowledge. In other circumstances, water companies may alert customers where major work is proposed that will interrupt supplies but this approach is not uniform.
Sprinkler systems are designed to meet the potential fire hazard within a building, which varies dependant on the amount and type of goods stored or the type of hazardous manufacturing processes involved. For example, a non hazardous manufacturing risk with low level storage (typically less than 3 metres high) in a 7 metre high building will require 1,100 and 1,350 litres/minute at a minimum pressure of 2.4 and 2.1 bars respectively.
Where pressures or flows are reduced below this threshold the sprinkler system may be overwhelmed.
The Rules for Automatic Sprinkler Installation
BSEN12845 and the accompanying technical bulletins advise that weekly tests of the sprinkler alarm bell and 6 monthly tests of the water supplies be carried out and results recorded. These results will show where there has been a significant drop in pressure or flows available.
Where maintenance is undertaken by a sprinkler contractor they may have already established that there has been a drop in pressure in the area. Their contract is normally to test supplies twice yearly. Their experience in the vicinity may alert them to the issue of general reduction in water pressure.
The first step should be to contact the local water company to ascertain if work is being carried out locally which would reduce pressures. Their answer would indicate if the problem can be resolved, or if this is likely to be a permanent change. Where the situation becomes permanent, more drastic action may be necessary to ensure the system operates effectively. This may include provision of pump(s) and a tank. The specification for these will depend on the nature of the risk. Where a new installation of sprinklers is being considered, it may well be worthwhile to install pump(s) and tank at the outset as this would negate any problems in supplies in the future.
Key Action Steps
BSEN12845 - Fixed fire fighting systems- Automatic sprinkler systems- Design, installation and maintenance.
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