Mist Fire Protection Sprinkler Systems - By Stuart Kidd


Having been in use for more than 30 years, the one thing that's safe to say about fire sprinkler systems is that they are tried and tested. They are also entirely predictable – which in the instance of something as devastating as fire is an entirely good thing.

However, like everything in life, there are some disadvantages to sprinklers. They involve a high demand for water, and generally need large storage tanks and relatively large pipes for distribution. Then there's the age-old assumption that, while their life-saving potential is proven beyond doubt, the post-fire water damage cause by sprinklers will be a major headache.

So, over the past 20 years, an alternative has been developed that ticks some of the boxes not filled by sprinklers: namely, the mist system. The theory behind a mist system is that smaller droplets are better able to absorb the heat produced from a fire, and cooling a fire is often the most effective way of extinguishing it. Also, smaller water droplets turn more easily into steam, which smothers the fire by reducing the amount of air available for it to burn.

Mist systems were first used on boats, where water storage space was at a premium, but over recent years the systems have been fitted in a wide range of locations on dry land, from private homes to schools, hospitals and hotels.

The main advantages are that they use a lot less water – so there's not the same need for water tanks as a sprinkler system – and, therefore, potentially offer lower post-fire water-damage costs. Also, because they require smaller pipes and tanks, they can be fitted into places that are simply too small for sprinklers, such as retrofit properties and heritage sites.

A mist system is made up of the same three main parts as a sprinkler system: a water supply, an alarm system and a distribution system, and they fall into two main categories: low pressure and high pressure. A low-pressure system uses less water than a sprinkler but more than a high-pressure option, involves less maintenance and can share a water supply with an existing sprinkler system. A high-pressure option involves a lot less water storage and smaller pipework, but the system is independent of sprinkler installations or intervention from the fire department.

The key thing, however, is that because mist systems are still relatively new to the market, all the benefits need to be weighed up alongside careful consideration of the performance and reliability of each individual product.

In response to the increased use of mist systems, the fire industry has produced a list of guidelines for installation. But there are still lots of grey areas in the understanding of the products, as Stewart Kidd, Secretary General of British Automatic Fire Sprinkler Association Ltd explains,

'There are still concerns surrounding the way mist behaves. For example, in some instances it behaves more like a gas than a liquid, and can be affected by air movement and the size and character of a building. We have generic tests to support the use of mist systems in some locations, such as private homes and care homes, but in larger locations such as shopping centre's and theatres there are currently no such tests.'

'Each mist system is different, with individual components designed for each installation, so you can't be guaranteed how it will perform.'

But with more companies offering mist systems than ever before, testing and quality control within the industry is also on the increase. BAFSA has recently set up the BAFSA Mist Group, with an independent chairman to work closely with the Fire Industry Association's Water Mist group. The aim is to represent the interests of the manufactures and installers, and to ensure a consistent message to all potential customers about both the advantages and concerns of the systems. To clear the mist, you could say.

BAFSA has produced a checklist of questions to ask before installing a mist system:
• Has the system been tested and approved by a third party body like LPCB, VdS or FM?
• Has all the testing been carried about by a capable laboratory?
• Are the products used in the system approved for such use?
• Can all the claims made by the system be verified?
• Is there a fixed agreement between manufacturer and installer, and has the installer received training from the manufacturer?

If in doubt, the first thing to ensure is that the design and installation of your potential new mist system is being carried out in accordance with DD 8458, which will be published in full by the end of 2010. And if you have any concerns, contact BAFSA for advice at info@bafsa.org.uk

Stewart Kidd BAFSA