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A dampener on loft living

Care should be taken when extending into roof spaces, but sprinklers could free up the design and prove cost-effective

When home owners are looking to obtain more living space they often consider converting the loft or roof space or adding an additional storey.

A simple solution to the problem but one that, depending on the height of the proposed extension, can attract more stringent fire safety requirements than may already be required for the dwelling.

This is understandable as, in the UK, fire statistics show that most deaths from fire occur in the home.

The most recent statistics show that dwelling fires rose by 1 per cent in 1999, to 72,100, and that 466 people died in fires in the home with 14, 600 injured.

Approved Document B, 'Fire Safety', offers practical guidance on meeting the fire safety requirements of the Building Regulations in England and Wales. It is important to note that the Building Regulations (Parts A to K and N of schedule 1) are only concerned with 'securing a reasonable standard of health and safety for persons in or about the building' which, in the case of fire safety guidance, means ensuring people are able to escape safely from the building.

If property protection is required, then additional measures to that given in the guidance may be necessary.

While compliance with the Building Regulations Approved Document is one way of meeting the standards, fire safety engineering offers an alternative approach to meeting the requirements, or 'for solving a problem with an aspect of the building design which otherwise follows the provisions'.

In the case of private dwellings, because of the size of the building, the opportunities for the application of fire safety engineering are limited - but it should not be ruled out.

Certainly, where the prescriptive requirements cannot be met, fire safety engineering can provide an alternative, and the use of mathematical modelling, computational fluid dynamics and evacuation modelling can show that a proposed system will allow people to escape from a building safely and within a reasonable time.

The requirements for dwellings are onerous and can add considerable expense to a project, particularly where alternative means of escape are concerned. (Against this, it should be remembered that 70-80 per cent of all fire deaths and injuries occur in the home. ) An important tool in the reduction of fire casualties has been the installation of automatic early warning systems, such as smoke detectors.

As of July 2000, Regulation B1 required that suitable arrangements be made to give all buildings early warning systems. To meet this requirement, houses and dwellings need to have a suitable number of mains-operated smoke alarms (domestic battery-operated detectors are not be suitable). The 'suitable number' is dependent on the size and design of the dwelling and the standard of the system to be installed. At the very least, the regulations require installation of detectors in circulation spaces. Loft conversions are specifically mentioned in this section.

Where a loft in a one- or two-storey house is converted into habitable accommodation, an automatic smoke detection and alarm system, based on linked smoke alarms, will need to be installed.

A habitable room is defined as 'a room used, or intended to be used, for dwelling purposes' (including for the purposes of Part B a kitchen, but not a bathroom). The key phrase is 'intended to be used', so conservatories, utility rooms and storage areas, which obviously have the potential to be used as 'habitable rooms', can also fall within this definition and cannot be excluded from the requirements for means of escape.

As a rule of thumb, if it's not a bathroom and it is big enough to stand up and lie down in, it will be categorised as a habitable room.

In general, the higher the storey, the more difficult it is to escape. So the regulations concerning means of escape from houses are based upon the height of the building, with various provisions dependent upon the number of floors and height above ground level.

Houses with only one staircase, and that have floors not more than 4.5m above ground level, should have an emergency egress window (or external door) at that storey height.

Dormer or roof windows are acceptable as escape windows, but the base of the window should be no more than 1,700mm from the eaves.

One window may serve two rooms, but there must be access to that window through a communicating door, without having to pass through the staircase enclosure. If an emergency egress window is used, then the person using it must be able to escape so they are clear from danger from fire. If escape is into an enclosed yard or garden where exit is possible only through other buildings, then the depth of the yard or garden needs to be at least the height of the midpoint of the roof above ground level.

Where a house has one floor 4.5m above ground level there are three possible solutions.

The first is to have an additional internal stairway that provides an alternative means of escape.

The second is for the upper storeys to be provided with a protected staircase which extends to a final exit, or gives access to at least two different escape routes separated by fire-resisting construction and selfclosing fire doors.

The third option is for the top storey to be separated from the lower storeys by fire resisting construction and to be provided with an alternative escape route that leads to its own exit.

Where a house has more than one floor 4.5m above ground level, then as well as meeting the provisions in the second stage an alternative escape route must be provided for each storey 7.5m or more above ground level. At or around 7.5m, the protected stairway may need to be separated from the floors below by fire-resisting construction, depending on where the escape access is.

There is no obligation for the provisions of the Approved Document to be followed, but the architect or designer will need to show that the functional requirements of the regulations are satisfied.

One alternative is to follow the British Standard 5588 codes of practice, Fire Precautions in the design construction and use of buildings;

Part 1 being the code for residential buildings. If this approach is followed, then generally all the recommendations should be followed as all the measures within the code are intended to support one another. A mix-and-match approach between standards may not necessarily achieve a satisfactory solution for safety.

Notwithstanding the need to satisfy statutory regulations, a fire engineered approach can be deemed appropriate and, in many instances, can provide a more flexible response in design terms.

Computer fluid dynamics, fire modelling and evacuation modelling can be used to demonstrate to a building control officer's satisfaction that alternative solutions work. Fire models are collections of procedures that build upon a series of individual calculations and core routines used to evaluate the complex, interactive process of fire hazard analysis. They are generally intended for use only by those competent in the field of fire safety and are intended only to supplement the informed judgement of the qualified user.

The software is intended to provide quantitative estimates of some of the likely consequences of a fire, and the underlying models will have been subjected to a range of verification tests to assess the accuracy of the calculations. Like any computer calculation, however, the results are directly related to the quality of the inputs provided by the user.

The software may or may not have a predictive value when applied to a specific set of factual circumstances.

Inappropriate use could lead to erroneous conclusions.All results need to be evaluated by an informed user.

By using fire models it is possible to chart, against time, the height and temperature of the smoke layer and the heat release rate plus the levels of carbon monoxide in the room of origin and other areas to which the fire may spread.

The objective of using computerbased mathematical models is to simulate human evacuation of the premises, and to see if the building design could promote quick and easy evacuation in the event of a fire or an emergency situation (see 'Escaping preconceptions', AJ 25.1.01).

The evacuation modelling programme attempts to replicate human behaviour and movement by imposing 'rule-based' behavioural characteristics onto the population of the building. Therefore, the model follows a number of rules which recognise the behavioural traits of individuals.

One fire engineered solution that may be acceptable to the building control and fire authority is the installation of a domestic sprinkler system. This need not mean large arrays of pipework, huge storage tanks and control systems, ugly sprinkler heads and big bills for installation and maintenance. A domestic sprinkler system typically comprises a water supply, stop valve, priority demand valve, automatic alarm system (internal and external) and pipework to quick response sprinklers.

The sprinkler heads will operate at a pre-determined temperature, discharging water over a known area beneath, with the water flow initiating the sounding of an alarm. Only those heads responding to a direct heat source will be activated. It need not be that expensive, but the benefits are huge.

In the US, Canada and Australia, domestic sprinkler systems have been installed for many years and have saved life and property.

In Scotsdale, Arizona, for example, a comprehensive community sprinkler ordnance requires mandatory sprinkler installation in new homes.

Passed in June 1985, it has resulted in a per capita fire loss that is less than one-quarter the national average.

Also, despite a 60 per cent population growth, Scotsdale has managed to lower its fire loss by 84 per cent.

A Loss Prevention Council technical bulletin, Sprinkler Systems for Dwelling Houses, was published more than 10 years ago, but due to a number of flaws in the guide it was difficult and expensive to implement. This has now been redressed with the publication of DD 251:2000, the Code of Practice for Sprinkler Systems for Residential and Domestic Occupancies, which is based upon the American NFPA 13D standard. Extensive application of this standard to domestic property has the potential to make a huge impact on safety in dwellings.

Despite the Building Regulations and the advent of domestic smoke detection, fire deaths in the home are still high.

Without sprnklers, loft conversions will normally require one or two fire doors which often look intrusive.

The other problem with fire compartmentation is that people need to get from one side of it to the other, necessitating breaches in the barrier.

Doors tend to get wedged open, rendering compartmentation useless. (How many young children go to sleep with their door open at night? ) Smoke detection has made a huge impact on domestic fire safety, but battery-operated detectors are only reliable if the batteries are working.

The new requirement for mainsoperated detection systems should contribute to further reductions in fatalities in fires, but fire detection systems only give warning of fire, they do not control or extinguish it, and it is the speed with which fire and smoke can spread that causes a number of domestic fire deaths.

Domestic sprinkler systems can supplement the detection systems by detecting and controlling or extinguishing the fire at an early stage and activating an alarm. The system can rapidly reduce the rate of production of heat and smoke so that additional time is available for the building occupants to escape or to be rescued.

They can also prevent 'flashover' in the room where the fire starts, a phenomena which causes extensive fire spread and has led to a number of deaths.

It is for these reasons that domestic sprinklers, installed to the correct standard, can form a part of a fire engineered solution which meets with the functional requirements of the Building Regulations.

Kevin Thorpe is a senior fire engineer with fire consultant Lawrence Webster Forrest. Tel 020 8655 1605, or e-mail: fire@lwf.co.uk

SPRINKLERS - THE FACTS

Domestic sprinkler pipes and fittings can use plastic or other pipes, typically of 22mm diameter, with pipe runs similar to central heating systems.

Mains supply usually gives adequate pressures to obviate the need for water storage.

Sprinkler heads can be fitted with ceiling rosettes and painted to match any colour scheme. Spacing is such that only one or two heads may be required per room. Concealed heads, which are recessed and covered by flat plates, may be acceptable.

On average only one or two heads will operate and control or extinguish the fire until the Fire Brigade arrives. Accidental discharges are rare and less likely than a burst water pipe.

In Scotsdale, Arizona, the estimated amount of water discharged when a residential sprinkler activated was 940 litres compared with an estimated 16,600 litres used by firefighters to extinguish a house fire.

On average, the cost of a domestic sprinkler system is equivalent to carpeting a house or installing a central heating system.

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