Lawrence Webster Forrest
Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583
Lawrence Webster Forrest
Tel: +44 (0)20 8668 8663 Fax: +44 (0)20 8668 8583
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In a pioneering introduction to performance-based fire engineering in Madrid, Spain, Lawrence Webster Forrest (LWF) developed a solution for an indoor skiing facility that threw away the text book to create a solution from first principles.
In this bulletin we explain why hospital fire safety needs its own separate code. It also details the major differences in hospital design compared to structures that fall under the scope of Approved Document B, or the BS 5588 series.
Passive fire protection has traditionally been the first line of defence for life safety in buildings. Such measures typically include compartmentation, as well as selecting building materials and methods that will reduce the size and spread of the fire. Buildings are also designed to allow people to escape in the event of an emergency.
Fires have sufficient power to force smoke through the small gaps around doors into protected areas such as stairs and lobbies. But this movement of smoke can be controlled by mechanically altering the forces that cause it. The principles of this method are: * airflow can control smoke movement if its average velocity is high enough * a pressure difference across a barrier can control the movement of smoke These principles are linked, but in engineering terms it is easier to consider them separately. We use velocity in the case of large gaps (open doors) and pressure differences when looking at gaps around closed doors.
Smoke is The airborne solid and liquid particles and gases evolved when a material undergoes pyrolysis or combustion together with the quantity of air that is entrained or otherwise mixed into the mass. (NFPA, 1993). Smoke is the undesirable product that causes the majority of fatalities from fire. In 1999, the most recent year for which detailed figures are available, 238 people died because of smoke and/or gas inhalation, 38% of all deaths (DTLR statistics). With a few exceptions, fires produce a particulate smoke, the effect of which is a reduction in visibility. This in turn will lead to an increase in the time needed to escape, and so also the length of time that occupants are exposed to the products of combustion. Smoke by its nature contains a mixture of substances that can harm an escaping individual. Death will inevitably result if the person does not reach a place of safety before being overcome. For these reasons the control of this toxic substance is best addressed at the design stage.
Fire law in the UK has traditionally been introduced in a piecemeal fashion, mainly as a reaction to a disastrous fire or series of fires. The Fire Precautions Act 1971, for example followed a number of fires in hotels. Such legislation attempts to cover every aspect of fire safety on a national level. Local authorities have been given powers, such as in the Local Government Act 1972 to introduce Local Building Acts (LBA's). These generally address specific risks and form the basis of bespoke fire safety legislation. Buildings that fall under the scope of local building acts may be affected by the following design considerations: compartment sizes automatic fire detection access and facilities for the fire service smoke venting requirements One very significant piece of local legislation is the London Building (amendment) Act 1939, as amended by the Building (Inner London) Regulations 1985. The London Building Act was enforced to deal with the specific risk of high-rise buildings or those covering a large floor area. Section 20 of this Act places more onerous requirements for a number of fire safety issues than those stipulated in the Building Regulations, namely Approved Document B. This issue contains detailed examples of the differences between the requirements of London Building Acts and national guidance. It then goes on to outline the appeals procedure, which can be used if local authority demands are felt to be excessive. Other issues covered include: the importance of geographical location approved inspectors the future possiblity of reform in local legislation. The bulletin emphasises the importance of identifying applicable legislation at an early stage: 'Having to adhere to the requirements of a local building act retrospectively could be time consuming, costly and impractical.'
A fire strategy in conjunction with scale drawings, should unambiguously detail the type of fire safety facilities that are to be incorporated within the building, along with their respective specifications. The method of operation of any system (ie cause and effect), whether active or passive, should also be clearly stated within the strategy. All buildings are different, although the individual types of buildings will fall into certain categories. The categories obviously vary but could include; industrial type buildings, which may lead to high bay storage and abnormal fire loads or manufacturing/processing risks; healthcare or hospital establishments, leading to risks associated with human incapacitation and the implications associated with horizontal escape; or office shop, public or commercial premises, which may lead to risks associated with high population densities or building unfamiliarity. The list quoted is not exhaustive but provides a general slant on the risks associated with more common day to day buildings. It is also worth noting that in reality, lots of buildings will incorporate different categories of risk: e.g. office area included within storage or healthcare premises. Therefore, it is possible that whilst trying to achieve common fire strategy objectives in the preparation of any fire strategy, the approach may have to vary considerably depending upon use and type of the building.
Buildings have had to incorporate for the disabled since the 1970's. The Chronically Sick and Disabled Persons Act was enacted in 1970 and amended in 1976, stating that where members of the public have access to the area it should, where practical and reasonable be accessible to the disabled. It was further detailed as Part M within the Building Regulations in 1985. Part M was amended in 1987, 1992 and again to its current form in 1999, which now describes disabled access to dwellings as well as public premises.
As with many things in life, British Standard 5839, part 1 1988 has grown old and out-dated. In the years that have passed since the last revision of the fire alarm standard, the general technology, fire alarm installation customs and practice have improved and evolved such that the 1988 standard now does not fully cover these new improvements in alarm and detection tecnology. As the document no longer reflects a number of changes in technology, practice and installation procedures the decision has been made to revise the document. So once the decision to revise a British Standard has been made a draft document is prepared and once approved by the code committe is then released to the public as a draft for comment. The closing date for comments was the end of Sept 01 and if as has been the case on previous drafts of various standards and codes, many hundreds of comments have been made. This bulletin has been written outlining the main changes within the draft 5839. Of course these changes may be removed or altered in some format once the final document is issued, but it is believed that the majority of the document will remain largely unchanged. A new bulletin will be written once the final issue of BS 5839 is released.
High rise buildings are an accepted, though often controversial part of any modern city. Within metropolitan areas, land on which to build is often at a premium, especially within business districts and accordingly command a high price. The alternative of building outwards instead of upwards would not give the maximum benefits to owners and developers of commercial land space and would effect both business and economy through increased costs. The other option of building downwards is not viable with regard to large occupanies, costs would be much higher and in terms of fire safety the problem of subterranean fires and upward evacuation are well known and probabilistically are of a far higher risk
In LWF's Fire Engineering blog series for Architects and others involved in building design, we have been looking at firefighting. In part 17, we began to look at how firefighting is undertaken by the Fire Service and their objectives and modes of operation when arriving at a fire. In part 19, tactical firefighting is discussed.While the general objectives of tactical firefighting were given in the last blog, there are various methods used by firefighters...
In LWFs blog series for healthcare professionals, the aim is to give information on best practice of fire safety in hospitals and other healthcare premises. In part 51 of this series, we were looking at the potential for fire spread from one area of a building to another through external surfaces, before moving on to begin to look at the necessary arrangements for car parks. In part 52, we continue on that theme by considering...
In LWFs blog series for those who work in Facilities Management or who have an interest in or responsibility for fire safety we have been looking at fire safety engineering. In part 8, we looked at how ASET (Available Safe Egress Time) is calculated and how this should always be more than the RSET (Required Safe Egress Time). While ASET involves a series of calculations relating to fire growth and the building itself, RSET, also...
In LWF’s fire engineering blog series for Architects and others in the business of building design, we have been looking at firefighting. In part 16, we discussed first-aid firefighting by the occupancy and the use of hose reels to do so. In part 17, we will begin to look at firefighting from the point of view of the Fire Services.The particular objectives of the Fire Service in a given situation will be decided upon...
In LWF’s blog series for healthcare professionals, the aim is to give information on best practice of fire safety in hospitals and other healthcare premises. In part 50 of this series, we discussed the potential for external fire spread including calculating unprotected areas and consideration of the surfaces of external walls and roofs. In part 51, we continue looking at external fire spread, starting with junctions of different elements.At the junction of wall and...
The Wohl Neuroscience Institute - Fire Safety, Strategy & Engineering
Key Facts: Client: King’s Clinical Neuroscience Institute Project Manager: MACE Ltd Designers: Devereux Architects/Allies and Morrison Approximate Size: 7,400m2 Description of the Project:...
Fire - The External Risk
When we consider fire safety, our focus is normally from within, what can we do to prevent the occurrence of fire and how we can limit its damage.Â Whilst this is the correct stance to take, we m...
Evacuation Modelling - Factor in Human Behaviour
Evacuation of buildings can be analyzed in different ways. Approved Document B (ADB) which provides guidance on meeting the requirements of the England and Wales Building Regulations with regard to fi...