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
In July 2005 the Office of the Deputy Prime Minister (ODPM) issued a revision of the Approved Document B (ADB) for consultation. The amendment was considered necessary to adapt to the current standards and changes in construction practise, approaches to European terminology concerning fire rating and an integration of other technical references and associated legislation. As such the proposed new edition of ADB has been split into two parts – Volume 1 (Dwellings) and Volume 2 (Buildings other than Dwellings).
Our December Bulletin "ADB - Proposed Revisions" commented on the contents of Volume 1 of the consultation document focusing on the fire safety precautions in dwellings. Therein the following main amendments compared with current ADB 2000 according to fire safety were discussed.
In this bulletin we focus on the second part of the proposed new ADB Volume 2 concerning “Buildings other than dwellings”.
Fire safety requirements for specific purpose groups are given in specific standards or codes which address the issue of specific hazards in buildings (e.g. Firecode HTM 81 for fire precautions in new hospitals); however, the ADB still embodies the basic document for fire safety aspects within the design.
Besides textural changes (format and layout) the modifications of ADB Volume 2 deal with an increased integration of fire safety precautions regulated in related codes and standards. Even if ADB Volume 2 does not discuss the integrated fire safety measures in detail it increasingly refers to sufficient standards, codes and documents that give guidance in the design; e.g. ADB Volume 2 refers to the Fire Protection Association Design Guide that insurers use as a basis to assess the risk.
The standardisation of ADB reduces the regional variations in the use of building regulations and sets up a regulation on a National level. The amendments that are made in this context do not propose new requirements; the document is more a collation of existing requirements composed into one document for designer’s attention. The main topics forming a new part or a part of increased consideration in ADB Volume 2 are:
Besides the integration of other codes and standards the ADB – Volume 2 shows the following innovations mostly resulting from experience and practise.
These topics regarding standardisation and innovation are discussed in the following paragraphs.
It is not possible to detail all changes that are within the revised ADB, as such in this bulletin only the major amendments have been considered.
Referring to the intention of ADB Volume 2 to ensure a reasonable standard of fire safety for all occupants in a building, the means of escape for people with disabilities, regulated by BS 5588-8, Part M of Building Regulations and the Disabled Discrimination Act (DDA), are to be integrated in ADB Volume 2. Following the guiding principle “People regardless of disability, age or gender, should be able to gain access to buildings”, ADB Volume 2 recommends measures for the evacuation of people with disabilities. Examples of measures are: provisions of refuge areas (places of temporary safety) in every storey with disabled access, communication systems to call for help or warning systems for people with impaired hearings.
Referring to BS 5588 – 11 the ADB Volume 2 gives guidance for the means of escape for small premises. Small premises are defined premises with a single occupancy with not more than a basement, a ground floor and an upper floor and with a storey area of not more than 280 m2.
The requirements for small premises in terms of means of escape are different from the general requirements in ADB Volume 2. Due to the limited size of the storeys, short travel distances and limited numbers of occupants the risk for evacuation in case of a fire is decreased. These boundary conditions facilitates e.g. a increase of the permitted single travel distances in the ground floor of small premises up to 27 m. The current ADB allows a maximum single travel distance of 18 m in offices and 25 m in industrial buildings and storages regardless of the size of the premise. Hence ADB Volume 2 enables a greater room for creativity in the design of small buildings.
Based on the guidance issued by the Scottish Building Standards Agency, ABD Volume 2 now gives instruction for the fire design of care homes. Prospectively, in every new care home an automatic fire detection and alarming system (category L1) and a residential sprinkler system are to be provided. These measures improve the conditions for evacuating people and consider the limited abilities of persons living in care homes.
To further support the means of escape in care homes the ADB is also to be revised concerning the requirements for compartmentation. The area of a compartment is to be limited to 1500 m2 and additionally has to be subdivided into at least two sub-compartments of maximum 750 m2. Current ADB recommends designing health care and other institutional premises in accordance to “Firecode” documents.
Additionally rooms deemed to be of a higher hazard are to be enclosed with a fire resistant construction to minimize the risk for adjoining areas in case of a fire within one of these rooms and to maximize the time available for evacuation. To reduce the needed time for evacuating people in rooms affected directly by fire, the number of persons in sleeping rooms is limited to four persons.
Means of escape
Regarding the means of escape ADB Volume 2 does not indicate any fundamental amendments.
However, aspects referring to travel distances and capacity of escape routes are to be reconsidered due to recent research. Thus, the maximum travel distances in industrial, storage and other non-residential premises, containing a higher hazard, are to be reduced to 12 m (single direction), and 25 m (more than one direction). Currently, travel distances of 25 m (single direction) and 45 m (more than one direction) are permitted in industrial, storage and other non-residential premises regardless the level of hazard.
The dimension of the necessary width of escape ways is to be modified. According to ADB Volume 2 a door with a width of 750 mm is sufficient for evacuating up to 60 persons. Current regulation (ADB 2000) requires 750mm door width for 50 persons.
Further amendments are to be a maximum of provided regarding to phased evacuation in buildings. In phased evacuation at first people in the storey directly affected by the fire and the people with reduced mobility are to be evacuated. Current ADB 2000 further recommends evacuating the storey above the fire floor immediately. But practise and recent research has shown that people evacuation from above restrict the movement of people escaping from the fire floor. Therefore ADB Volume 2 provides only the evacuation of people on the fire floor itself and people with restricted mobility at first. If necessary afterwards the other storeys can be evacuated, two floors at a time.
In buildings designed for phased evacuation current ADB 2000 enables the designer not to discount stairs. Because of the high level of protection afforded to the stairs, it does not have to be assumed that a stair is out of use in the case of a fire. Therefore reduced stair widths are possible because all stairs can be provided to ensure the necessary capacity.
ADB Volume 2, however, requires discounting stairs in high rise buildings (floor height greater than 30 m) even if they are protected with a smoke control system or a lobby. This amendment is being taken to prevent mutual obstruction of fire fighting persons entering and people leaving the building designed for phased evacuation in case of fire. Thereby the enlarged stair width increases the capacity of the stairs and decreases the density of persons in a stair case at the same time. So the fire fighting access to the building and the movement within the building is to be improved.
Fire Fighting access and water supply
The main amendments in requirements concerning fire fighting are dealing with water supply. To reduce the time for fire fighters to initiate their operation and to enable a prompt action ADB Volume 2 recommends private hydrants to be provided when a building with a compartment greater than 280 m² is built more than 100 m from a public hydrant. Depending on the existence of fire mains within the building the private hydrants have to be provided within 100 m from a dry rising inlet or within 75 m of any point of the perimeter of the building. Alternatively a charged static water tank or other water sources can be use for the water supply, on the condition that at least 45,000 litre of water are stored or provided at all times of the year and that the water sources are accessible with pumping appliance.
In terms of Environmental protection concerning fire suppression ADB Volume 2 refers to the Pollution Prevention Guidelines (PPG 18) that require the provision of containment areas for contaminated water in large commercial and industrial sites and small commercial and industrial sites that are deemed to be high risk.
A contamination of water takes place when hazardous substances that are stored or used in industrial processes are released in case of a fire and use the extinguishing water as carrier to reach ground water. To prevent the pollution of the ground water the contaminated water should be collected in containment areas.
However, it should be considered, that not the size of a site is decisive; much more relevant is the type and the quantity of the stored goods within the building, that may contaminate the run-off water.
For fire fighting within the building the criteria for the number of fire fighting shafts and hence the number of fire mains in fire fighting shafts is to be modified too. As the current ADB provides fire fighting shafts dependent on floor area and hose distances the criteria in ADB Volume 2 concentrates only on the hose distance. The reduction to only this single criterion for the provision of fire mains in fire fighting shafts enables more freedom in the design of a building without increasing the risk for fire fighting measure.
The proposed amendments in ADB Volume 2 improve the application of ADB to the use for design measures. Sections have been reviewed addressing to more clarity (e.g. “Concealed Spaces”). Regarding contents the amendments within these sections and also within the whole document are minor.
Mainly the proposed revision of the ADB 2000 can be summarized as a consolidation act. It simplifies the consideration of fire safety precautions within the design phase of a building because it increasingly refers to and integrates requirements from different sources.
ADB recommends measures to ensure an adequate fire safety solution for buildings; however, the measures in ADB are not mandatory. The relevant requirements for fire safety can also be achieved in an alternative way. Fire engineering solutions may be used as an alternative way to provide a high level of fire safety. This way fire safety can be insured for building designs that do not adopt to the fire safety approach recommended by the ADB.
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