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Special report: fire safety

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technical & practice

The new Approved Document B, published on 20 January, comes into effect on 1 July and replaces the current regulations which have been in place since 1992. In the light ofconcerns about health and safety, it introduces requirements for fire- strategy risk assessments, clarifies outdated guidance and, for the first time, provides guidance on insulating core panels.

Other amendments include texts on fire-fighting shafts, domestic egress, windows and means of escape for cafe-type premises on upper floors. The merits of certification and accreditation are highlighted, but are not mandatory under this revision.

The new document gives information specifically relating to educational buildings: the life-safety aspects of Building Bulletin 7 are now covered by the Department of Environment, Transport and Regions. It also includes a provision for compartmentalisation and/or sprinkler protection in single- storey retail buildings with a floor area exceeding 2000m2.

The most significant addition is the introduction of a new Appendix F: Fire Behaviour of Insulating Core Panels Used for Internal Structures. This is the first time that the document has offered guidance on sandwich panel construction, recognising its increasing use in contemporary buildings.

Headings include the fire behaviour of the core materials and fixing systems, fire-fighting, design recommendations and specifying panel core materials, fixing and jointing systems.

The guidance makes direct reference to internal structures, with only brief comments for external insulating building envelopes. There appears, therefore, to be a misconception that the problems associated with combustible- core sandwich panels, and hence the need for guidance, is limited to internal panels only and does not affect the external use of panels. This is patently not the caseas several high-profile fires have involved the external panel building envelope itself becoming part of the fire load. Given that such constructions can be said to be life-threatening, to the emergency services for example, they should be considered in the next tranche of guidance. The role of risk assessments in the new regulations means that the hazard to those who will have to deal with a fire, should be given a high proiority - and early consideration - in the design process.

The delamination of all core types in fire is mooted, recognising that problems with mineral wool cores are perceived to be less than those with polymeric cores. The Regs suggest that fire spread can occur behind all panels with ensuing problems for firefighters and there is a positive recognition of the hazards from black toxic smoke and from flashover - common to polystyrene and polyurethane insulation cores.

Correct detailing of the insulating envelope should ensure that the combustible insulant is fully encapsulated by non-combustible facings which remain in place during a fire. It is important that cavity barriers be incorporated into cavities created by panel arrangements.

The 1999 iacsc Guide is recommended as suitable guidance for most insulating core panel applications (that is, by implication, most contemporary buildings). Conscientious designers will find this to be totally inappropriate as the iacsc Guide was not intended to address applications outside the very specialist food storage and distribution industry and contains insufficient quantitative information on the fire performance of core materials. Mineral fibre cores are suggested for cooking areas, hot areas, bakeries, fire breaks in combustible panels, fire stop panels and for general fire protection. Non-combustible panels are 'suggested' for high-risk areas, at intervals in walls and ceilings.

It would seem that, with the introduction of the Construction Products Directive, harmonisation of European fire performance testing and classification is imminent. The detr is responsible for creating a Supplement to Approved Document B which is expected at the end of this year or early 2001. This should clarify the situation vis-a-vis the uk's existing Class O performance classification and the seven new Euroclasses for categorising construction products.

Also in the pipeline is a bsi document under the working title bs 9999. This seeks to address the plethora of fire legislation currently enforceable in the uk so that rational decisions can be made based on the latest research, standardised tests and experience of real fire incidents.

In conclusion, the new Approved Document B makes minimal changes for traditional design and construction elements. However there aresignificant implications for contemporary fast track panel construction and there are definite guidelines for the thorough risk appraisal of structures. It is hoped that these will be highlighted further when the government publishes its supplement detailing the harmonised eu classification requirements for both fire resistance and the reaction to fire performance of construction products.

Taken as a whole, this document is a good start which should improve the safety of users and firefighters alike.

Anna Cherry is a writer and principal at Cherry Communications, Blaengwynlais, Caerphilly

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