Building Regulations and Structural Fire Resistance

England and Wales

Provision for structural fire resistance of buildings is embodied in Part B of Schedule 1 of the Building Regulations 1991 as follows :

“The building shall be designed and constructed so that, in the event of fire, its stability will be maintained for a reasonable period”.

How this requirement might practically be achieved is the subject of this publication.

Approved Document B 2000 interprets the requirements of the Building Regulations and states that the stability criterion will be satisfied if

“the load bearing elements of the structure of the building are capable of withstanding the effects of fire for an appropriate period without loss of stability”.

The Approved Document contains detailed provisions for the maintenance of structural stability in fire. These are intended to provide guidance for some of the most common building situations.

Guidance on “appropriate periods” for different building occupancies is given in Table A2 of the Approved Document (Summarised in Table 1). However these fire resistance periods are not mandatory. The Approved Document states that:

“There is no obligation to adopt any particular solution contained in an Approved Document if you prefer to meet the relevant requirement in some other way”.

The Approved Document goes on to suggest “other means” to demonstrate compliance by stating that:-

“Fire safety engineering can provide an alternative approach to fire safety. It may be the only viable way to a satisfactory standard of fire safety in some large and complex buildings and in buildings containing different uses. Fire safety engineering may also be suitable for solving a problem with an aspect of the building design which otherwise follows the provisions of the document”.

The most important aspects of the Approved Document concerning structural fire resistance are:

  • Fire resistance periods are based on building height only
  • The height of a building, for the purpose of determining fire resistance, is   measured from the ground to the floor of its uppermost storey. The top storey is not included. (Figure 3)

  • A reduction of 30 minutes in the required fire resistance may be applied to most types of nondomestic occupancies less than 30 metres in height when an approved sprinkler system is installed
  • The maximum fire resistance period for superstructure and basements is 120 minutes
  • Compartment sizes can be doubled in many instances where sprinklers are installed
  • All non-residential buildings over 30m in height must now be equipped with sprinklers
  • Structural elements of open deck car parks require only 15 minutes fire resistance. (The majority of universal steel sections have 15 minutes inherent fire resistance and thus most steel framed open deck car parks do not now require structural fire protection.)

Scotland

In Scotland compliance is required with the Technical Standards of the Building Regulations. Approval must be gained before construction takes place; one cannot build at risk.

Fire resistance requirements are contained in Regulation 12 to the Building Standard (Scotland) Regulations 1990 which state that

“every building shall be so constructed that, for a reasonable period, in the event of a fire... its stability is maintained.”

The measures which should be followed to ensure that this regulation is met are contained in Part D2 of the Technical Standards: Structural Fire Precautions. Many of the provisions outlined in Part D are designated as functional standards which contain references to deemed to satisfy standards. These may be descriptive or refer to documents such as British Standards. The introduction to the Technical Standards contains the following statement:

“Compliance with the Regulations: Regulation 9 sets out three ways by which the requirements of the Regulations can be satisfied:

  1. by compliance with the relevant standards set out in the supporting Technical Standards; or
  2. by conforming with provisions which are stated in the Technical Standards to be deemed to satisfy the relevant standards; or
  3. by any other means which can be shown to satisfy the relevant standards.”

The third of these statements is taken to mean that it is not necessary to follow the requirements of the technical standard if it can be proven that an alternative method meets the provision of the functional standard.

A relaxation of the requirements given in Technical Standard D is possible where alternative methods of fire protection can be shown to give equivalent levels of safety to those required in the standard. In such situations the local Building Control Officer, often assisted by the Scottish Development Office, may request compensatory features.

Typical of the type of structure which has been designed using an alternative method, in this case a fire engineering approach, is the stand at the Glasgow Celtic football ground in Parkhead.

The most important aspects of the Technical Document concerning structural fire resistance are :

  • The maximum period of fire resistance required is 240 minutes for certain types of high hazard storage buildings.
  • Fire resistance requirements are based on a combination of building height, floor area and cubic capacity of a building or compartment. situations.
  • Structural elements of open deck car parks require only 15 minutes fire resistance. (The majority of universal steel sections have 15 minutes inherent fire resistance and thus most steel framed open deck car parks do not now require structural fire protection.)

Northern Ireland

In Northern Ireland new Building Regulations came into force in November 1994. The fire safety requirements for these regulations are supported by Technical Booklet E which contains provisions regarding structural fire resistance, compartmentation etc. similar to those in the Approved Document for England and Wales. Unlike the provisions of the Approved Document which are for guidance, the provisions of Technical Booklet E are deemed to satisfy the requirements of the Building Regulations. Where the provisions of the Technical Booklet are not followed then the onus falls on the designer to show that the requirements of the regulations can be met by other means.

Source: Corus   

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