BS 476-20 Fire tests on building materials and structures — Part 20: Method for determination of the fire resistance of elements of construction (general principles)

1 Scope
This Part of BS 476 describes a procedure for a laboratory test for the determination of fire resistance of elements of construction.
NOTE The titles of the publications referred to in this standard are listed on the inside back cover.

2 Definitions
For the purposes of this Part of BS 476, the definitions given in BS 4422 apply, together with the following.

2.1
associated construction
a form of construction that may be required for the testing of some elements of construction and to which the test specimen is connected, e.g. the wall
into which a glazed element would be fitted

2.2
collapse
the mechanical failure of the complete specimen that allows it to fall from the position into which it has been fixed

2.3
fire resistance
the time for which an element of building construction is able to withstand exposure to a standard temperature/time and pressure regime
without a loss of its fire separating function or loadbearing function or both

2.4
fixity
the conditions at the edges, ends or supports of a test specimen through which the applied test load is either being applied or reacted (either directly or by
induced moments)

2.5
restraint
the conditions at the edges, ends or supports of a test specimen through which the movement of the specimen is constrained (Examples of restraint are
shown in Figure 1.)

2.6
furnace closure
a suitable form of construction designed to fill the space between the permanent opening of the furnace and the test construction so that the
specified furnace conditions are maintained for the duration of the test without interconnection between the test construction and the furnace
closure and which has no significant effect on the behaviour of the test specimen

2.7
impermeability
the ability of a specimen of a separating element to restrict the egress of hot gases from the unexposed face of the specimen causing ignition of the cotton
pad

2.8
insulation
the ability of a specimen of a separating element to restrict the temperature rise of the unexposed face to below specified levels

2.9
integrity
the ability of a specimen of a separating element to contain a fire to specified criteria for collapse, freedom from holes, cracks and fissures and
sustained flaming on the unexposed face

2.10
loadbearing capacity
the ability of a specimen of a loadbearing element to support its test load, where appropriate, without exceeding specified criteria with respect to either
the extent of, or rate of, deformation or both

2.11
specimen
an element of building construction provided for the purpose of determining either its fire resistance or its contribution to the fire resistance of another
building element

2.12
sustained flaming
flaming that is visible with the naked eye and that remains visible for an uninterrupted period of not less than 10 s

2.13
test construction
a complete assembly of a specimen and its associated construction if incorporated

2.14
separating element
an element that is required to satisfy the criteria of integrity and insulation, in addition to loadbearing capacity if applicable, for the purposes of
maintaining separation between two adjacent areas of a building in the event of a fire