NCC 2016 Volume One
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Section C Fire Resistance (Verification Methods)

Section C Fire Resistance (Verification Methods)

VERIFICATION METHODS

CV1

Compliance with CP2(a)(iii) to avoid the spread of fire between buildings on adjoining allotments is verified when it is calculated that—

(a)

a building will not cause heat flux in excess of those set out in column 2 of Table CV1 at locations within the boundaries of an adjoining property set out in column 1 of Table CV1 where another building may be constructed; and

(b)

when located at the distances from the allotment boundary set out in column 1 of Table CV1, a building is capable of withstanding the heat flux set out in column 2 of Table CV1 without ignition.

Table CV1
Column 1 Column 2
Location Heat Flux (kW/m2)
On boundary 80
1 m from boundary 40
3 m from boundary 20
6 m from boundary 10
Buildings on adjoining allotments

is a means to verify whether or not a building proposal achieves the requirements of in minimising the risk of fire spreading between buildings on adjoining allotments. A fire in one building should not cause the spread of fire to another building, because such fire spread potentially endangers public safety, health and amenity.

It is not compulsory for a designer to use . The designer has the choice of using:

  • to verify that a proposal achieves ;
  • the Deemed-to-Satisfy Provisions of Part C3; or
  • another means of verifying that will be achieved.

If is used to calculate the level of heat flux, it is important to calculate the level at all the points referred to in . The maximum level is not necessarily at the boundary. The size and shape of the openings will influence the level of heat flux.

Whether a material will ignite from radiant heat depends on the amount of heat and whether an ignition source (such as a spark) is present.

Examples

Examples

The following values give some typical examples of the amount of radiant heat necessary to ignite common materials used in buildings and their construction. Note, these figures should not be taken to be absolute, and may be subject to a range of variables.

  • Timber
    • Ignition in the absence of a spark 35 kW/m2
    • Ignition in the presence of a spark 20 kW/m2
  • Curtain materials
    • Ignition in the absence of a spark 20 kW/m2
    • Ignition in the presence of a spark 10 kW/m2

There are three mechanisms for transferring heat:

Conduction

Conduction is the transfer of heat from one source to the other when they are in contact.

Convection

Takes place when the flames or fire plume carry the heat to another body. Convection includes the carrying of embers from a burning body that can cause ignition of a second body.

Radiation

Radiation is the transfer of heat from one body to another. In essence this involves one body putting out enough heat to heat up another body without any form of contact, either directly or by way of flames or embers.

Radiation is the main mechanism for heat and fire spread between buildings.

By way of techniques developed in the field of physics, it is possible to calculate the amount of heat given off by a burning building. The answer depends on a number of factors, including:

  • the distance from the building;
  • the size and shape of the openings in the building;
  • the temperature of the fire, which will depend on the:
    • size of the fire, and
    • type of materials burning; and
  • the emissivity of any glass in openings in the building. The emissivity is, in comparatively simple terms, a measure of radiant heat reduction through a window opening. The maximum value is 1, but lower figures may be appropriate, depending on such factors as:
    • whether the opening is drencher protected, or
    • whether the opening is a fire window.

CV2

Compliance with CP2(a)(iii) to avoid the spread of fire between buildings on the same allotment is verified when it is calculated that a building—

(a)

is capable of withstanding the heat flux set out in column 2 of Table CV2 without ignition; and

(b)

will not cause heat flux in excess of those set out in column 2 of Table CV2,

when the distance between the buildings is as set out in column 1 of Table CV2.

Table CV2

Column 1 Column 2
Distance between buildings Heat Flux (kW/m2)
0 m 80
2 m 40
6 m 20
12 m 10