5 TOTAL HEAT OUTPUT OF FIRES

5.1 Figures for the heat release rate (RHR) of known fuel
combinations were compiled for various storage and
process risks in industrial buildings by the Fire
Research Station (see Appendix 2, Reference 1), but
Were categorised in a way unhelpful to smoke control
designers. These data were later revised to provide the
necessary basis for smoke control design (see Appendix 2,
Reference 2). The National Fire Prevention Association
(NFPA) of America have similarly compiled RHRs for
various fuels following experiments (see Appendix 2,
Reference 3). Further data for specific fuels have also
been compiled by the FRS (see Appendix 2, Reference 4).
Appendix 4, Tables A4.1-A4.3 list the various fuels and
fuel arrays, from both UK and USA references.
5.2 For storage risks there is a wide range of values of RHR
for essentially very similar storage categories, eg.
goods stacked in cardboard cartons.

It is a fundamental principle of smoke ventilation that the RHR
chosen for the design fire will affect the calculated
ventilation area or rate of exhaust. Storage risks may also
vary from the initially chosen fuel, eg. glassware in cardboard
cartons to plastic components in cardboard cartons. The nature
of the occupancy (risk) will not have changed (ie. storage),
but the potential RHR will, perhaps reducing the value of the
smoke control system. This can, to a certain extent, be
alleviated by designing the system to deal with the worst-case
scenario for the risk. Table 2 provides the data in Table A4.1
(storage risks) in terms of upper and lower limits for the
various storage categories. The values provided are RHR per
square metre (plan area) for each metre height of storage.
TABLE 2 RATES OF HEAT RELEASE FOR VARIOUS STORAGE CATEGORIES,
PER METRE HEIGHT OF FUEL

Storage Range of RHR
(kW/m²/m)Loose wood & wood products,
Inc. wood cribs & pallets;
Upright wood storage.
Stacked wood & wood products,
Inc. furniture; books;
Crated objects.
Cardboard & paper products,
Inc. stacked or loose
cardboard boxes or cartons
which are empty; cardboard
tubes or reels; mailbags,
Any storage in cardboard boxes
or cartons*.
Loose or stacked plastic
prodcuts, inc. PP & PE films
in rolls; PU & PS Insulation
Boards; PE Trays.1800 - 2900
30 - 720
120 - 240
160 - 1200
260 - 1280* NB Excludes the apparently anomalously high values for
PS jars in cartons.

The total heat output is calculated from the product of the
plan area of the fire, its height and the appropriate RHR
values.

5.3 Where information on the exact nature of the fuel
Is unknown, eg. speculative buildings, and the local
regulatory authorities have not recommended the design
fire size and RHR, then a range of RHR of 60-500kW/m²/m
is recommended, with a minimum ·assumed storage height of
2m (see Appendix 2, Reference 5). Further design details
for speculative buildings may be found in Section 14.
5.4 The designer should use both values of RHR from Table 2
for the particular occupancy examined, or as in 5.3 above
for speculative buildings, and calculations performed to
determine all of the necessary design parameters. From
these two sets of results, the worst case parameters
resulting from either value of total heat output should
then be used in the design.
5.5 For specific non-storage occupancy or liquid fuel risks,
then the RHRs in Tables A4.2 and A4.3 should be used to
determine the total heat output.