15 SIZING / SITING OF EQUIPMENT

All smoke control products should comply with the
requirements of the "SVA Guide to good practice on
application of smoke control equipment and systems" (see
Appendix 2, Reference 15). Extract equipment should
not exhaust at a rate likely to puncture the smoke layer
and should be sited in such a way as to not disturb the
smoke layer base. Particular consideration should be given
to High Racked Storage Areas since the smoke layer depth
is freguently very shallow in these buildings. (In this
context) mass flow rate and velocity should be considered
(see Appendix 2 References 16 and 17).
Rules used in the Industry are:
15.1 The size of natural and powered extract units should
be limited to prevent puncture of the smoke layer.
Reference 16, Appendix 2 shows methods of calculation
and limiting factors.
15.2 Natural extract ventilators should not be spaced
morethan 20m apart.
15.3 For natural systems, the preferred aerodynamic area
Of inlet should be at least equal to the aerodynamic
areaof extract. The designer should state the actual
ratio taken into account in calculations.
15.4 For mechanical systems, inlet resistance should be
considered when sizing equipment extraction and the
value should be stated by the designer.
15.5 Fan motors should be rated at temperatures compatible
with the system design, but should be sized to
operate at ambient conditions (288K).
15.6 Compressed air receivers should be capable of three
operations of the system after power failure.
15.7 Exhaust equipment should meet the specifications of
the relevant British Standard (see Appendix l,
References 3 and 4)