8
G3 GUIDANCE SECTION 3.9
The discharge pipe (D2) from the tundish should terminate in a safe place
where there is no risk to persons in the vicinity of the discharge, preferably
be of metal and:
1 Be at least one pipe size larger than the nominal outlet size of the safety
device unless its total equivalent hydraulic resistance exceeds that
of a straight pipe 9m long i.e. discharge pipes between 9m and 18m
equivalent resistance length should be at least two sizes larger than the
nominal outlet size of the safety device, between 18 and 27m at least 3
sizes larger, and so on. Bends must be taken into account in calculating
the ow resistance. Refer to Table 01 on page 9 and the worked
example.
2 An alternative approach for sizing discharge pipes would be to follow BS
6700:1987 Specication for design installation, testing and maintenance
of services supplying water for domestic use within buildings and their
curtilages, Appendix E, section E2 and table 21.
3 Have a vertical section of pipe at least 300mm long, below the tundish
before any elbows or bends in the pipework.
4 Be installed with a continuous fall.
5 Have discharges visible at both the tundish and the nal point of
discharge but where this is not possible or is practically difcult
there should be clear visibility at one or other of these locations.
Examples of acceptable discharge arrangements are:
i Ideally below a xed grating and above the water seal in a trapped gully.
ii Downward discharges at low level; i.e. up to 100mm above external
surfaces such as car parks, hard standings, grassed areas etc. are
acceptable providing that where children may play or otherwise come
into contact with discharges a wire cage or similar guard is positioned to
prevent contact, whilst maintaining visibility.
iii Discharges at high level; e.g. into a metal hopper and metal down pipe
with the end of the discharge pipe clearly visible (tundish visible or not)
or onto a roof capable of withstanding high temperature discharges of
water and 3m from any plastics guttering system that would collect such
discharges (tundish visible).
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