GB, the pressure and flow needed at the top most outlet must be sufficient to operate a firefighting jet. (normally around about 7 bar but of course lower pressures will produce a jet). So, the first question is 'what minimum pressure does the attending fire & rescue service need at the topmost outlet?' Having got this little detail fixed the next question is can the F&RS achieve this by pumping into a dry riser? If, the F&RS cannot pump to achieve the pressure you have no alterantive but to consider a wet riser with appropriate booster pumps.
If we accept that pressure loss due to head is 0.1bar/metre head, the difference between 10 bar inlet pressure and 7 bar (nominal target) outlet pressure would suggest pressure loss of 3 bar or 30 metres. However Technical standards allow a dry riser up to 60 metres which would suggest that a 3.5 bar outlet pressure satisfies the Technical Standards. Would the F&RS accept this pressure? You are now schmoozing up to Regulation 23(1) of the Fire Safety (Scotland) Regulations 2006 if the F&RS are unhappy.
Lastly, I have fought fires off a dry riser 12 floors above ground level, but the hydrant pressures and flow rates were superb.
