Rank: Guest 
|
Posted By Stuart Nagle
I would be grateful for some assistance on a particular area on the subject
of 'dead legs' in hot and cold water systems.
A problem has arisen where a health care building (day centre with capability
of undertaking day surgery) is at present under utilised.
Examination of the hot and cold water system has revealed a lot of dead legs
in the systems which idealy should be removed, but client says no money for this and
sampling contunually shows regular peaks in bacterial contamination of the
systems.
Whilst regular dosing and flushing was instigated by the client (own staff) the readings imply that this
is not being managed (noe recorded correctly).
By way of investigation, a contractor has stated that he read that dead legs
should not be longer than 2.5 times the diameter of the pipe (e.g. 15mm pipe
X 2.5 = 37.5mm)
There are numerous documents and standards that 'indicate' very differing
acceptable lengths of dead legs and relate to various methods of control, including
trace heating etc.
I wondered if any of you could point me to 'definitive standards' that would either
exemplify the contractors belief's (as above) or specifically show the maximum
lengths related to pipe size and water capacity for different systems.
So far I have looked at various BS standards, CIBSE, NHS and BSRIA documents
(as well as L8) without being able to obtain such a definitive answer....
Stuart
|
|
|
|
|
|
Rank: Guest
|
Posted By John Webster
Stuart
A true description of a deadleg should define a length:diameter ratio at the typical flow velocity for the main line. I am not aware of any such definition in the UK, although the US Food & Drug Administration (FDA) does define a deadleg as 6xpipe diameters measured from the centre line of the flow. This is the required US standard for potable and pharmaceutical water and is quoted in their equivalent of Building Regs. However, installers of high purity process water (eg for electronics) would consider this excessive, with 2.5:1 being the norm and 2:1 the achievable.
I expected that the NHS Estates technical notes would offer some help (SHTMs 2027 and 2040) but no. They do, however, state that a spur must not exceed 5 metres, but this can only apply where the end of the spur is a regularly used outlet. I also picked up a good tip to ensure auto-flushing urinals are fitted at the furthest point of the longest runs!
My conclusion - any deadleg over ~6 diameters will need to be flushed regularly, but when eliminating deadlegs try to get them as short as possible below 6 diameters.
Cutting the pipe, installing a simple service valve, and leaving the deadleg disconnected should in most cases be a straightforward job, and leaves the system open to reconnection if needed at a later date.
John
|
|
|
|
|
|
Rank: Guest
|
Posted By Stuart Nagle
John
Thanks for your response, I had already assumed that the shortest possible length
was the way forward here, but was trying to see if anyone had an inkling as to where the
the 2.5 X diameter was located (in writing) but seems no such luck.
I have noted in various specification and standards completely different 'maximum' lengths
for deadlegs, all at odds with one another and completely contrary to the best advice
given, even in L8!!!!
Once again many thanks for your input... most welcome...
Stuart
|
|
|
|
|
|
Rank: Guest
|
Posted By Glyn Atkinson
"No money available for safety related repairs to a potentially hazardous water system that could come into contact with the public !! - Administrative scandal !! " - bit long winded, but a good headline for the local paper to have on file for future reference, or as an investigative story ??
Or there's always that wonderful "anonymous" phone call to the local HSE office??
|
|
|
|
|
|
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.