Posted By Julian Meer (work) A coleague of mine is wanting to define the term "dead leg" re. a water system so our employees can go out and find them as part of a training session on legionella and for us to then design them out. To me, as a once plant chemist turned safety practitioner, who has helped unblock more process lines than I can remember (and successfully!), the term is intuitive and I have advised him to look for the classic situations of poor turbelence, e.g., blanked off lines, infrequently used outlets, elbows, tees, etc, etc., i.e., a factorial approach. However, given the absence of a definition of "dead leg" at large, including within L28, has anyone had a high degree of sucess in providing a practical "all encompassing" definition liked by the layman and practitioner alike? I don't really want to advise recourse to theoretical turbelence calculations at this first pass stage.

Posted By John Webster Roger, I can see what Julian is driving at. A short dead leg, such as a capped or valved off tee would not normally be considered a dead leg as there will be turbulence/vortex formation etc which should prevent the sort of conditions beneficial to Legionella. I suspect he is looking for some length:diameter ratio below which, under normal main line flow conditions, the branch could be considered part of the main line. As a former process engineer, I would consider any branch not as short as practicable to be a potential problem. That would mean that the only fitting after the branch tee, weldolet, threadolet etc is the terminal fitting - be it plug, cap, blank or valve, and that any intervening run of pipe is no longer than necessary to carry the fittings. If this cannot be achieved, or if the branch is downwards the termination should then be a valve (capped or plugged). Where the termination is a valve, this must be opened to flush periodically as part of the control programme. Sorry, Julian, I don't have any regs etc to quote, but I expect that backs up the sort of good practice you are familiar with. John