Dead Leg in water system

Dead Leg in water system and its Limit as per different Regulatory Guidelines like EU Annex1, WHO TRS 970 and so on

Dead Leg in water system

What is mean by dead Leg in water system used in the pharmaceutical industry ?

Dead leg in water system is referred as Length of non-circulating pipe (where fluid may remain static) that is greater than 3 internal pipe diameters. Dead leg is the dictated by the Length-to-Diameter ratio.

If the Purified water system contains a dead leg, then water will not circulate continuously, which can encourage the development of biofilm So Purified water system piping should have zero dead leg structure.

Below are some regulatory Guidelines reference which describes about Dead Leg of water system concepts:

Note as per EU Annex 1 :

Water treatment plant and distribution systems should be designed, constructed, installed, commissioned, qualified, monitored and maintained in such a way that it should prevent microbiological contamination and to ensure a reliable source of water of an appropriate quality. Measures should be taken to minimize the risk of presence of particulates, microbial contamination/proliferation and endotoxin/pyrogen (e.g. sloping of piping to provide complete drainage and the avoidance of dead legs).

Note as per the WHO TRS 970 – Annexure II:

Dead legs in the pipework should be minimized through appropriate design work and as per guide it should not significantly exceed three times the branch diameter as measured from the ID pipe wall to Centre line of the point-of-use valve where significant stagnation potential exists.

Note As per US FDA guide 793 (High Purity water system) :

One common problem with piping is that of “dead-legs”. The proposed Regulations defined dead-legs as not having an unused portion greater in length than six diameters of the unused pipe measured from the axis of the pipe in use.

Note as per PMDA Guideline, Japan : 

As water will readily stagnate at “dead legs” occurring in T-shaped branches from the main piping leading to a closure mechanism such as valves, the distance between the diametrical axial center of the main piping and the closure mechanism in use should not be longer than six times to the inner diameter of the branch, but desirably not longer than three times if possible. Measuring instruments should be a sanitary type free of stagnation water .

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