Dead Legs: Lessons in Legionella Management

Now that Legionella testing has become more widely accepted, it is unsurprising that test results are sometimes returned as positive.  When the building has a proper Water Management plan (WMP), that positive result leads to immediate and predetermined action steps to remediate and normalize.  This is exactly what a quality system should do.  Allow for discovery, find and fix the problem, then confirm and validate resolution.  Many buildings however, still have not gone through the process of plan development and are perplexed by the positive result.  In some instances, owners may even feel that testing alone is an adequate precaution that allows them to check the box.  Unfortunately, this is the wrong mindset.  More appropriately we should consider a positive result to be an indicator of hidden problems, whereby an important fact-finding mission should be undertaken.  Translation? A “risk assessment” is needed. One of the primary areas of concern emanating from a technically-sound risk assessment are is locating the water system system’s dead legs.  These are the zones of the system that have been valved off, cut off, or not allowed to flow water (especially treated water) through the system continuously.  Examples include: auxiliary/secondary recirculation pumps and associated piping, the ends of cooling tower spray manifolds, and any isolated upper zone circulation patterns.  Lack of flow allows for accumulation of contaminants, loss of chemical protection, growth of bacteria and proliferation of bio-film.  Finding and eliminating the dead legs still may not guarantee a Legionella-free system, but is certainly a major step-forward and together with testing, will set the building on the right path to protection.


By John Caloritis

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