By: William Jackson
Submitted: 2010-12-16 00:30:10 | Word Count: 452
Taking cooling tower and
[ advertisement ]
evaporative condensers aside, a large proportion of Legionella problems relating to domestic water systems stem from hot water cylinders. Granted, it tends to be showers that actually create the fine mist or spray that transmit the bacteria but the source of the bacteria seem largely to come from stored hot water. One of the principal reasons for this is the apparent conflict between two separate bits of guidance; the Legionella guidance (ACOP L8) and the Anti-Scalding regulations. ACOP L8 recommends that hot water is stored at 60C in the cylinder and distributed such that it reaches the supplied outlets at a minimum of 50C thus avoiding the temperature at which Legionella are able to grow effectively. The Anti Scalding regs state that where vulnerable people have access to the water services (e.g. nursery or healthcare setting) then 50C would be deemed at scald risk and water should not be supplied outside the range of 39 - 43C. On the face of it this would present a problem, the ideal solution is that the water is stored at 60C and reached the point of use at 50C but is blended down, by means of a thermostatic mixer valve (TMV) or blender tap, to a useable temperature. However, this is fine for new builds / refurbishments, but to retro fit TMVs can be a very costly and time consuming exercise with a number of organisations preferring to turn the hot water cylinder itself down to around 40C. This then provides water at a useable temperature for washing etc but the whole hot water system then falls within the ideal range for bacterial growth. One additional problem with TMVs is that of correct installation, having been given the advice that these valves need fitting, it is not uncommon for one central blending valve to be installed in the plant room or one valve used to serve the whole wing of a building. ACOP L8 states that TMVs should be installed ‘as close to the point of use as possible’ essentially to avoid long runs of pipe with water at non-compliant temperatures, but unfortunately does not give a definitive distance. TMVs are becoming more and more common, with talk of them becoming compulsory in the Building Regs, but there has been increasing evidence of Legionella colonization downstream of TMVs. This combined with vulnerable people is not ideal. For more information regarding TMVs or Legionella Management in general please call us on 01284 724 503 or visit our website www.nemco-utilities.co.uk
Author Resource:-
Charles has supervised the installation of domestic water systems for more than two decades. He works as a Public Health and Safety consultant and holds a diploma on Public City.
