Posted By GavinR Hi Guys, I have a query regarding legionella growth in a closed system. We have part washers that run mains water (cold) to the 3 x machines. These m/c store the water and heat it to set temperatures for cleaning of parts. The 3 x different temperatures are 54 Deg C, 42 Deg C and 23 Deg C. They run consistently throughout the day (16 hours) and stop on nights. The mains supply is subject to Legionella testing and control measures and the tank. These washers are cleaned out every 4-5 weeks but i have concerns that they may be a potential source of exposure. When opened the washer vents a steam could into the surrounding area for approx 30 seconds to a minute. My question is within a closed system like this is 4-5 weeks a suitable incubation period for legionella to grow? I believe from the guidance (L8) that criteria for favouring growth is present but will the period of time the water is within the units sufficent? Cheers Guys.

Posted By Stephen Mitchell Hi Gavin Whilst I would not profess to be an expert on legionella, I have been on the IOSH Legionella Management course (which I readily recommend) and have some knowledge of controlling the risks. With regards to your question “within a closed system like this is 4-5 weeks a suitable incubation period for legionella to grow?” I assume that the water within the parts washing system is held for the 4-5 week period before the tanks are emptied and cleaned? If this is indeed the case then I would have to say that IMO based on my understanding that under the right conditions legionella can double at a frequency of 12 hours, then yes your 4-5 weeks is ample time for proliferation of legionella bacteria. Also based on the information you have provided I would say that (a) As the system is fed via mains water then legionella bacterium could enter the system. (b) As you have stated that your system has water at 54, 42 and 23 Dec C and the tanks also cool overnight, then with the exception of the 54 Deg C tank then temperature control is not occurring (50 Deg C for two hours will kill 90% of bacteria). You have not stated if parts pass through each tank in turn or not, if they do then cross seeding between tanks could occur. (c) Finally as you are undoubtedly aware legionella bacterium needs something to feed on; so you would need to check for nutrients in the water system; these nutrients may be in the form of sludge, sediment, scale, rust deposits etc or biofilm (slime) growth within tanks, pipe work etc. As for the level of risk then without seeing your system its not possible to say. Hope that helps Cheers Steve

Posted By Brian Hagyard GavinR As others have said it does sound as if Legionella could grow in your system. But does it pose a risk? You state that "steam" is expelled. If I remember my basic chemistry correctly, steam is above 100C so there should be no risk from this. Is there any other source of aerosol dispersion form these units? Brian

Posted By GavinR Hi, thanks for the responses so far. The machine in question runs at 53 Degree C but when the lid is opened the unit releases a mist. It looks to be a closed system without any release sources during operation. There is also a filter mist unit installed on all 3 washers to remove any oil mist emitted.

Posted By Brian Hagyard spell check is wonderful! Mew is obviously NEW.