Legionella Prevention Queries

[churchill]

Hi guys,

I've been doing a bit of investigation into legionella prevention in commercial water systems and have a few questions. A few project specifications that I've come across have suggested pasteurising HWS calorifiers once a week, and heating them to 60°C for an hour.

1. Generally, is 60°C for an hour generally sufficient?
2. Is once a week a sufficient time period?
3. On systems with secondary HWS returns I would have thought that it'd be sensible to run the HWS circulation pump at the same time, in order to pasteurise water out in the pipework too?
4. I'm assuming pastuerisation is never carried out on HTG circuits?

I appreciate that some of the answers are very system dependent, but I'd be interested to hear thoughts on the above.

TIA!

 

[oz-plumber]

With stored hot water the temperature should be a minimum of 60 C all the time, preferably 65 C.

Secondary return systems should have a water temperature at the temperatures mentioned above.

If you have a secondary return system of a lower water temperature then you will need a UV filtration unit installed into the piping system which will kill off bacteria.

As for heating systems, the water is generally treated with chemicals and should have suitable backflow prevention devices that do not allow the heating water to enter the potable water supply.

Commercial hot water systems, as you state, have many variations and variables.
There are some basic principles which have to be adhered to, but how you achieve those in different systems can get quite involved.

I stand to be corrected, but I saw an article once that said that a lot of the Legionella finds were on the outlet side of the taps, in the tap breaches and water outlets and aerators.
Not sure how you would solve this problem unless you ran 65C water through the taps.
Could be quite hard to do, particularly when the TMV's have a shut off at 60C.

I'm sure you can find Government and Health Regulations that will answer your questions in greater depth and detail.

 

[Worcester]

In a commercial system, once a week isn't enough.

All you ever wanted to know:

see here: HSE - Legionella and Legionnaires' disease
and specifically HSE - Legionnaires' disease - Risk systems - Hot and cold water systems
and http://www.hse.gov.uk/pubns/priced/l8.pdf
and this: http://www.hse.gov.uk/pubns/priced/hsg274part2.pdf