Legionella and TMV's

[robgraham]

I posted a query some time back about the advisability of having a heatbank set up with a TMV to control the DHW to something like 50C as suggested in the DIYWiki. My concern was that distributing water at this temperature could be a spawning ground for legionella but was querying if anyone knew anything about this - there was no answer !!

Well I've now got the answer and it confirms my suspicion that such an arrangement would be inadvisable :-

# 70 to 80 =B0C (158 to 176 =B0F) - Disinfection range # At 66 =B0C (151 =B0F) - Legionellae die within 2 minutes # At 60 =B0C (140 =B0F) - Legionellae die within 32 minutes # At 55 =B0C (131 =B0F) - Legionellae die within 5 to 6 hours # 50 to 55 =B0C (122 to 131 =B0F) - They can survive but do not multiply # 20 to 50 =B0C (68 to 122 =B0F)- Legionellae growth range # 35 to 46 =B0C (95 to 115 =B0F) - Ideal growth range # Below 20 =B0C (68 =B0F) - Legionellae can survive but are dormant

It is interesting that building regs in Scotland now require a TMV for baths in new builds but categorically state that the TMV must be as close to the outlet as possible and that the tank water temperature must be in excess of 60C.

Rob

[PeterK]

Well I've now got the answer and it confirms my suspicion that such an arrangement would be inadvisable :-

# 70 to 80 °C (158 to 176 °F) - Disinfection range # At 66 °C (151 °F) - Legionellae die within 2 minutes # At 60 °C (140 °F) - Legionellae die within 32 minutes # At 55 °C (131 °F) - Legionellae die within 5 to 6 hours # 50 to 55 °C (122 to 131 °F) - They can survive but do not multiply # 20 to 50 °C (68 to 122 °F)- Legionellae growth range # 35 to 46 °C (95 to 115 °F) - Ideal growth range # Below 20 °C (68 °F) - Legionellae can survive but are dormant

It is interesting that building regs in Scotland now require a TMV for baths in new builds but categorically state that the TMV must be as close to the outlet as possible and that the tank water temperature must be in excess of 60C.

Rob

I thought both thermal stores & heat banks use heat exchangers and the only thing that comes out of a hot tap is "mains" water. Some of this water could have sat in an internal heat exchanger for some time but that's no different to the hot water reservoirs on combi boilers.

PeterK

[Pete C]

Anyone aware of any legionalla illness/fatality occuring from plumbing in _domestic_ circumstances?

cheers, Pete.

[Andrew Gabriel]

There are none.

Legionalla seems to have become noticed about the same time people started trying to keep their water supplies sterile. This might be due to the resulting loss of natural immunity to the bacteria, which has likely been around for ages (it's naturally present in rain in small quantities). When a person who has lost their immunity through lack of exposure at home is then exposed to a non-sterile supply (often in hospital or other institution), they are much more vulnerable to pick it up.

If this is one of the main causes of infection (I'm not aware of any research on this, but the hypothesis fits the observations), it explains why you can't catch it at home -- you either have a contaminated supply and are hence immune, or you have a sterile supply.

[David Hansen]

On Wed, 31 Oct 2007 15:06:55 -0700 someone who may be robgraham wrote this:-

Didn't notice the question.

In large buildings it has been recommended for decades that domestic hot water is distributed round the building at high temperature and mixed down to a lower temperature at the fitting.

However, most houses are not large buildings and the extra complications of such an approach are unlikely to improve safety much. For example large buildings tend to have hot water being circulated constantly in the hot water mains, which gives time for the little nasties to breed nicely. Few houses have such a setup.

[Onetap]

I think I had answered it at the time, or a very similar query. Store at 60 degC, mix at the outlet, as recommended in the HSE's L8 document, which has been the commercial code of practice and guidance in the UK for some years. I think the range of temperatures above are from L8 but I can't be bothered to check.

It's nice you've managed to verify what (I think) I'd said, shame it took so long.

[Onetap]

I don't think the figures are collected by the HSE because the relevant legislation is the Health & Safety at Work Acts, which don't apply to domestic circumstances. Commercial building owners and managers have a 'duty of care' defined in law; householders don't.

I think it probably happens a lot (judging by the unbelievably hideous state of many domestic systems that I've seen), but no-one goes to the effort of sampling domestic water systems to verify the source of one infection. There may be numbers on the HSE website; I suspect they get lumped in with the bulk of 'source unknown' infections.

The only domestic case I know of concerned an American plumber who had a second home or cabin. He fired up the heating and had a shower shortly after arriving there for the first visit in several months. Afetr he became ill, he was being treated for a chest infection but wasn't tested for legionella until the penny eventually dropped and he realized he'd done a silly thing.

[Onetap]

This one; not quite as I had remembered.

http://64.233.183.104/search?q=cache:Hxt0SQsRsXIJ:

[David Hansen]

On Wed, 31 Oct 2007 15:06:55 -0700 someone who may be robgraham wrote this:-

To be complete this information would need to include how quickly they multiply. Minutes, hours or days.

Time information is given for the higher temperatures.

[Timothy Murphy]

I find the information I've read on Legionella rather unconvincing.

Why is it not raging in the cold water system in countries where the ambient temperature is in the "Ideal growth range"?

Is it in fact commonly found in domestic hot water systems? That must be easy enough to determine. If so, I would have thought it would be easy enough to kill the bacteria.

[robert]

ISTR that transmission to humans only occurs by inhalation - ie showers . Robert

[Doctor Drivel]

"robgraham" wrote in message news: [e-mail]... I posted a query some time back about the advisability of having a heatbank set up with a TMV to control the DHW to something like 50C as suggested in the DIYWiki. My concern was that distributing water at this temperature could be a spawning ground for legionella but was querying if anyone knew anything about this - there was no answer !!

[Doctor Drivel]

http://64.233.183.104/search?q=cache:Hxt0SQsRsXIJ:

He could have contracted that in he hotel he was kin and it came out in his second home, with the home having nothing to do with it. He is assuming.

[Timothy Murphy]

http://64.233.183.104/search?q=cache:Hxt0SQsRsXIJ:

>>

I didn't think it was completely obvious that he had had Legionella. As I understood the story (which I didn't read very carefully) he had pneumonia, and after this was cured he showed immunity to Legionella.

According to my reading, 15% (IIRC) of the US population show this immunity, so it would not be clear that he had just had the disease, which is a kind of pneumonia, as I understand it. His symptoms did not seem to follow those of Legionella, eg he felt ill immediately after taking a shower, while Legionella is said to take a minimum of 2 days to take effect.

[Doctor Drivel]

http://64.233.183.104/search?q=cache:Hxt0SQsRsXIJ:

>>>>>> He could have contracted that in he hotel he was kin and it came out in >> his

That is why I assumed the hotel was the place.

[Onetap]

They give the information for the time taken to kill legionella. They don't give the time taken for the bacteria to, say, double, because it also depends on the nutrients (limescale, tallow, leather washers, hemp; vegetable, animal or insect remains from unhygenic cold water storage tanks, etc..).

The time can be misleading. 60 degC wil kill the bacteria, but it usually manages to survive under limescale accumulations in the bottom (coolest bit) of water storage cylinders, or under bio-films on uninsulated pipework. It then re-infests the system.

[Onetap]

He was slightly ill before he got in the shower. It doesn't say how long after his shower that he was diagnosed with legionellosis.

It follows the established pattern; compromised immune system (NHS hospital patients, elderly American legion veterans); stagnant, tepid water; inhalation of an atomized of water spray. The shower remains the prime suspect, IMHO. You could pretty much guarantee it was heavily colonized.

It might have been the hotel. I'd be surprised, commercial maintenance standards are usually higher, given the threat of litigation.

[Pete C]

Looking around it appears a Canadian study points the finger at electric water heaters:

An Italian study seems to clear them:

water system wouldn't make much difference, it's down to the type of water heater and how it's used.

Instead of partially heating a big hot water cylinder, maybe it's best to have... two hot water cylinders! :)

cheers, Pete.

[Andy Hall]

No, it's two combis.

[Doctor Drivel]

Matt, you do surprise me, as you are actually learning.