 |
 |
|
 |
 |
 |
 |
 |
 |
 |
 |
| |
REPP-CREST
1612 K Street, NW
Suite 202
Washington, DC 20006
contact us
|
|
 |
|
|
|
|
| Greenbuilding Archive for March 2001 |
|
| 257 messages, last added Tue Nov 26 17:25:09 2002 |
[Date Index][Thread Index]
[GBlist] Re: Legionella is your Home - heat your water properly
Sgrìobh John Herbert:
>Sessile - the ones that stick inside the biofilm and given the right
>habitat 33-45 deg C grow to large numbers. (The temperature band for
>optimum growth depends on the study you read but are broadly the
>same)
>
>So taking a single bacteria, it may floating thro' your system and
>exit (small risk to user) or may start a colony in any convenient
>biofilm. Later a high conc. are released into the water (high risk).
But according to all the materials I've read, which now include
the papers you cite below, large-scale reproduction doesn't occur
until you're within that particular temperature range.
>Your argument (position) about the _time_ would lead one to think
>that Legionella just flies thou your water system which is not the
>case.
I understand that a sessile colony can put out lots of progeny
under the right circumstances, and that the probability of infection
rises with the number of bacteria one is exposed to. However, that
large-scale reproduction can't happen if you're not in that optimal
temperature range, right?
> >Neither does vaguely asserting that one is an expert.
>
>Of course, and your entitled to your opinion, but my point was only
>that other readers, may believe that your assertions are fact.
I understood. My point was that you were making assertions
without enabling us to evaluate them, either by providing source
material or explaining the extent of your personal or professional
knowledge.
I would be interested to know how you came to know so much about
Legionella. Are you a doctor, a builder, a consultant, some other
kind of professional, a knowledgeable enthusiast, or what?
> > Okay. Up to that point in my explanation, I was talking about a
>> demand hot water system with no standing hot water, which gets
>> flushed several times daily with fresh well water, from a well which
>> gets chlorinated at least annually. I hadn't even gotten to
>> recirculation at that point. You're telling me that there's a
>> significant risk from cold water which gets heated once to 52°C and
>> then used immediately? I'd like to know why.
>
>1. A "floater" may pass straight thou your system no problem.
>However, some bacteria form sessile populations that subject to the
>temperature, PH, nutrition and iron content form large numbers
>inside an amebae. Then, at some point, large numbers of bacterium
>are released into the your system.
When I turn the heater on, cold water becomes hot and a few
seconds later it flows out of the tap. In those few seconds, there
will be no significant bacterial reproduction. So if there's a large
colony of Legionella in the system, it had to breed in the cold
water, prior to the heater. So what I hear you telling me is that
these sessile populations will produce these large numbers, even in
cold water (below 20°F). Is that right? If so, it's contrary to
what I've found in the literature, including what you referred me to.
>2. Chlorination, at "normal" levels 1-5 ppm does not kill
>Legionella, that is why Legionella can pass thou municipal water
>treatment systems into your home.
>
>You have a well, but you didn't mention the annual dosage, is it
>"shocked" annually?
Yes. Actually, I shock the well every time I work on the
plumbing, so to date it gets shocked about three times a year as I
add to the system. Once we're done, though, it'll be an annual
ritual. Actually, I over-did it the first two times as I was trying
to get the right dosage, so "bombed" might be a better description
for the first two hits.
>HSE - UK
>They state para 10....."This is the traditional approach. It is
>recommended that hot water should be stored at 60°C and distributed
>so that, after one minute of running, a temperature of at least 50°C
>is attainable at outlets. Cold water storage and distribution should
>be at 20°C or below"
>from:
>http://www.hse.gov.uk/pubns/misc150.pdf
>************************************************
My cold water storage and distribution is under 20°C, so we're
all set there. My hot water storage is nonexistent. There's no hot
water stored in the system. The hot water lines do sometimes have
hot water running from heater to tap, but then they cool down to the
ambient temperature again, which is under 20°C except during summer,
and even then under 25°C. And, they all get flushed regularly during
daily use.
I ran across several other sources while I was searching for the
news report and the Canadian utility study which you alluded to. One
puts the lower safety limit at 25°C.
(http://www.ashrae.org/ABOUT/leg_papr.htm) Except when actually
running hot water and for a short time afterward, my entire system is
below 25°C at all times, and that includes the radiant heat loop.
>Ashrae - USA
>They state para. 4.1.6....."hot water stored above 60 deg C".......
>from:
>http://www.baltaircoil.com/pdf/guideline12-2000.pdf
>************************************************
Don't stop there. Let's quote from that one a little more extensively:
---
"4.1.6. Recommended Treatment. Where practical in health care
facilities, nursing homes, and other high-risk situations, cold water
should be stored and distributed at temperatures below 20°C (68°F),
while hot water should be stored above 60°C (140°F) and circulated
with a minimum return temperature of 51°C (124°F). However, great
care should be taken to avoid scalding problems...
"Where practical in other situations, hot water should be stored at
temperatures of 49°C (120°F) or above."
"For potable water systems that were opened for repair or other
construction or systems that were subjected to water pressure changes
associated with construction (which may cause water to become brown
and the concentration of Legionella to dramatically increase), [34]
it is recommended that as a minimum the system be thoroughly flushed."
---
I must say that I wasn't impressed with ASHRAE 12-2000. It tells
you that in non-high-risk situations it's okay to *store* water at
49°C, which is outside the "danger" zone, but well inside the zone
which will support Legionella reproduction, according to every other
source. 49° is even lower than most people set their hot water tanks.
I note, however, that they're all talking about water *storage*.
I'm not *storing* hot water. I'm storing cold water, and then
heating it as necessary and using it immediately. I don't think the
cases are parallel.
>Do we have a worldwide conspiracy?
They're all reasonably consistent, but I don't hear them saying
what I hear you saying. Perhaps your point would be clearer if you
read over the description of my system and pointed out exactly where
Legionella can breed, and why. I've gone to the time and the trouble
to read your citations thoroughly, think about them, and reply to
you, but I'm starting to conclude pretty firmly that you didn't
bother to read my description and think it through. I think that it
would make your argument much more credible if you did that.
>One can always pick one bone of contention to try and disprove
>research, but do you believe that:
>
>***************************
>CDC - USA
>http://www.cdc.gov/ncidod/dbmd/diseaseinfo/legionellosis_t.htm
>*************************************************
Do I believe what, exactly? I read the CDC's information, and it
seems to be in accord with what everyone else says about Legionella.
>-----------------------------------------------------------
>A CBS report:
>Dan Rathers report 15.12.2000
>
>.......One patient who wasn't initially tested was 70-year-old
>Ernest Gresko, whose death from Legionnaires' disease three years
>ago fit an alarming pattern......
>
>source from
>www.cbsnews.com
I went to http://www.cbsnews.com/ and used their search function,
looking for "Legionnaires", "Legionnaires'", and "Ernest Gresko", but
I could not find the article you are quoting. You were kind enough
to send me the text on request, which I won't quote here in full,
since it's typical newspaper fluff and doesn't add anything to the
science. It does tell us about deaths from Legionella, but that such
deaths happen isn't a point in dispute.
> > >FACT: 25% of domestic/residential systems are infected
> >
> > Source?
>
>This was reported by a Canadian utility company (I cant remember
>that reference right now) but a search on the net should reveal the
>study. Whether the study covered tankless water-heaters or not I
>don't recall, but if you read further you will understand why that
>point is not important.
I couldn't find that one either, though I did find and read a lot
of other material, which pretty much covered the information you
refer to above.
> > >Millions of dollars in research by leading institutions concluded
>> >heat water to above 60
>>
>> Millions of dollars in research have told us that current
>> forestry practices are sustainable, too, but it turns out that they
>> aren't.
>
>Personally, I never believed that the so called "sustainable"
>forestry practices (funded by logging companies?) were true, did you?
Nope. I was trying to make a point by constructing a parallel
argument which was clearly false. Rather than attempt another
analogy, I'll lay it out straight: the millions of dollars don't
mean anything if they weren't spent studying a situation relevant to
the situation at hand.
I'm looking forward to hearing your thoughts on the system I described.
Best wishes,
-Speireag.
--
Speireag Alden, aka Joshua Macdonald Alden
...the last word in ignorance is the man who says of an animal or
plant: 'What good is it?' --Aldo Leopold, _A Sand County Almanac_
______________________________________________________________________
This greenbuilding dialogue is sponsored by REPP/CREST, creator of
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
______________________________________________________________________
|
|
|
