"Ed Pawlowski" wrote in message
...
On 8/7/2015 6:29 PM, Ashton Crusher wrote:
speaking of muck, I've had far far less muck form by turning the
temperature down below "normal" on the dial. I keep it around 120
degrees or less and it seems to reduce the formation of muck and crud.
Less than 120 is a good range for legionella though. I opt for 130 for
safety.
NIH has some differing views but you can find lots of others:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC118082/
L. pneumophila multiplies at temperatures between 25 and 42°C, with an
optimal growth temperature of 35°C
That's 77F to 107.6F with an optimal growth temperature of 95F.
Legionella pneumophila (203). Legionellae are intracellular parasites of
freshwater protozoa and use a similar mechanism to multiply within mammalian
cells (91). These bacteria cause respiratory disease in humans when a
susceptible host inhales aerosolized water containing the bacteria or
aspirates water containing the bacteria. Again:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC118082/
The key to infection is "inhaling aersolized" water or actually aspirating
water into the lungs. My understanding is that it grows best in the
condensate of rooftoop cooling towers and not in water heaters:
During the past 3 years, the epidemiology of Legionnaires' disease has
been dominated by the occurrence of several large outbreaks, two linked to
cooling towers and one linked to a whirlpool spa. In April 2000, a large
outbreak of Legionnaires' disease occurred among persons visiting the newly
constructed aquarium in Melbourne, Australia (9). By June, 119 persons were
confirmed to have Legionnaires' disease, and four (3.6%) persons died. This
outbreak was due to a new cooling tower which had recently come on line. It
demonstrated that even new cooling tower systems pose a risk when coming on
line and that decontamination procedures should be followed.
And yes, I realize hotter water is better in the case of killing
Legionnaire's bacteria but the tradeoffs are a greater chance of scalding.
That said, OSHA says this:
https://www.osha.gov/dts/osta/otm/legionnaires/faq.html
Q. Can my home water heater also be a source of LDB contamination?
A. Yes, but evidence indicates that smaller water systems such as those used
in homes are not as likely to be infected with LDB as larger systems in
workplaces and public buildings.
One of the reasons it thrives in cooling towers is that it prefers warm,
stagnant water with a source of food. A cooling tower is pretty much the
ideal growth medium because bugs, bird droppings and all sorts of nasty food
for bacteria live there. The first diagnosed outbreak that gave the bug its
name was found in the Legionnaire's hotel cooling tower.
Q. Do you recommend that I operate my home water heater at 60°C (140°F)?
A. Probably not if you have small children or infirm elderly persons who
could be at serious risk of being scalded by the hot water. However, if you
have people living with you who are at high risk of contracting the disease,
then operating the water heater at a minimum temperature of 60°C (140°F) is
probably a good idea. Consider installing a scald-prevention device.
Those most likely at risk probably should amp up the temperature of their
water heater:
a.. Organ transplants (kidney, heart, etc.)
b.. Age (older persons are more
likely to get disease)
c.. Heavy smoking
d.. Weakened immune system (cancer patients, HIV-infected individuals)
e.. Underlying medical problem (respiratory disease, diabetes, cancer,
renal dialysis, etc.)
f.. Certain drug therapies (corticosteroids)
g.. Heavy consumption of alcoholic beverages
Since I am not in the high risk category and the water in my 120F water
heater doesn't have much of a chance to get stagnant, I don't worry about
it. Too much. Many other nastier demons out there.
Here's something really nasty that can be found in warm freshwater.
http://www.webmd.com/brain/brain-eating-amoeba
The so-called brain-eating amoeba is a species discovered in 1965. It's
formal name is Naegleria fowleri. Although first identified in Australia,
this amoeba is believed to have evolved in the U.S.
There are several species of Naegleria but only the fowleri species causes
human disease. There are several fowleri subtypes. All are believed equally
dangerous.
N. fowleri is microscopic: 8 micrometers to 15 micrometers in size,
depending on its life stage and environment. By comparison, a hair is 40 to
50 micrometers wide.
Like other amoebas, Naegleria reproduces by cell division. When conditions
aren't right, the amoebas become inactive cysts. When conditions are
favorable, the cysts turn into trophozoites -- the feeding form of the
amoeba.
Naegleria loves very warm water. It can survive in water as hot as 113
degrees Fahrenheit.
These amoebas can be found in warm places around the globe. N. fowleri is
found in:
a.. Warm lakes, ponds, and rock pits
b.. Mud puddles
c.. Warm, slow-flowing rivers, especially those with low water levels
d.. Untreated swimming pools and spas
e.. Untreated well water or untreated municipal water
f.. Hot springs and other geothermal water sources
g.. Thermally polluted water, such as runoff from power plants
h.. Aquariums
i.. Soil, including indoor dust
Naegleria can't live in salt water. It can't survive in properly treated
swimming pools or in properly treated municipal water.
Most cases of N. fowleri disease occur in Southern or Southwestern states.
Over half of all infections have been in Florida and Texas.
As for scalding v. Legionnaire's, there are apparently 10K to 50K cases a
year of LD compared to 500K for scaldings. That makes the risk from hot
water burns far more likely than catching Legionnaire's. I think the
increased longevity of the heater and the lessening of the scald risk are
well worth turning the dial back. Saves money, too. YMMV
Over 500,000 scald burns occur annually in the United States.
The two highest risk populations are children under the age of 5 and adults
over 65.
Did you know…
a.. Hot liquids can cause life-threatening burn injuries.
b.. Scalds are the number-one cause of burn injury to children under age
4.
c.. Burn accidents frequently occur when parents or caregivers are in a
hurry, angry, or under a lot of pressure.
d.. Coffee, tea, soup and hot tap water can be hot enough to cause serious
burn injury.
e.. Scald and steam burns are often associated with microwave oven use. *
f.. When tap water reaches 140º F, it can cause a third degree (full
thickness) burn in just five seconds.
g.. Hot tap water accounts for 17% of all childhood scald
hospitalizations.
http://www.burnfoundation.org/progra...ce.cfm?c=1&a=3
*Ever heat water in a coffee mug and have it boil over just as you open the
door? It's very nasty and I assume that it's the same sort of phenomenon
where water can freeze over in seconds if it's supercooled and it's
disturbed by a loud noise.
https://en.wikipedia.org/wiki/Supercooling
Droplets of supercooled water often exist in stratiform and cumulus
clouds. Aircraft flying through these clouds see an abrupt crystallization
of these droplets, which can result in the formation of ice on the
aircraft's wings or blockage of its instruments and probes, unless the
aircraft are equipped with an appropriate de-icing system. Freezing rain is
also caused by supercooled droplets.
IIRC (and these days mostly I don't) the Air France flight that crashed in
the Atlantic Ocean a few years ago had a pitot tube speed sensor (actually
3) whose internal heaters were all overwhelmed by supercooled water.
https://en.wikipedia.org/wiki/Superheating
Aha! The site above finally explains why the coffee mug sometimes "spits
up" all over the inside of the microwave (but fortunately not my face)
Superheating is an exception to this simple rule; a liquid is sometimes
observed not to boil even though its vapor pressure does exceed the ambient
pressure. The cause is an additional force, the surface tension, which
suppresses the growth of bubbles.
Surface tension makes the bubble act like a rubber balloon (more precisely,
one that is under-inflated so that the rubber is still elastic). The
pressure inside is raised slightly by the "skin" attempting to contract. For
the bubble to expand, the temperature must be raised slightly above the
boiling point to generate enough vapor pressure.
What makes superheating so explosive is that a larger bubble is easier to
inflate than a small one; just as when blowing up a balloon, the hardest
part is getting started. It turns out the excess pressure due to surface
tension is inversely proportional to the diameter of the bubble.
Another mystery revealed by Google and Wiki. (-:
--
Bobby G.