|02-28-16, 01:03 PM
Join Date: Mar 2014
Location: Florissant, Colorado
Thanked 59 Times in 55 Posts
More info on Legionella:
MMT, Please note that I have removed many references that "bad mouth" Open or Combined systems.
I agree with you, that either type of system, closed or open can be very dangerous if the water is allowed to stagnate.
Here are some selected quotes from hydronic heating experts on this topic:
"The CDC estimates that upwards of 10,000 people die from community acquired Legionnaires each year. They also tag water heaters and potable hot water distribution systems as amplifiers."
"the aspiration of small sized water droplets into the lower 1/3 of the lungs that represents the pathway for Legionella bacteria.
Drinking legionella does not pose a known risk, although the same can't be said for many other water borne pathogens.
Showering is often thought to be the only distal site within the home, but faucet areators and flushing a water closet also emit micron-sized water droplets.
Amplification of Legionella becomes a concern with water temperatures below 133F. If you couple up the other favorable growth issues (stagnation, pH and biofilms), you've managed to create a perfect hydroponic bacteria growing amplifier. "
"First point: Non-reported cases. As I understand it, the CDC only addresses outbreaks of Legionella. Events where many people are affected... they are focused on epidemics, not isolated incidents that may occur in individual homes.
Second point: Misdiagnosed cases. Bacterial pneumonia kills a LOT of people in the U.S. every year. No-one knows how many of these cases may have been Legionella.
Third point: Healthy people aren't likely to get LD unless exposed to massive amounts of the bacteria. Our immune systems are generally able to handle it quite well. Grandma isn't so lucky, especially not if she smokes. Cancer suppressing drugs can also weaken the immune system. The Legionaires - old guys that smoked and happened to be near a cooling tower. Outbreaks in hospitals - weakened immune systems.
A healthy person CAN get it if the bacteria are present in numbers sufficient to overwhelm the immune system, as in cooling towers."
"reality is ....
I won't live long enough to see our code bodies enact this common sense solution that addresses both scalding and bacterial issues. Politics at the code enacting level is fierce and intense. One code official I spoke with likened it to turning a battleship in heavy seas using only a trolling motor.
Min tank temperature of 140 F (source). Distribution systems temp min of 133 F with constant circulation (distribution). All points of use with final step-down of temps via certified scald-guard devices (points of use)."
"Chlorine is ineffective against Legionella bacteria at concentrations found within potable water systems. If chlorine levels are raised to a point where it can begin to kill off the bacteria, the water becomes far too agressive for metal or plastic piping and combines with organic materials to form carcinogens.
Furthermore, as water is heated chlorine dissipates. That's one reason why we see more pitting in the hot water piping.
Pasteurization of hot water is quite effective for keeping the bacteria numbers suppressed if the water temp is held above 133 F with a contact time of at least 20 minutes.
So much for the storage tank or source of hot water. Let's call that part #1 of a 3-piece puzzle. Part #2 is the distribution system or maze of piping. Part #3 of the system are the points of use (faucets).
If we are to have bacterial safety within the potable hot water system, all three must be treated.
Here's how that could work. Elevate the storage tank's temperature to 140 F minimum.
Install a certified ASSE 1017 thermostatic mixing valve at the tank's outlet and set it for 133 F.
Install a bronze circulatory to move water through the distribution system 24/7.
Part #3 of the puzzle comes next but we've got to bring scalding safety into the picture due to the elevated temperatures (which we had anyway as the current Z21.10.1 regulations allow for water temps of up to 190 F from stacking in residential water heaters of 75 gallons or less). We'll need to add certified ASSE 1016 scald guard faucets or devices at points of use where human contact occurs.
106 F is the human threshold for pain. 120 F, the current mantra for so-called safe water temps - is not. Third degree burns are still a reality and thousands of people continue to be scalded annually. If the delivery temp is limited to 110 F, actual safety for bathers begins. That's why old folks homes are limited to 105 - 110 F. But that's also why most test positive for Legionella bacteria.
There are three types of certified ASSE 1016 valves: pressure balancing; thermostatic; and the best of the three - thermostatic combined with pressure balancing. Pressure balancing valves are blind to seasonal temperature fluctuations (incoming water service temps can vary by as much as 50 F between winter and summer - also, if the homeowner runs out of hot water, their first reaction is to turn up the tank's thermostat, which changes the PB faucet's upper limit - who's to know?).
Scald guard faucets are readily available and if the codes would change to this new "standard", plumbing inspectors would be required to verify proper setting was performed by the installer. Safe hot water systems, safe bather temperatures and reduced liability for the water heater manufacturers, the plumbers and others involved (such as the supply houses)."
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Mobile Master Tech (03-01-16)
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