How Does Chlorine Safely React w/ Ammonia in a Pool?

saint_malachy

Active member
Jun 27, 2009
30
This is a bit off topic, but I am curious about this as mixing bleach and ammonia outside of water probably kills hundreds of people each year. How do they safely react within a pool? Is it just the levels of both are so low?
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
Yes, concentration is everything. The most irritating by-product in the reaction of chlorine with ammonia is nitrogen trichloride which is very volatile as well. The amount of nitrogen trichloride that is produced is proportional to the chlorine concentration, assuming there is an excess of chlorine relative to ammonia (which is usually the case). Technical details about this are here.

The Cyanuric Acid (CYA) in pool water makes the effective active chlorine (hypochlorous acid) concentration very low -- roughly equivalent to around 0.1 ppm Free Chlorine (FC) if there were no CYA. So the amount of nitrogen trichloride produced under these conditions is exceptionally low. The concentration of 6% bleach is around 60,000 ppm or over 600,000 times higher. The concentration of ammonia in typical industrial or household accidents mixing chlorine with ammonia is also far higher than found in pools.

Richard
 

Pontiac

In The Industry
Aug 30, 2009
30
Northern CA
chem geek said:
The most irritating by-product in the reaction of chlorine with ammonia is nitrogen trichloride which is very volatile as well. The amount of nitrogen trichloride that is produced is proportional to the chlorine concentration, assuming there is an excess of chlorine relative to ammonia (which is usually the case).


Great website!
You guys are way ahead of the curve. You even leave most of the pool industry in the dust.

I have a question that I have always wondered about and I think relates to this subject.

I know of a few instances where bathers have developed rashes from using their spa. These were in ground pool/spa gunite swimming pools. The rashes always occurred in the spa, never in the pool. My theory is that large amounts of urea (in the confined area of the spa), converted the existing high levels of chlorine into monochloramine causing the irritation on the skin. Furthermore, since most spas are heated, the bather's skin pours are more open and susceptive.

Could you elaborate on this a little bit more?

Thanks!
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
Based on reports on spa forums I've seen, most rashes in spas are due to skin irritation from the jets or from people who have a skin condition that is sensitive to hot water. These rashes show up within 24 hours and get worse with additional exposure. Another source of rash is from the Pseudomonas aeruginosa bacteria, aka "hot tub rash/itch" though this usually shows up after 24 hours and doesn't get worse from additional exposure to the spa and is most commonly caused by too low a sanitizer level.

It is, of course, possible for some people to be irritated by monochloramine and you are correct that in spas due to the high bather load (bathers per water volume) and high temperatures (so more sweat) that there is far higher exposure to monochloramine, but there is only anecdotal evidence of a small number of people affected (see this and this for differing viewpoints of monochloramine in tap water used for showering).
 

Pontiac

In The Industry
Aug 30, 2009
30
Northern CA
Thanks for your take on the subject. I will have to add "jets" to my list. Of all the rashes I have personally known about, and after further investigation, urine was introduced into the spa.
 

Water_man

LifeTime Supporter
Jun 7, 2008
390
Brookline, MA
chem geek said:
Another source of rash is from the Pseudomonas aeruginosa bacteria, aka "hot tub rash/itch" though this usually shows up after 24 hours and doesn't get worse from additional exposure to the spa and is most commonly caused by too low a sanitizer level.
Does this rash/itch-causing bacteria, or similar ones, also reside in swimming pools with normal santizer levels?