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Thread: How much chlorine is too much?

  1. #1
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    How much chlorine is too much?

    I am trying to find data on how much chlorine is too much or unhealthy. That is, at what point do the harmful effects of chlorine out weigh the benefits of the chlorine's ability to disinfect? I am a regulator for a local health department, and as such I do not have a single pool that I care for (though I see about 180 pools each year). That said, I am aware that other chemicals may make a difference so please assume the following:
    pH-7.4
    Total Alkalinity- 130
    I would like numbers (if they change) for CYA at 0,30,50,and 80ppm.
    Anecdotal data is nice, but if you can post links to research, that would be great as I may need it to show the State Health department. Thank you all for your help, and I am sorry if this is posted in the wrong forum.
    Local Health Department Public Pool Inspector.
    Review NEW public pool (4 or more living units) plans
    Inspect around 180pools or spas annually
    Most are in-ground Plaster, a few fiberglass, No above ground pools and only 1 or 2 spas.
    Charged with enforcing http://www.rules.utah.gov/publicat/c...2/r392-302.htm
    Use a Palintest Pooltest 9 Premier for most chemical tests

  2. #2
    Mod Squad JohnT's Avatar
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    Re: How much chlorine is too much?

    Welcome to TFP!

    I'd think Chem Geek would be the guy to talk to. I'll PM him and ask him to look at this post.
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  3. #3
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    Re: How much chlorine is too much?

    There's the law and regulations and then there is reality. I'll give you a bit of both since the regs have not kept up with the latest science (and by latest, I mean as far back as 1974!).

    First off, there are no national regulations or laws regarding chlorine amounts in pools or spas. Such regulations are at the state or county (i.e. associated with health departments) or sometimes the city level. However, the EPA does have a maximum chlorine level specified for drinking water as listed in their Drinking Water Contaminants webpage where they list a maximum chlorine level of 4 ppm. This post gives a few limits for some states and you will see that some exceed the 4 ppm EPA limit with the highest being 10 ppm in Florida. The EPA also regulates (via FIFRA) what can be written on pesticide product labels with regard to pathogen kill claims and dosages. So chlorine products will never say more than 4 ppm FC for pools.

    One of the big problems is that current regulations look only at the Free Chlorine (FC) level by itself and not in conjunction with Cyanuric Acid (CYA). Separate limits are set for each. This is idiotic since the FC alone is irrelevant when it comes to reaction rates for disinfection, oxidation, corrosion, creation of disinfection by-products, etc. The FC level in isolation is only relevant from a capacity point-of-view so is relevant for drinking water, not swimming in it. Also, some people assume that the lower disinfection rates when CYA is present is always a problem rather than seeing that the higher active chlorine level without CYA is perhaps a bigger problem. Fortunately, it takes a very low active chlorine level to kill most pathogens and for those that are highly chlorine-resistant such as the protozoan oocyst Cryptosporidium parvum, one can use supplemental systems such as ozone, UV, AOX or even overnight chlorine dioxide. To minimize the oxidation of skin, hair, swimsuits, corrosion of equipment, and rate of creation of disinfection by-products, I think that a reasonable target for commercial/public pools and spas is an FC that is around 20% of the CYA level so indoors that would be 4 ppm FC with 20 ppm CYA or 6 ppm FC with 30 ppm CYA while outdoors perhaps one could go lower if exposed to UV in sunlight so perhaps as low as an FC that is 10% of the CYA level so 5 ppm FC with up to 50 ppm CYA. For residential pools and spas, there are no regs, but if there were they should be looser and closer to the algae-growth prevention limits in the 5-7.5% FC of CYA range. The FC that is 20% of the CYA level (at 77F) is roughly equivalent in active chlorine concentration to 0.2 ppm FC with no CYA.

    Are you asking about this due to the CDC MAHC's Disinfection and Water Quality Code and Disinfection and Water Quality Annex where they are proposing to ban CYA completely from indoor venues, spas and "increased risk venues" such as waterparks and whirlpool baths? You realize that public comment for this is now closed. I sent extensive comments about this to CDC MAHC. You can read more about this issue in the Pool & Spa News "New Code Proposes CYA Restriction" article where you can also read some of my comments there (you'll also see that Bob Lowry has comments similar to some of my posts since I had been in contact with him previously, but he doesn't link to or refer to the sources). My take on the CDC MAHC proposals (as they currently stand) is that they are as biased in the direction of "more is better" for active chlorine and "CYA is bad so should be avoided" than the APSP-11 recommendations were in the direction of "CYA doesn't matter". The CDC MAHC is being driven by fear of Crypto outbreaks and pathogen control without regard to disinfection by-products or other side effects of high active chlorine levels while the APSP-11 was driven by chlorinated isocyanurate manufacturer desires for continued sale of their products. I'm oversimplifying, of course, since there were a lot of good science references written in APSP-11, but it was largely ignored when it came to setting FC and CYA levels. Ironically, the CDC MAHC also refers to peer-reviewed papers, but ignores whole categories they'd rather not deal with. Neither group looked at the raw fundamental and very basic science regarding the chlorine/CYA relationship and how CYA moderation of chlorine's strength can be seen as a good thing if done in moderation.

    You can see from other CDC MAHC modules that my comments are largely being ignored in 1.0, 2.0, 3.0 Preface, User Guide and 6.1 Operator Training Module, but I am still hopeful that the Disinfection and Water Quality Committee will take my comments more seriously.
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    Re: How much chlorine is too much?

    Thanks for you time Chem Geek.

    I am Not asking because of the MAHC (I mostly think that is a disaster waiting to happen at this point, After VGBA I don't want the feds to touch pool rules ever again)

    The reason I ask is that my state has minimums set for free chlorine (both for Stabilized and Non-Stabilized) that can be found in Table 6 here http://www.rules.utah.gov/publicat/code ... 92-302.htm ; but there are no maximum levels in the table. Common sense tells be that there has to be a point at which the Chlorine in the water becomes unhealthy and/or unsafe for the swimmer, but I am struggling to find any research to support that hypothesis. The EPA standard is a great starting point, that I had not found yet, but at the same time, as a regulator, I don't WANT people drinking the pool water.

    Do you have any research to point to to support the 20% of stabilizer Idea, I may be able to get the state to consider something like that.And could you please expound on this statement "higher active chlorine level without CYA is perhaps a bigger problem"

    As to the MHAC banning CYA, They are over shooting. What I see inspecting pools is extremely high CYA (150ppm +) on all pools that use Tab feeders, regardless of if they are indoor or outdoor. The pools that use salt or liquid chlorine and manually add CYA almost never have any problems.
    Local Health Department Public Pool Inspector.
    Review NEW public pool (4 or more living units) plans
    Inspect around 180pools or spas annually
    Most are in-ground Plaster, a few fiberglass, No above ground pools and only 1 or 2 spas.
    Charged with enforcing http://www.rules.utah.gov/publicat/c...2/r392-302.htm
    Use a Palintest Pooltest 9 Premier for most chemical tests

  5. #5
    Mod Squad jblizzle's Avatar
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    Re: How much chlorine is too much?

    Wow, there are a few things in Table 6 that counter recommendations here:

    One is the minimum of a Calcium Hardness of 200ppm ... for a vinyl pool it does not matter and some keep theirs down closer to 50ppm.
    Same with the TA ... often we try to get down to 50ppm or so with SWG to hold the pH down.
    The minimum FC for stabilized pools is just off as it does not take into account the CYA level ... the minimum could be 7ppm for CYA of 100ppm (this was discussed above I believe)

    This is some interesting stuff.
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  6. #6
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    Re: How much chlorine is too much?

    Yes, I agree that you really shouldn't have such high TA level requirements when hypochlorite sources of chlorine (or saltwater chlorine generators) are used. A higher TA level is only needed when using Trichlor because it is so acidic. By having the TA be required to be a minimum of 80 ppm, then some pools using hypochlorite or SWCGs and especially those with more aeration are going to be having a lot of acid added to them unnecessarily. The pH of such pools could be made much more stable by allowing for a lower TA level.

    Anyway, back to the FC maximum. If there is CYA in the water, then the active chlorine level is very low so a "safe" maximum could be very high. Note the following from the EPA in this link with regard to drinking high FC levels of chlorine (with no CYA):

    No adverse effects were noted in persons ingesting water containing 50-90 ppm of chlorine (~1.4 to 2.6 mg Cl/kg/day) for a short periods of time (U.S. EPA 1989). Drinking water concentrations of >90 ppm chlorine caused irritation of membranes of throat and mouth (U.S. EPA 1989). Concentrations of chlorine in the drinking water of greater than 25 ppm make the drinking water unpalatable (U.S. EPA 1989).
    Even the irritation effects wouldn't likely occur if there is CYA in the water because those effects are a function of reaction rates which are slow when CYA is present (i.e. when the FC/CYA ratio isn't high).

    For practical purposes, when there is CYA in the water there isn't really an FC maximum that makes sense. If there were 200 ppm CYA, then even 100 ppm FC wouldn't be a problem, but in practice you don't need an FC higher than 20% of the CYA level for decent disinfection rates in commercial/public pools. If you wanted to set a maximum FC of 20 ppm when CYA is present, that would be reasonable. 10 ppm might be a problem if you allow CYA to get to 100 ppm as you do currently since having less than 20 ppm FC with 100 ppm CYA would have the disinfection and oxidation rates drop lower than one would normally want in a commercial/public pool. I suppose if it's an outdoor pool exposed to sunlight, then getting down to 10% of the CYA level so 10 ppm FC with 100 ppm CYA is OK but I wouldn't go lower than that. Technically, your minimum and maximum limits should be an FC level relative to the CYA level (when CYA is present) and not separate limits for FC and CYA. A broad range would be a minimum FC that is 5% of the CYA level and a maximum FC that is 30% of the CYA level though in practice for commercial/public pools staying in the 10-20% range makes more sense IMHO.

    As for not having CYA, then the FC maximum would be more like the EPA limit of 4 ppm though really not having any CYA in the water at all has the chlorine be stronger than it needs to be by an order of magnitude or more.

    Remember that what I am describing with regard to setting a target based on the FC/CYA ratio is not being done anywhere in the country even though it's based on sound science as well as the experience of tens of thousands of pool owners (though their FC/CYA ratios are lower at 5-15%). Take a look at the "Chlorine/CYA Relationship" section in the Certified Pool Operator -- What is not taught thread including its links to numerous peer-reviewed scientific papers in respected journals.

    When I wrote that "higher active chlorine level without CYA is perhaps a bigger problem", I am referring to the fact that an FC with no CYA at usual levels of at least 1-2 ppm results in faster oxidation of skin, swimsuits and hair and faster corrosion of equipment and faster creation of disinfection by-products (and a greater amount of them, assuming you have other means for removing organic precursors and intermediates such as using ozone or UV). In Europe, DIN 19643 has a target FC range of 0.3 - 0.6 ppm with no ozonator or 0.2 - 0.5 ppm with an ozonator and the reason for such low FC levels is to reduce these side effects, especially disinfection by-products. However, it can be impractical to try and maintain such low FC levels which is why I propose using CYA since it acts as an active chlorine buffer letting you have an ample reserve of chlorine (i.e. FC level) while simultaneously having a reasonably low active chlorine level (roughly half the FC/CYA ratio). You get the best of both worlds -- a higher FC so you don't "run out" of chlorine, even locally, while having the active chlorine level be low to reduce the rate of disinfection by-products and other side effects of chlorine.
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  7. #7
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    Re: How much chlorine is too much?

    Chem Geek, Thank you so much, I think this may be immensely helpful. I should be able to use at least some of the information you provided, at the very least to educate operators in my area.

    JB, Most vinyl pools are prohibited from use as a public pool by rule in Utah.
    Local Health Department Public Pool Inspector.
    Review NEW public pool (4 or more living units) plans
    Inspect around 180pools or spas annually
    Most are in-ground Plaster, a few fiberglass, No above ground pools and only 1 or 2 spas.
    Charged with enforcing http://www.rules.utah.gov/publicat/c...2/r392-302.htm
    Use a Palintest Pooltest 9 Premier for most chemical tests

  8. #8
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    Re: How much chlorine is too much?

    Quote Originally Posted by Ricochet
    Most vinyl pools are prohibited from use as a public pool by rule in Utah.
    Why's that? Just curious. I'm also curious why you seem to not like the VGBA? Having a regulator's perspective is interesting; I'm glad you're here
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  9. #9
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    Re: How much chlorine is too much?

    Quote Originally Posted by Melt In The Sun
    Why's that? Just curious. I'm also curious why you seem to not like the VGBA? Having a regulator's perspective is interesting; I'm glad you're here
    There is a LOT of law that has not kept up with current technology, I think that the prohibition against public pool being vinyl is at least partially influenced by this. You can see http://www.rules.utah.gov/publicat/code ... 92-302.htm for details about what is allowed and what is not. Another issue is durability and maintenance combined with the fact that the law tries to address the lowest common denominator. The up side is that the current trend in new laws seems to be toward more performance rather than prescriptive based standards.

    As to VGBA my problem there is mostly federal interference in to local matters but here is a break down of my thoughts
    1-Cramming Development of new tech and retrofitting all pools in to a one year time frame was just asking for trouble (as evidenced by the recent drain cover re-call) Pools that acted quickly to comply ended up spending WAY more than those that dragged their feet, and often the work was not properly done the first time.
    2-The CPSC doesn't seem to be able to make up their minds about certain aspects of the law and the guidelines keep changing. (like what un-blockable means) they seem to be WAY to influenced by certain aspects of the industry.
    3-Requiring retrofitting for existing pools, some more than 50 years old, seems excesive and feels like it violates the spirit if not the letter of the constitutions ex post facto prohibition. For new pools I think the changes are a good thing, but there should have been a testing method provided so that existing pools could show that their old drain system was not a danger.
    4- Last but not least, the VGBA does not address private pools and spas, which is where the majority of the incidents (including the one the laws is named for) took place. So for backyard private pools it really only changes new construction.
    Local Health Department Public Pool Inspector.
    Review NEW public pool (4 or more living units) plans
    Inspect around 180pools or spas annually
    Most are in-ground Plaster, a few fiberglass, No above ground pools and only 1 or 2 spas.
    Charged with enforcing http://www.rules.utah.gov/publicat/c...2/r392-302.htm
    Use a Palintest Pooltest 9 Premier for most chemical tests

  10. #10
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    Re: How much chlorine is too much?

    Chem Geek I hope you are still watching this thread a bit. Do you have any data on where the FC will start bleaching swimming suits?
    Local Health Department Public Pool Inspector.
    Review NEW public pool (4 or more living units) plans
    Inspect around 180pools or spas annually
    Most are in-ground Plaster, a few fiberglass, No above ground pools and only 1 or 2 spas.
    Charged with enforcing http://www.rules.utah.gov/publicat/c...2/r392-302.htm
    Use a Palintest Pooltest 9 Premier for most chemical tests

  11. #11
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    Re: How much chlorine is too much?

    I don't have actual data on that, but anecdotal evidence supported by chemical theory. My wife swims in an indoor commercial pool over the winter 3-4 times a week that has had 1-2 ppm FC with no CYA in the water and every winter season her swimsuits get worn out where the elastic gets shot and the fabric gets thinner, basically having her need to get new swimsuits for each winter season. In our own outdoor pool with 3-6 ppm FC and 30-40 ppm CYA, her swimsuits have lasted for 9 summer swim seasons swimming almost every day though she now says she is starting to notice wear. The difference in active chlorine level between the two pools is roughly a factor of 10-20 which likely is reason for the difference. The same is true for the flakiness of her skin and frizziness of her hair between the two pools.

    Obviously the answer will depend on the actual fabric of the swimsuit and frequency of use, but I'd say that roughly speaking 40 expsoure-hours in 1-2 ppm FC with no CYA is probably when the swimsuit gets too worn out (assuming she was rotating between at least a couple of swimsuits). Remember also that there is physical deterioration from wearing the suit and swimming, not just from chlorine exposure, but the difference in experiences between the two pools shows that the chlorine difference is the major factor. In our own pool with an FC that is around 10% of the CYA level the swimsuits are lasting around 900 exposure-hours or so which is somewhat better than what the chemistry would predict.

    A shock level of chlorine where the FC is around 40% of the CYA level is equivalent to 0.6 ppm FC with no CYA so a swimsuit would last around 70-130 hours while at yellow/mustard algae shock level where the FC is around 60% of the CYA level and is equivalent to 1.5 ppm FC with no CYA so would last around 40 hours and be roughly similar to an indoor pool that didn't use CYA.

    Note that there is another factor that is dependent on the FC level alone and not on the active chlorine level. Namely, it is the chlorine capacity or reserve to continue to react with the swimsuit after one gets out of the water and such water evaporates. In this situation, a higher FC can lead to more swimsuit wear unless one rinses their swimsuit after they get out of the pool. My wife would normally do that with her suits except on weekends when we would both be using the pool and hang out in the sun after swimming.
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