The World Health Organization (WHO) Free Available Chlorine (FAC) limit for swimming pools as described in
this link is as follows:
It is recommended that acceptable levels of free chlorine continue to be set at the local level, but in public and semi-public pools these should not exceed 3 mg/l and in public and semi-public hot tubs should not exceed 5 mg/l. It is recommended that total bromine does not exceed 4 mg/l in public and semi-public pools and 5 mg/l in hot tubs.
The EPA limit is based on drinking water standards and is 4 ppm as shown in
this link.
This discussion from NCCEH in Canada describes maximum Free Available Chlorine (FAC) of 5 ppm or 10 ppm depending on the province/territory or other source.
The states of Florida and Wisconsin allow FC up to 10 ppm in their state codes. Florida's code specifically states the following:
2. Disinfection – Free chlorine residual shall be 1 milligram per liter (mg/L) to 10 mg/L, inclusive, in conventional swimming pools and 2 mg/L to 10 mg/L, inclusive, in all other type pools such as spa-type pools and interactive water fountains; bromine residual shall be 1.5 mg/L to 10 mg/L, inclusive, in conventional swimming pools and 3 mg/L to 10 mg/L, inclusive, in all other type pools. Except that, the following maximum disinfectant levels shall apply to indoor conventional swimming pools: 5 mg/L free chlorine or 6 mg/L bromine.
The reason for the lower limit indoors is that typically CYA is not used indoors (even though it probably should at low levels such as 20 ppm).
The reason for such variations is that none of these agencies have an understanding of the chlorine/CYA relationship. CYA significantly moderates chlorine's strength. In pool water at cooler temperatures, 10 ppm FC with 50 ppm CYA at pH 7.5 has the same active chlorine (hypochlorous acid) level as 0.09 ppm FC with no CYA while at hot spa temperatures of 104ºF, it's equivalent to 0.51 ppm FC with no CYA.
This is the main reason why commercial/public pools and spas with > 1 ppm FC and no CYA (typically indoors or spas, but sometimes outdoor pools) are much harsher on swimsuits, skin, and hair. So if you have CYA in the water, say from using Dichlor, then you shouldn't worry about higher FC levels being unsafe. The FC would only come into play if you were to drink the water in large quantities. Drinking water standards limit FAC to 4 ppm assuming drinking 2 liters of water every day for a lifetime.
