There are no absolute ranges, and the data and analysis has continued to develop since I first published the 'Best Guess" chart nearly 14 years ago. Currently, we're not completely sure what happens at very high levels of chlorine, even when the CYA is also very high. It doesn't seem to be a problem for people -- over the past week a local 200,000 country club pool I service has been at CYA=~100 ppm and FC=~25 ppm, with no complaints or problems.

But we're still not sure that a level like CYA=100 and FC=40 won't bleach suits or liners, though we're pretty sure it won't be a problem for 90+% of swimmers. We do KNOW that it's not dangerous, because bleach baths (CYA=0, FC=50 - 100 ppm) have been used by dermatologists for years to treat both adult and pediatric patients.