Chapter 4: Bleaches and brighteners · Part 2: Chlorine bleaches (and ammonia)
Trichloroisocyanuric acid (TCCA)
- Poison schedule (Australia)
The worst fact: a small amount of water that doesn't dissolve it can make it heat up and give off chlorine gas and explosive nitrogen trichloride. After a hurricane wet a US store of over a million pounds of it in 2020, a highway was closed for over 28 hours and nearby residents were told to stay inside.
Why brands use it: it dissolves slowly, so one tablet keeps releasing chlorine for days. It's about 90% available chlorine.
Take care if: you store it. Keep it dry, away from other pool chemicals, and away from anything containing ammonia. In Australia it's a Schedule 6 Poison (it's about 90% available chlorine).
Comes from: urea, heated to make cyanuric acid, then reacted with chlorine and caustic soda.
Myth check: nil.
Contaminants: nil.
Fair to say: dissolved and diluted as directed, it didn't irritate skin in a week-long human test.
Correct as of November 2026. What the badges mean
Sources
- Australian Government. Poisons Standard October 2026 (SUSMP), F2026L01327: chlorinating compounds, dichloroisocyanuric acid, hydrogen peroxide, sodium percarbonate, peracetic acid, ammonia.
- Safe Work Australia. Hazardous Chemical Information System (HCIS): classifications for each chemical, and for borax. hcis.safeworkaustralia.gov.au
- US Chemical Safety Board. Bio-Lab Lake Charles TCCA reaction, decomposition and toxic gas release: final report (2023).
The full source list is at the end of Chapter 4.