Chapter 4: Bleaches and brighteners · Part 2: Chlorine bleaches (and ammonia)
Calcium hypochlorite
- Poison schedule (Australia)
- Contaminant risk
The worst fact: of every product behind more than 100 calls to the NSW Poisons Information Centre in 2014–15, pool chlorine (all types) had the highest share of callers with symptoms: 68%. It reacts explosively with TCCA pool tablets and water, and the US EPA warns that even a small splash of water on pool chemicals can in some cases trigger a strong reaction.
Why brands use it: it's a strong, dry, cheap source of chlorine for pools and drinking water.
Take care if: you have children or a pool shed. In the US, an estimated 4,876 people went to emergency with pool chemical injuries in 2012, almost half of them under 18. Keep it dry, locked away, and separate from other pool chemicals. In Australia, granular pool chlorine (about 65% available chlorine) is a Schedule 6 Poison.
Comes from: chlorine reacted with lime (calcium hydroxide) and caustic soda.
Myth check: "A strong pool smell means lots of chlorine": not really. The US Centers for Disease Control and Prevention says that smell comes from chloramines, made when chlorine reacts with sweat and urine.
Contaminants: bromate and chlorate. In a Spanish study of water-treatment calcium hypochlorite, 10 of 14 pellet samples contained bromate (median 240 mg/kg), and the median chlorate level was 9,516 mg/kg. They're unlikely to matter at normal pool doses, but it's a factor you can't see on the label.
Fair to say: for almost 100 years, pool chemicals like this have been the main thing stopping germs spreading in pools.
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
- ACCC. Analysis of consumer product related calls to the NSW Poisons Information Centre, June 2014 to May 2015 (2016). productsafety.gov.au
- US EPA. A Brief Guide to Mold, Moisture, and Your Home (EPA 402-K-02-003); Safer Choice Safer Chemical Ingredients List; Chemical Safety Alert: safe storage and handling of swimming pool chemicals (2001).
- MMWR. Chang et al. 2020;69(16); Gharpure et al. 2020;69(23); Hlavsa et al. 2014;63(19).
- Garcia-Villanova RJ et al. Bromate and chlorate in hypochlorite used for water treatment. Sci Total Environ 2010.
The full source list is at the end of Chapter 4.