What Is Calcium Hypochlorite?

The New Jersey Department of Health describes calcium hypochlorite as a white powder, granule or pellet with a strong chlorine-like odor that is used to kill algae and bacteria, in bleach and in pool chemical products. It says contact can severely irritate and burn the eyes and skin, that breathing it can irritate the nose, throat and lungs, causing coughing or shortness of breath, and that higher exposures may cause a build-up of fluid in the lungs, a medical emergency.

Storage and mixing matter. The New Jersey Department of Health says calcium hypochlorite is not flammable but is an oxidizer that may ignite combustibles such as wood, paper and oil, and that it must be stored to avoid contact with strong acids, ammonium compounds, amines, metals, strong bases, organic fuels, halocarbons and sulfur because violent reactions occur. An EPA chemical safety alert says the most common pool chemicals are inherently incompatible with each other, that mixing them can generate temperatures high enough to ignite nearby combustible materials and release highly toxic and corrosive chlorine gas, and that pool chemicals are meant to be added to large quantities of water, since adding a limited amount of water to a chemical can cause an unwanted reaction that raises the temperature and releases toxic gas.

A 2019 CDC Morbidity and Mortality Weekly Report estimated that pool chemical injuries led to 13,508 US emergency department visits during 2015 to 2017, and said about 90% of patients diagnosed with poisoning were injured by inhalation rather than ingestion.