Calcium Hypochlorite Safety

Operators commonly use calcium hypochlorite, also called HTH (high test hypochlorite), for cleaning clarifier weirs and disinfection purposes.

While HTH looks harmless and innocent, almost like laundry powder, it can be dangerous and deadly. HTH contains a chlorine concentration of 65 to 70 percent.

The CDC's National Institute for Occupational Safety & Health (NIOSH) has a Chemical Safety Card that summarizes the hazards and safety recommendations for using this chemical.

Also, be sure to review the Safety Data Sheet supplied with your delivery of HTH.

Here are some highlights on HTH safety: 

Personal Protective Equipment

Exposure to HTH can damage your skin, your eyes, and your respiratory system.

Don’t be fooled by the appearance of this chemical. Wear all protective equipment (breathing protection, eye protection, face shield, protective clothing and gloves). Prevent dispersion of the dust or powder, as it can be inhaled and result in harmful concentrations.


HTH reacts violently with many substances, including hydrocarbons (fuels, oils and greases), ammonia, and many metals. Store and transport this chemical in its original container, tightly closed. Be especially careful that any secondary containers used for applying HTH are clean and made of compatible materials.

Fire/Explosion Hazard

The National Association of State Fire Marshals, in their report, Assessing the Fire Performance of Calcium Hypochlorite and the Adequacy of Codes Governing its Storage in Retail Occupancies, describe HTH as “an extremely dangerous product that . . . can endanger both emergency responders and the general public with its potential for creating violent, intense fires and explosions.” It severely accelerates combustion and burns with extremely high temperatures.

HTH Lethal Fire 

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