Treatment Plant Safety
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Calcium Hypochlorite

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.

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 (eye protection, face shield, protective clothing and gloves. Be especially careful about dispersing the 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.

The Center for Disease Control website has a Chemical Safety Card that summarizes the hazards and safety recommendations well.

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.

Material Safety Data Sheet

Be sure to review the MSDS for calcium hypochlorite before using it. Just because it’s commonly used by the public (for swimming pools) doesn’t make it harmless. On the contrary, this chemical needs to be transported, stored and used with special care.

More Information

HTH accident

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