Calcium Hypochlorite

Calcium hypochlorite tablets are placed in canisters and pool water is bypassed through the erosion feeders, dissolving the tablets and introducing chlorinated water back into the pool. Clogging with the feeders was an issue in the past, but most of those issues have now been resolved through design.

Calcium hypochlorite is easier to handle than liquid chlorine.  It has a pH of 12, so it doesn’t require as much buffering agent as liquid chlorine.  It’s more expensive than liquid chlorine (approximately $1.80 per lb.), but it has a much higher concentration of available chlorine (65%).  First-dollar costs are similar, and even thought the tablets are more expensive than liquid, the need for fewer buffering agents and a longer shelf life provide trade-offs that make the operational costs manageable.  There is no need for the barrier systems and huge storage tanks required for liquid chlorine.

Calcium hypochlorite is typically delivered in 5-gallon plastic containers that weigh approximately 50 lbs.  The containers are not fire rated.  Calcium hypochlorite is relatively safe to handle and store.  The container must be sealed at all times as the tablets cannot come into contact with other chemicals.  The combination of a high concentration of chlorine combined with calcium makes it very reactive.  When it comes in contact with other chemicals, the reaction will release chlorine gas into the air and could possibly explode.  When on fire, it will produce its own oxygen.

Calcium hypochlorite is a Class 3 oxidizer and is corrosive.  As such, it is considered a High Hazard level 2 content by NFPA 1.  Some codes limit storage from 10 to 200 lbs. in a single location. NFPA 1 limits quantities of solid class 3 oxidizers to 10# in a control area except where the contents are necessary for maintenance, operation, or sanitation of equipment.  Cal hypo is considered necessary for the operation of a pool sanitation system. Therefore, a maximum quantity of 220# can be stored in a control area without triggering a requirement for H-2 occupancy. Typically, the 10# max allowable quantity can be increased by 100% if the space is provided with an appropriate sprinkler system and the material is stored in an approved container.  Additional storage of calcium hypochlorite can be provided in an additional “haz-mat” room (referred to as a control area) if the building has such a room. Control areas for cal hypo that do not exceed quantities listed shall have a 1-hour rated fire barrier separating the room from the rest of the building.

The H-2 occupancy requirement is based on a closed system that operates over 15 psi. While most specified cal hypo systems operate below 15 psi, there are instances where the systems will exceed 15 psi. H-2 is a worst case scenario.

Where the quantity of cal hypo stored in a single location exceeds the 220# MAQ listed, the room must meet the requirements for Protection Level 2, as listed in NFPA 1 and NFPA 400. This includes a 4 hour fire rating adjacent to assembly occupancies, a maximum 100ft travel distance for egress, 25% minimum of the room perimeter shall be on the exterior of the building, and other requirements.

Although secondary containment is not required by code unless a single cal hypo vessel contains over 550#, it is recommended to provide secondary containment for the Owner’s peace of mind.

CH prefers is to use cal hypo on all indoor facilities, although, with UV, liquid chlorine is acceptable for indoor pools.  In the case there are indoor and outdoor pools at the same facility, it is CH preference to specify the same system for consistency.

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