Overlooked Inherent Hazards of Commonly Used Pool and Water Treatment Chemicals

Common pool chemicals are not classified as water reactive chemicals and are not considered by the general public to be hazardous. Why should they be? They are widely used to treat and disinfect pools and spas all over the world. When used to disinfect large quantities of water (dissolved in large amounts of water) and/or when stored or transported dry and without confinement, their reactivity hazards are negligible.

This paper will show that when common pool chemicals are confined and heated they decompose violently and generate large quantities of gaseous products. Decomposition may also initiate without added heat for some formulations under certain conditions. Adiabatic calorimetry measurements show that decomposition rates are exceedingly fast and rival the decomposition of propellants and some explosives. The decomposition products can be both flammable and/or toxic.

When partially wet and confined, for example during processing, storage, or transportation, the same water reaction that is intended to disinfect large amounts of water can trigger the decomposition of these materials, potentially leading to severe fires and explosions.

Confinement can be exhibited when wet pool chemicals (small granules and/or powder) are stored in a sealed container or when stored in bulk in large quantities. A three to four feet of powder over a crusted wet cake of pool chemicals can form a sufficient sealant to permit the formation of highly unstable nitrogen trichloride (NCl₃) or nitrogen tribromide (NBr₃). If the concentration of NCl₃ or NBr₃ gets high enough, the spontaneous decomposition of these unstable chemicals acts as a trigger for the decomposition of the pool chemical itself, which can lead to severe fires and explosions. It is important to note that pool chemicals powders are also poor conductors of heat.

This paper provides irrefutable evidence and learnings from more than forty measured calorimetry and analytical tests data sets as well as thermochemical evaluations that demonstrate the mechanism of how partially wet and confined pool chemicals can cause severe fires and explosions. Recent incidents involving common pool chemicals during processing and storage are also shared.