The solid form for the distribution of chlorine is calcium hypochlorite. It is 65% chlorine. Since the chlorine is "riding along" with the calcium, it degrades over time and under various conditions releases chlorine gas. The granules are both explosive and combustible, and react with chemicals, moisture, impact and heat, releasing the chlorine as gas. The container may present disposal issues, and a partially filled container will contain chlorine gas.

Granules begin losing strength after the container has been opened.
The liquid form for distribution of chlorine is sodium hypochlorite, also called "bleach" which is 12.5% chlorine and 7/8 water. It comes in tanks and drums and degrades over time and in various conditions, can release chlorine gas. It is both flammable and explosive when combined with other oxidants or contaminants. Sodium hypochlorite is reactive with chemicals, heat, organics and releases chlorine gas. The container may present disposal issues, and a partially filled container will contain chlorine gas.

Bleach can lose up to 50% of its potency within 90 days. It can actually get as low as 3% strength.
Gas chlorine is 100% chlorine, and does not degrade over time. It is non-flammable and non-explosive, although it will react with an oxidizer. There are no container disposal issues since the tank is reused.

One pound of gas provides about the same disinfection level as 1.5 pounds of granules and 1.2 pounds of bleach, yet costs less.

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Granules

Bleach

Gas