Here and here are some good articles about it. The only thing is, it's a pretty serious chemical. It's an oxidizer and when a large amount of it mixes with a small amount of water, it can be highly reactive, generating high temperatures. HTH is self-reactive anyway, and produces chlorine gas as it decomposes. The fumes can be deadly if a person breathes too much of it. As an oxidizer, it's also corrosive, so calcium hypochlorite - and its vapors - need to be kept from contact with anything metal. It's probably not a good idea to store it around electronics either. Lastly, keep it away from other chemicals. If a spill were to occur and calcium hypochlorite accidentally mixed with another chemical, a fire could result.
We had several bags of HTH, and the hubster decided to give one to The Neighbor. The photo above is not the actual stuff we bought, but what we did buy was packaged in the same style - a sort of plastic, one-pound bag. (I've since learned that calcium hypochlorite is packaged in breathable containers to avoid pressure buildup while in storage). When we originally bought the calcium hypochlorite, the hubster put the bags inside a bucket, labeled the bucket with all kinds of warnings, and then placed the bucket inside a large, rubberized trash can we use for newspaper recycling. The idea was that the newspaper would soak up any humidity (or other moisture), hopefully keeping the HTH safe.
When the hubster opened the bucket to pull a bag out for The Neighbor, he found a surprise. Firstly, the fumes had built up in the bucket more than he anticipated, and he had to quickly step away to avoid breathing the chlorine gas. Once the fumes dissipated, he found that inside the bucket, the bags had grown brittle, and all but disintegrated in his hand when he tried to pick them up. He had also stored some instructions for use along with the store receipt inside a ziploc bag inside the bucket. The papers had turned a dull grey, making it unreadable, and came apart at the folds when I tried to take them out of the bag.
So, what have we learned here?
- HTH is no joke. It's a very strong, very deadly chemical.
- Don't leave HTH in the cheap plastic bag it's sold in. It doesn't take long for the bag to become brittle and fall apart.
- While it needs to be stored in such a way that there's little, if any, chance that it could come into contact with moisture or with metal, one still has to be aware of chlorine gas buildup when opening the storage container. It's best to open the container outdoors or in a very-well-ventilated area. Be prepared to step away in order to avoid breathing deadly fumes.
- The bucket we have our calcium hypochlorite stored in, is probably not a full-proof, long-term storage solution. Eventually the bucket will probably become brittle and crack. We will continue researching better storage methods. I read at least one suggestion online to keep HTH in glass reagent bottles with a ground glass stopper. In the meantime, our plan is to check on the bucket about every three months or so to ensure its integrity.