Swimming Pool Chemical Explosion

A homeowner was treating her swimming pool with a chlorinated chemical oxidizer used to control bacteria and algae (analogous to chlorine bleach.)  The instructions for the chemical said to add the chemical directly to the pool and not add water to the chemical.  Instead, the homeowner added water to the bucket of chemical and planned to pour the contents into the pool.  As she carried the bucket across the yard to the pool, the chemical began to release a choking, greenish gas.  She attempted to close the lid on the bucket, but this resulted in the bucket rupturing and spraying water and chemical in her face.

ESi determined that when the chemical was mixed with a small amount of water, an undesirable side reaction occurred that produced chlorine gas and possibly trichloramine (a shock sensitive chemical that can detonate.)  Mixing the chemical with large amounts of water prevented this reaction from occurring.