some larger public pools actually use a gas based chlorination system.A few years ago, several people required medical attention after going to a local swimming pool. Apparently, there was a problem with the chemicals used to clean the waters (can't remember if it was a matter of proportions, wrong labels or both), but people had to be taken to the hospital to recover.
The incident gained some notoriety because of the weird explanation given to the news by the young pool watcher (perhaps a teenager) that did the mixture, not by the fact that she probably was a minimum-wage worker without any knowledge or experience to do such things.
also, large public pools that still use solid or liquid chlorination are required to have oxygen tank nearby because of the large volumes of the chemical.