Sciencemadness Discussion Board

Incompatibility of caclium hypochlorite and sodium dichloroisocyanurate

woelen - 7-9-2008 at 12:11

Last week, a nasty accident happened to someone in Breda, a city in the Netherlands.

A guy has a swimming pool and wanted to clean this. He used so-called "shock"-granulate for this. Over here, there are two products, called "shock 63" and "shock 70". Both are sold in the same jar, a blue jar with waves of water on it, one jar is labeled "Shock 70" and the other is labeled "Shock 63". Besides this, they are the same. The shock 63 is almost 100% pure sodium dichloroisocyanurate (Na-DCCA), the shock 70 is 85% or so of calciumhypochlorite (active chlorine is 70%).

The guy in Breda first put some shock 70 in his pool, and when this bottle was empty, he tok his new bottle of shock, which happened to be shock 63. He added a little water to make a slurry of it, intending to brush the swimming pool. After a minute or so, the heap of slurry started bubbling, big bubbles of gas, at the size of a football were produced. The slurry was partially charred.

This man could escape, but has severe lung damage and probably will not completely recover from this accident. His two dogs both died in the chlorine gas.

I did the same experiment. I mixed 500 mg of each chemical and added some water, such that it becomes a slurry. Quite some heat is produced, a lot of Cl2, and in my situation a big yellow drop of oil was produced (most likely NCl3).

I did not know this very dangerous thing. The two shock products, which are very similar and are used for the same purpose react with each other in a violent and dangerous reaction, giving really nasty products. A layman can be killed by this.

Does anyone of you know what is the precise reaction, which occurs over here? I really am surprised to see that two such chlorine-based products reacts in such a drastic way with each other.

Right now, in the Netherlands, all chlorine-based pool products need to be relabeled, with extra warnings.

Formatik - 7-9-2008 at 13:14

Quote:
Originally posted by woelen I did the same experiment. I mixed 500 mg of each chemical and added some water, such that it becomes a slurry. Quite some heat is produced, a lot of Cl2, and in my situation a big yellow drop of oil was produced (most likely NCl3).


That's right. And to further prove it is NCl3 a fraction of that drop will detonate on contact with olive oil or turpentine. From the sound of it, it sounds like pretty large amounts. Lucky to not have encountered an explosion.
Quote:
Bretherick’s Handbook of Reactive Chemical Hazards

Although calcium hypochlorite is used in conjunction with sodium dichloroisocyanurate (usually as the dihydrate) for swimming pool maintenance, they must not be mixed undiluted. Noxious fumes and violent explosion or fire can result [1]. Although the organic compound is, at first sight, at its highest oxidation level, it contains disguised ammonia, and nitrogen trichloride may appear on reaction with hypochlorites [2].

1. Jones, C., INTERNET: CatJones@FC. KERN.ORG
2. Kirk Othmer, 1998, Vol. 25, 592