Never mix Sodium dichloroisocyanurate with Sodium hypochlorite (chlorine bleach)
Toxic gas
The regulator's own wording is that the two react EXPLOSIVELY in the presence of water — which is to say, in the only circumstances either product is ever used in. Both are chlorine sources, so chlorine gas is released as well, and chlorine is a severe respiratory irritant whose effects can be delayed. If this has happened, get into fresh air at once, do not go back into the room to ventilate it, and seek medical advice. Feeling better shortly afterwards is not an all-clear.
Precautions
- Never mix with other cleaning products
- Ventilate the area
- Keep away from children and pets
- Rinse thoroughly afterwards
- Consider professional help
How this happens
Sodium dichloroisocyanurate is a solid chlorine donor: it holds chlorine in a stable form until water releases it, which is what makes a tablet convenient. Sodium hypochlorite is already a chlorine solution. Bringing a concentrated donor into contact with a hypochlorite solution is an uncontrolled release rather than a dilution, and the state health department describes the outcome as explosive. The realistic route to it is not deliberate mixing but sequence — a tablet dropped into a sink or a bucket that still holds bleach solution from the previous job.
If it has already happened
Get everyone into fresh air straight away, and do not go back inside to open windows. Anyone with breathing difficulty, chest pain, persistent coughing, or a chemical splash to the eyes needs medical attention — treat it as an emergency and call your local emergency number. In the United Kingdom, use NHS 111 or 999 as appropriate; clinicians can consult the National Poisons Information Service.
The substances involved
- Sodium dichloroisocyanurate — The chlorine donor in sanitising and sterilising tablets. A state health department records it as reacting explosively with bleach in the presence of water.
- Sodium hypochlorite (chlorine bleach) — A powerful oxidising bleach and disinfectant. It is also the substance behind the most common serious household chemical accidents, and must never be mixed with anything.
Evidence
Strongly supported
Sources
Right to Know Hazardous Substance Fact Sheet: Sodium Dichloro-Isocyanate (RTK 1694)
New Jersey Department of Health, 2002 · Government or regulator
Relied on for: That sodium dichloroisocyanurate reacts explosively with calcium hypochlorite or sodium hypochlorite in the presence of water, and that it reacts with water to produce chlorine gas and nitrogen trichloride. (states this directly)
Right to Know Hazardous Substance Fact Sheet: Sodium Hypochlorite
New Jersey Department of Health · Government or regulator
Relied on for: That sodium hypochlorite is a corrosive oxidising agent and that medical observation is recommended for 24 to 48 hours after overexposure because pulmonary edema may be delayed. (states this directly)
Right to Know Hazardous Substance Fact Sheet: Chlorine
New Jersey Department of Health · Government or regulator
Relied on for: That chlorine is a severe respiratory irritant with established occupational exposure limits. (background and mechanism only)