Never mix Phosphoric acid with Sodium hypochlorite (chlorine bleach)
Toxic gas
The regulator's instruction is that phosphoric acid must be stored to avoid contact with water, ammonia, BLEACH and nitromethane because violent reactions occur. Acid and hypochlorite together release chlorine gas, which is a severe respiratory irritant. In a bathroom the space is small and the concentration builds quickly. Leave the room, do not return to open a window, and seek medical advice.
Precautions
- Never mix with other cleaning products
- Ventilate the area
- Wear gloves
- Wear eye protection
- Keep away from children and pets
- Rinse thoroughly afterwards
- Consider professional help
How this happens
Hypochlorite is stable in alkaline solution and unstable in acid: lowering the pH drives it to release chlorine. That is the same chemistry as the vinegar-and-bleach accident, arriving through a different product. This version matters because phosphoric acid is what a large share of commercial limescale removers and rust treatments are built on, so the reader performing the reaction is not combining a food ingredient with a cleaner — they are using two cleaning products from the same aisle, one after the other, on the same surface.
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
- Phosphoric acid — A moderately strong acid used in descalers and rust treatments. The regulator's storage instruction names bleach among the things it must never meet.
- 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: Phosphoric Acid (RTK 1516)
New Jersey Department of Health, 2004 · Government or regulator
Relied on for: That phosphoric acid must be stored to avoid contact with water, ammonia, bleach and nitromethane since violent reactions occur. (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 releases chlorine gas on contact with acid and that medical observation is recommended after overexposure. (states this directly)
Hazard Alert — Worker Health and Safety: Mixing Bleach with Other Cleaning Products Can Be Deadly
New Jersey Department of Health, Environmental and Occupational Health Surveillance Program · Government or regulator
Relied on for: That acidic products must not be combined with bleach because chlorine gas is produced. (states this directly)