There are some grout cleaners that cause toxic fumes, especially those with high concentrations of bleach or certain acids. Muriatic, or hydrochloric acid, is one of the most dangerous acids used as a grout cleaner. When mixed with water, it produces highly corrosive vapors that can etch chrome and bathroom fixtures as well as destroy lung and skin tissue. The fumes are also flammable and undetectable, and they can easily travel throughout the house.
Small pockets of acid crystals may become trapped in porous surfaces of grout and tile after rinsing and then emit fumes when they come in contact with water or other cleaners. Grout cleaners with strong concentrations of chlorine bleach also emit toxic fumes when exposed to carbon dioxide or other chemicals. The vapor formed by chlorine bleach is a severe lung irritant that is fatal in high concentrations.
Although most commercially available products for household grout cleaning are generally safe when used as directed, they can become lethal when consumers disregard safety precautions. Mixing chlorine bleach with ammonia or acids produces gases that are undetectable and often fatal, especially when used in poorly ventilated areas where grout tends to need the most cleaning.
Experts recommend using products that contain nontoxic chemicals such as oxygen bleach, which produces no fumes. Household mixtures of baking soda with vinegar or lemon juice are also effective for cleaning tile and grout without producing toxic fumes.