Liquid bleach -- a solution of water and sodium hypochlorite -- is used in the home to clean and disinfect clothes, floors, tabletops and bathrooms. Still, just because bleach is a household product doesn't mean it is not dangerous. In fact, bleach is especially dangerous when heated and is not suitable for use on or near heated areas such as the oven.
Bleach is regularly heated in your clothes washer to no effect. This is because the amount of bleach being used is small and well diluted in gallons of water. Additionally, while the heat produced in a clothes washer is significant enough to activate the detergent, it is not enough to separate the chlorine in the bleach from its water base. No danger of injury exists when using bleach in the clothes washer, but the danger to color in clothing is very great. Use only color-safe bleaches on clothes.
Unlike the bleach used in a clothes washer, bleach boiled in a pot or placed next to a portable space heater is downright deadly. At boiling point, the water in the bleach mixture becomes vapor and releases chlorine gas. This yellow-green gas can cause severe chemical burning to the lungs and even suffocate those who can't get away from it in time. It was used as a weapon in World War I to choke enemy soldiers out of their trenches.
Another way to release dangerous chlorine gas is to heat the bleach chemically. Unfortunately, this is all too easily accomplished by mixing bleach with another common household cleaner, ammonia. When the two combine, the chlorine in the bleach heats up until the chlorine gas overflows. When combined in a small vessel such as a soda bottle or a flask, this chemical reaction explodes violently.
Like its liquid cousin, powder bleach, or calcium hypochlorite, is sensitive to heat from chemicals and from conventional heating methods such as an open flame or a boiling pot. Heating powder bleach on metal such as the bottom of a copper pot can have a corrosive effect, and mixing the powder in a solution with ammonia will produce the same effect as with liquid bleach.