Fire doors have been used commercially, as well as in homes, as a passive fire-fighting measure to prevent the fire from spreading into other areas of the structure. Often they are designed to shut automatically once a fire has been detected. Once the doors close, the fire should be contained behind them, giving firefighters time to control a blaze and minimize the resulting damage.
A fire door is made up of several different components, including steel, glass, and gypsum, but many older doors contain vermiculite boards. Vermiculite is an ore compound, and thus must be mined from the ground. However, vermiculite and asbestos are similarly-structured materials, and are often found in the same veins. Sometimes the vermiculite can become contaminated with asbestos during the mining process, and that asbestos can end up in the interior of a fire door.
As long as the door is not damaged, the asbestos will remain inert and non-harmful. However, if the door should break or the vermiculite board otherwise become damaged, the asbestos it contains can be released into the air. Breathing in these asbestos particles is extremely dangerous.
Recently, steps have been taken to eliminate the danger of asbestos from fire doors. Not only has the vermiculite mining process been regulated to prevent asbestos contamination, but the vermiculite boards have largely been replaced with gypsum as a flame-retardant filling for the doors.
Despite these measures, for some, it is too late. The effects of asbestos exposure might not surface until decades later, resulting in such conditions as asbestosis, lung scarring, or malignant mesothelioma, an aggressive form of lung cancer.