While a gasket is used to fill the space between two parts of a machine, the combination of a gasket and a heat seal also insulates that space so that heat does not transfer between mechanical parts. The heat seal needs to be made of something that is not only a poor conductor of heat but is also easy to compress in order for the gasket to work properly.
Many types of heat seals were largely made with asbestos during much of the 20th century. Asbestos was known for its insulating properties. It was also highly compressible, easy to acquire, and was cheap. Prior to 1980 just about every home and other building contained an asbestos heat seal or gasket. Since it was used so frequently, many of those people who manufactured the heat seals or put together machines that had asbestos gaskets were exposed to asbestos. Anyone who owns, works with, or uses any type of machine with an asbestos heat seal may be exposed to asbestos.
Asbestos exposure accounts for about 10,000 deaths a year in this country. Inhaling or ingesting asbestos can cause one of a number of serious illnesses that include lung cancer, asbestosis, and mesothelioma. There is no cure for mesothelioma, and it often goes undiagnosed until it is in its later stages.