<P> During the 1980s and again in the 1990s it was suggested at times that the process of making asbestos cement could "neutralize" the asbestos, either via chemical processes or by causing cement to attach to the fibers and changing their physical size; subsequent studies showed that this was untrue, and that decades - old asbestos cement, when broken, releases asbestos fibers identical to those found in nature, with no detectable alteration . </P> <P> Exposure to asbestos in the form of fibers is always considered dangerous . Working with, or exposure to, material that is friable, or materials or works that could cause release of loose asbestos fibers, is considered high risk . In general, people who become ill from inhaling asbestos have been regularly exposed in a job where they worked directly with the material . </P> <P> The most common diseases associated with chronic exposure to asbestos are asbestosis and mesothelioma . </P> <P> Fiberglass insulation was invented in 1938 and is now the most commonly used type of insulation material . The safety of this material has also been called into question due to similarities in material structure . However, the International Agency for Research on Cancer removed fiberglass from its list of possible human carcinogens in 2001 and a scientific review article from 2011 claimed epidemiology data was inconsistent and concluded that the IARC's decision to downgrade the carcinogenic potential of fiberglass was valid (however, this study was funded by sponsored research contract from the North American Insulation Manufacturer's Association). </P>

When was asbestos first used in the united states