Before it was recognized as a health hazard, asbestos was commonly used as insulation in residential and commercial construction because it is

Asbestos is a naturally occurring mineral fiber that was widely used in construction due to its desirable physical properties. Its primary and most valued characteristic was its exceptional resistance to heat and fire. This made it an ideal material for thermal insulation, fireproofing, and inclusion in products like roofing shingles, ceiling and floor tiles, and pipe insulation. Its use was prevalent before the severe health risks associated with inhaling its fibers, such as asbestosis and mesothelioma, were widely recognized and regulated.

B. water resistant. While some asbestos-containing materials offered water resistance, this was not the primary reason for its use as insulation; its fire-retardant quality was the key feature.

C. an air purifier. Asbestos is a hazardous air pollutant when its fibers become airborne and are inhaled. It does not purify the air; it contaminates it.

D. repellent to common pests. Asbestos was not used for its pest-repellent qualities. Its application was based on its physical properties of heat resistance, strength, and chemical inertness.

1. U.S. Environmental Protection Agency (EPA). "Learn About Asbestos." The EPA's official documentation states, "Asbestos is a mineral fiber... Asbestos fibers are resistant to heat, fire, and chemicals and do not conduct electricity. For these reasons, asbestos has been used in a wide range of products." This directly supports its use for fire resistance. (Accessed from the EPA's official website, epa.gov, under the Asbestos section).

2. Massachusetts Department of Environmental Protection (MassDEP). "Asbestos: Information for Homeowners." This state-level resource explains, "Asbestos is a mineral fiber that was added to a variety of products to strengthen them and to provide heat insulation and fire resistance." (Accessed from the Mass.gov website, specifically the page detailing asbestos information for property owners).

3. National Cancer Institute (NCI) at the National Institutes of Health (NIH). "Asbestos Exposure and Cancer Risk." Fact Sheet, Section: "What is asbestos?". The document states, "It is also resistant to heat and fire... Because of these properties, asbestos has been used in a wide range of manufactured goods, including... insulation." (Accessed from cancer.gov, Publication Date: May 15, 2019).