Building insulation has been a construction concern for thousands of years; Persian engineers made insulated ice storage systems out of desert materials as early as 400 BC. As humans established themselves in cold climates year-round, it became vital to make sure that their dwellings could protect them from the winter temperatures. Over the centuries, many different materials have been used as insulation inside walls to help prevent heat from escaping the interior space. The housing industry became more commercialized during the Industrial Revolution, establishing a demand for better technology and building materials as mass production became the standard. It was during this time that American housing manufacturers hit on a new insulating material: asbestos. You probably know that asbestos is very dangerous, but what is it and how did it come to be inside so many walls?

The word ‘asbestos’ refers to six naturally occurring silicate minerals. They are made of long, thin fibrous crystals, which have good tensile strength and are resistant to fire, chemical, and heat damage as well as being excellent sound absorbers. The asbestos types are split into a number of different classes. The serpentine group, which has a layered structure of curly fibers, contains the chrysotile asbestos type; this common material accounts for about 95% of the asbestos found in American buildings and can be spun into fabric and formed into sheets. The amphibole class fibers are needle-like; they include amosite, crocidolite (also known as blue asbestos), tremolite, actinolite, and anthophyllite. All six of these asbestos types are known carcinogens and are now strictly regulated all over the world.

Asbestos is obtained through open-pit mining, where workers separate the mineral from the rocks and then process it into fibers or sheets. Believe it or not, asbestos has been used by humans for at least 4,500 years. Archaeological evidence in Finland shows that earthenware pots were made of clay mixed with anthophyllite; early written descriptions of an asbestos-like mineral date back to 300 BC, and the name ‘asbestos’ comes from the ancient Greek term meaning ‘inextinguishable’. Persian royalty would impress their guests with a dramatic display, cleaning asbestos cloths by exposing them to fire; the Holy Roman Emperor Charlemagne apparently had a whole tablecloth made of asbestos. The fire-resistant property of asbestos made it a fascinating, almost magical substance for many different people throughout history, and made it very attractive to builders.

When the Industrial Revolution transformed the building industry, engineers sought an easy, durable material for house insulation. The commercial asbestos industry began in earnest in the 1850s in the US, and became extremely widespread throughout North America. By the middle of the 20th century, asbestos was used in concrete, pipes, fireplace cement, ceiling insulation, flooring, roofing, drywall, and even lawn furniture. After World War II, Japanese manufacturers sprayed asbestos onto the structural frames in buildings and railroad cars, and even used it as an electrolyte in the production of ammonium sulphate, a common fertilizer for rice crops. But warning signs began to emerge as early as 1906, showing that asbestos had a dark, dangerous side. Next week we’ll examine how and why asbestos became one of the most infamous building materials ever used, and how the world reacted to discovering that their magic material was doing more harm than good.