What is Asbestos?

Webster’s Dictionary (1984 Edition) defines asbestos as “a fire-resistant, fibrous mineral used in fireproofing, electrical insulation, etc.”

Before asbestos became associated with disease in the public’s mind, most people thought of asbestos as something fireproof. This manifested itself in the popular culture from time to time. Mad magazine, for example, once featured the omnipresent Alfred E. Newman in the character of the Roman emperor Nero, with the epitaph: “sold asbestos togas while Rome burned.” This was in the late 1950s. A popular item for outdoor chefs in suburbia was a pair of asbestos barbecue mittens, and many homes had ironing boards with asbestos covers. In fact, that suburban home may also have had shingles and siding that were reinforced with asbestos, floor tiles with asbestos, a heating system and boiler insulated with asbestos, asbestos-containing acoustical plaster, wallboard and joint compound in the walls, and so forth. The cars in the garage would have had asbestos coated brake linings, and, if they had stick shifts, asbestos coated clutch surfaces. The water from the municipal water supply might have come through concrete pipes reinforced with asbestos. That is just some of the “etc.” from the dictionary definition quoted at the left. Most people did not (and still don’t) think of asbestos in these ways — if they thought about it at all they thought of the barbecue mittens.

To put it as plainly as possible, asbestos is a rock. That is where its “fireproof” quality comes from (just try to build a fire with rocks and see what happens). Like most rocks, its molecular structure is that of a crystal, like quartz and many other minerals. These crystalline minerals have a curious property — they fracture along the lines of the shape of the crystal. Quartz, for example, has a crystalline structure that is a cube. If you have big cube of quartz, and you bang it the right way with a hammer, it will fracture into four identical little cubes. Mica, another mineral, fractures into sheets which can actually be pried off with the blade of a knife. The molecular (crystalline) structure of asbestos is that of a fiber. If you pound asbestos fibers hard enough, they break down into narrower, thinner fibers. The fibers are also flexible. There is one other critical characteristic of asbestos — a result of it being a rock that is found in natural deposits in the ground — it is free. Of course, you have to dig it up and process it and all that, but its cost is very low, especially when compared to synthetic substitutes like fiberglass or rockwool (which are made by heating the glass or rock to a very high point so it turns into a thin liquid, and then blowing air through it — this is the way cotton candy is made, too; just look inside the cotton candy machine the next time you go the movies).

There are three types of asbestos fiber that have had commercial uses in this country: chrysotile, amosite and crocidolite. Chrysotile fibers are fundamentally different from the other two. Chrysotile fibers are called serpentine, because of certain characteristics they have. Amosite and crocidolite (and other mineral fibers, such as tremolite) are called amphiboles. Amphibole fibers are long, straight and rigid. Most of the amphibole fiber (the vast majority of it was amosite) used in the United States came from South Africa (some crocidolite also came from Australia). Mines in Quebec, Canada, supplied the chrysotile fiber used in the United States, except for a single mine in Vermont.

There is a body of medical opinion to the effect that amphibole fibers are more likely than chrysotile to cause mesothelioma. This is the foundation of what is known as the “fiber defense” in mesothelioma cases, used by certain companies whose products only contained chrysotile fiber. There is another body of medical opinion to the effect that all fiber types are carcinogenic and that all are implicated in mesothelioma.

The main usefulness of asbestos to industry is that it consists of essentially indestructible fibers. It is not, in fact, a particularly good insulator. What it does is give tensile strength to substances that are. This can be illustrated by looking at the use of steel-reinforced concrete in construction. Concrete has poor tensile strength. If you make a long, thin object out of concrete, it will break very easily. Concrete has what is called compression strength — a cube of solid concrete can support tremendous weight without breaking or flexing. Steel, on the other hand, has great tensile strength. That is why we make tools out of it. Its compression strength, however, is not that great, because it can flex, and will soften and melt when heated (that is why we can work with it). This is why, when you see a large building going up, the foundation will be made of concrete, and the frame will be made of steel.

Many applications, like bridges, pipelines and certain types of buildings (e.g., parking garages) or foundations on soft, swampy ground, require the use of something that has both tensile and compression strength. The substance that is used is steel-reinforced concrete. A structure of steel reinforcing rods (called “rebar”) is assembled, and the concrete is poured over it. When the concrete sets up, the resulting structure will be made of what looks like concrete, but it will be strong because it has steel rods inside it, supporting its structure and giving it tensile strength.

This is the same function performed by asbestos fibers in many of the products into which they were incorporated. Much pipe and boiler insulation, for example, was made out of magnesia at one time. Magnesia is an excellent insulator, but it is very brittle and crumbles easily, so you cannot make pre-molded pipe insulation out of pure magnesia. If, however, you mix asbestos fibers into the liquid magnesia, and then mold it, you will have a product that holds together and won’t break up so easily. This characteristic, in industrial parlance, is called handleability. The product was known as “85% Magnesia” or, in the field, “85 mag.” When calcium silicate gradually replaced magnesia as the preferred high temperature insulation in the 1950s, asbestos was again used to reinforce the product, in the same way, and for the same reason. Asbestos also has the advantage of not being affected by the high temperatures generated by some of the manufacturing processes involved (for more on this, see the Owens-Corning article).

Asbestos was also used as a reinforcing fiber in wallboard, siding, roofing shingles, gaskets, floor tiles and countless other products. It was used for its heat resistance in brake linings and other friction products, as well as in high-temperature applications like boiler cements. The list goes on. At one time every eighth grade science lab in the country had little asbestos squares for the students to put gas burners on. This is why there is so much asbestos exposure in our post-war industrial society, and why many mesothelioma patients say they were never exposed to asbestos — they are still thinking of the barbecue mitts.