Asbestos is a group of natural mineral fibers that are known for their strength and fire-resistant properties. Asbestos has been used in thermal insulation and fire proofing for the construction industry. Although asbestos fibers come in blue, brown, and green colors, most asbestos used in the United States is white asbestos, and is called Chrysotile.
The word asbestos is derived from a Greek adjective meaning inextinguishable. The “miracle mineral,” as to be referred to by the Greeks, was admired for its soft and pliant properties, as well as its ability to withstand heat. Asbestos was spun and woven into cloth in the same manner as cotton. It was also utilized for wicks in sacred lamps. Romans likewise recognized the properties of asbestos and thought they cleaned asbestos tablecloths by throwing them into the flames of a fire.
From the time of the Greeks and Romans in the first century until its re-emergence in the eighteenth century, asbestos received little attention or use. It was not available in large amounts until extensive deposits were discovered in Canada in the nineteenth century (late 1800’s). Following this discovery, asbestos emerged as insulating component in thermal insulation for boiler, pipes and other high temperature applications and as a reinforcement material for a variety of products; including stucco, plaster, floor tile, and roofing.
1. Types and Physical Characteristics of Asbestos
Asbestos is a naturally occurring mineral. It is distinguished from other minerals by the fact that its crystals for long, thin fibers. Deposits of asbestos are found throughout the world. The primary sites of commercial production are: the Commonwealth of Independent States, Canada, China, Brazil, Zimbabwe, and South Africa. Asbestos is also mined commercially in limited quantities in the United States, in California and Vermont.
Asbestos minerals are divided into tow groups – serpentine and amphibole. The distinction between groups is based upon a mineral’s crystalline structure – serpentine minerals have a sheet or layered structure, amphiboles have a chain-like crystal structure.
Chrysotile, the only asbestos in the serpentine groups, is the most commonly used type of asbestos and accounts for approximately 95% of the asbestos found in buildings in the United States. Chrysotile is commonly known as “white asbestos,” names for its natural color.
Five types of asbestos are found in the amphibole group. Amosite, the second most likely type to be found in buildings, is often referred to as “brown asbestos.” As you might assume, in its natural state Amosite is brown in color.
Crocidolite, “blue asbestos” is also an amphibole. Crocidolite was used in high temperature insulation applications.
The remaining three types of asbestos in the amphibole group are: anthophyllite, tremolite, and actinolite. The varieties are of little commercial value. Occasionally they are found as contaminants are asbestos-containing materials. Once extracted from the earth, asbestos containing rock is crushed, milled (ground) and graded. This produces long, thread-like fibers of material. What actually appears as a fiber is an agglomeration of hundreds of thousands of fibers, each of which can be divided even further into microscopic fibrils.
2. Uses of Asbestos:
Asbestos has been used in literally thousands of products. Collectively, these are frequently referred to as asbestos-containing material (ACM). Asbestos gained wide spread use because it is plentiful, readily available, and low in cost. Because of it unique properties – fire resistance, high tensile strength, poor heat and electrical conductivity, and being generally impervious to chemical attacks – asbestos proved well-suited for many users in the construction trades.
One of the most commons uses for asbestos has been as a fireproofing material. It was sprayed on steel beams; columns and decking that were used in construction of multi-storied buildings. This application prevented these structural members from warping or collapsing in the event of a fire. Chrysotile was the most commonly used asbestos constituent in spray –on fireproofing. Asbestos comprised 5 to 95 percent of the fireproofing mixture and was used in conjunction with materials such as vermiculite, sand, cellulose fibers, gypsum and a binder such as calcium carbonate. These materials are soft and may be fluffy in appearance and to the touch. They vary in color from white to dark grey; occasionally they have been painted or encapsulated with a clear or colored sealant. The material may be exposed or concealed behind a suspended ceiling. Application to structural members (beams and columns) often resulted in some material being sprayed on walls and ceilings as well. This referred to as a overspray.
Asbestos is added to a variety of building materials to enhance strength. It is found in concrete and concrete-like products. Asbestos-containing cement products generally contain Portland cement, aggregate, and Chrysotile fibers. The asbestos content may range up to 50 percent by weight depending on the use of the product. Asbestos cement products are used as siding and roofing shingles; as wallboard; as corrugated and flat sheets for roofing, cladding, and partitions; and pipes. Asbestos has also been added to asphalt, vinyl and other materials to make products like roofing felts, exterior siding, floor tile, joint compounds, and adhesives. A report issued by the U.S.
As an insulator, asbestos received widespread use for thermal insulation and condensation control. It was usually spay applied, trowel applied, or factory installed on or within equipment. Asbestos proved valuable as a component of acoustical plaster. The material was applied by trowel or by spraying on ceilings and sometimes walls. It varies in color. Similarly, as a decorative product, asbestos was mixed with other materials and sprayed on ceilings and walls to produce a soft, textured appearance.
The U.S. Environmental Protection Agency (EPA) distinguishes between friable and non-friable forms of ACM. Friable ACM contains more than 1% asbestos and can be “crumbled, pulverized, or reduced to powder by hand pressure when dry”. Other things being equal, friable ACM is thought to release fibers into the air more readily, however, many types of non-friable ACM can also release fibers it disturbed.
EPA identifies three categories of ACM used in building:
Surfacing Materials – ACM sprayed or toweled on surfaces (walls, ceilings, structural members) for acoustical, decorative, or fireproofing purposes. This includes plaster and fireproofing insulation.
Thermal systems Insulation – Insulation used to inhibit heat transfer or prevent condensation on pipes, boilers, tanks, ducts, and various other components of hot and cold water systems and heating., ventilation, and air conditioning ( HVAC) systems. This includes pipe lagging; pipe wrap; block, batt, and blanket insulation; cement and “muds;” and a variety of products such as gaskets and ropes.
Miscellaneous Materials – Other, largely non-friable products and materials such as floor tile, ceiling tile, roofing tile, concrete pipe, outdoor siding, and fabrics. While it is often possible to “suspect” that a material or product is or contains asbestos by visual determination, actual determinations can only be made by instrumental analysis. The E.P.A. requires that the asbestos content of suspect materials be determined by collecting bulk samples and analyzing percent and type of asbestos in the bulk material.
However, some of these materials do not have to be inspected and inventoried under Asbestos Hazard Emergency Response Act (AHERA) Rule. Under AHERA, asbestos- containing building materials (ACBM) in schools (Kindergarten through grade through 12) do not include materials installed outside of a building (e.g., roofing felt and siding). Likewise, under the Asbestos School Hazard Abatement Reauthorization Act (ASHARA), which applies to public and commercial buildings, the inspection of exterior ACBM is not required.