Friday, November 13, 2009

A (Not So) Brief History of Asbestos

A somewhat rather indispensable and somewhat unhealthy building block of our modern civilization, has our current industry completely weaned itself from asbestos?

By: Ringo Bones

There are probably only a few times in our history where the health risk of asbestos produced a significant outcry to have it banned from everyday use. One was way back in 1973 when researchers at Mount Sinai Medical Center in New York established a link between mesothelioma – a rare form of lung cancer – and workers with long-term asbestos exposure. And the other one was the September 11, 2001 terror attacks on the World Trade Center towers highlighting the dangers of old buildings built before the ban on asbestos for architectural use was fully embraced. Even the United Nations headquarters in New York are one of the few remaining buildings containing large amounts of asbestos in its structure. Even though we managed to drastically wean ourselves from asbestos (it wasn’t easy by the way) in such a short period of time, looking back to the history of its use, one could conclude that our present almost asbestos-free technological society would certainly never have happened.

Asbestos is - or was - very useful in our long march to achieve our present state of technological prosperity. Asbestos was known in ancient times. Pliny the Elder even wrote about shrouds of woven asbestos used in the cremation of the nobility. Pausanias’ “Tour of Greece” describes a lamp wick not consumed by flame as being made “Carpasian Linen” a cloth of mineral fiber from Carpasius a district in Cyprus. Plutarch also recorded “perpetual lamp wicks” in the temples of the vestal virgins. Charlemagne is fabled to have amazed guests by tossing an asbestos tablecloth into the fire to be cleansed - While Marco Polo reported a working mine and an asbestos cloth manufacturing facility in Central Asia. The modern asbestos industry began with the working of an Italian mine in 1868. And the large-scale industrial production began with the discovery of asbestos in Quebec, Canada. Thanks to our search for a better steam engine.

Unlike other man-made products that were later on found out to be serious carcinogens, asbestos is neither man-made nor derived via the chemical processing of crude oil. It occurs as a natural mineral. Asbestos occurs in the form of veins and lenses within rock bodies as a byproduct of geologic metamorphism. And there are two main types of asbestos minerals, namely: serpentine and amphibole. Quite ironic for a serious environmental pollutant that is 100% natural.

Serpentine asbestos is also known as chrysotile whose chemical makeup is a hydrated form of magnesium silicate. Chrysotile makes up about 95% of the asbestos commercially mined making it the most important variety in terms of extraction and usage. Its fibers are of superior length, flexibility, fineness, and tensile strength. Chrysotile is found in rock as lustrous greenish veins. Its fibers are so fine that a single pound of this mineral provides almost six miles of asbestos thread. The fiber has a tensile strength that equals some grades of steel – i.e. 80,000 to 100,000 lb. per sq. in. Chrysotile asbestos possesses excellent resistance to heat, but turns progressively more brittle as temperature rises to about 400ÂșC.

Amphibole asbestos varieties that are commercially useful are crocidolite, anthophyllite, amosite, tremolite, and actinolite. Crocidolite asbestos is a soda-iron amphibolite and is also known as blue or Cape Blue asbestos because of its dull-blue color. Its fibers are of higher tensile strength (100,000 to 300,000 lb. per sq. in.) than those of chrysotile asbestos but crocidolite asbestos fuses at relatively lower temperatures.

Anthophyllite asbestos has a chemical makeup of magnesium-iron silicate type of asbestos that is composed of long coarse fibers of low tensile strength, while amosite asbestos is an iron-rich variation of the anthophyllite asbestos with a gray to brown color.

Tremolite asbestos, a calcium-containing magnesium silicate variant of chrysotile asbestos, is composed of fine silky fibers with a gray to white color. Tremolite asbestos is also the first form of asbestos that was widely used. While actinolite asbestos is a variant of tremolite asbestos where iron substitutes for as much as 2% of the magnesium in its chemical composition.

Asbestos is both quarried in open pits and mined in tunnels. The asbestos is initially removed manually from large pieces of quarried or mined rock matrix with the aid of a small hammer in an operation called cobbing. In later stages of the mining process, the asbestos fibers are removed from the crushed and screened matrix by air streams.

Crude asbestos is graded according to fiber length, fineness, flexibility, tensile strength, and infusibility. The longer fibers are carded and spun, sometimes with the addition of cotton thread. The spun fiber is woven into asbestos fabrics of varying thickness and densities. The smallest fibers, along with the rock dust from the matrix, are used to make asbestos cement. The amphibolite asbestos varieties all possess excellent resistance to chemical action, and are used to make filter pads and pipe-joint packing in chemical plants. They are also used as fillers in welding rods and plastics.

Asbestos board, a construction or insulating material is made of asbestos and portland cement molded into sheets by pressure. Asbestos paper is composed of thin sheeting of asbestos fibers bonded usually with a solution of sodium silicate. It is white, flexible and fireproof.

Belts of asbestos woven with fine brass wire are used as brake linings and to convey blast furnace slag, cement clinker, and other hot materials. Spun asbestos is made into fireproof ropes. Asbestos threads are woven into fireproof theater curtains and are also made into gloves for workers who must handle hot materials.

Given the myriad uses of asbestos in our modern technological society before it was banned in such a short period of time, it is quite a miracle that we even achieved a ban of over 90% when it comes to asbestos use. But with the looming threat of mesothelioma that first came to light in the early 1970s, the United States was among the first countries to achieve an almost total ban – greater than 90% - in the industrial and architectural use of asbestos. Even the visionary architects of the Sears Tower in Chicago decided not to use any form of asbestos during the start in its construction. After the preliminary reports of a rare form of lung cancer – i.e. mesothelioma – was uncovered by Mount Sinai Medical Center researchers during their study of workers exposed to high levels of asbestos fibers.

Given the health and environmental safety concerns of asbestos, there are even some towns in various isolated parts across the planet that were rendered as no-go areas after they were found out to contain too much free-floating asbestos particles. Such is the long-term legacy of our flirtation with asbestos – not to mention the probable long-term health concerns for workers involved in jobs with high asbestos exposure; Especially ship-breaking and working in old buildings with large amounts of old asbestos insulation.

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