Asbestos was a miracle material, virtually impervious to fire. But as we fixed city fires in other ways, we came to learn about its horrific downsides.
Few materials fell from grace like asbestos. Once cherished as an almost-magical material, it is now the archetypal carcinogen. We spent over a century integrating it into buildings, wiring, pipes, brake pads, and more, and we now spend billions of dollars a year removing it.
But the standard story of asbestos as a mistake – or even a crime – of massive proportions does not do justice to the real benefits it brought. Asbestos was central to mitigating urban fires, which cost thousands of lives each year as modern cities grew larger, denser, and more flammable. But as we learned to control urban fires without it, asbestos’s health costs seemed less and less worth bearing. Asbestos is in its final days and soon the material will almost disappear entirely.
Miracle materials are not all manmade. Asbestos is a family of six naturally occurring silicates, made from the same elemental blocks as sand or glass, organized in delicate fibrous strands that tease apart like cotton candy and compare with steel in tensile strength. Chrysotile or white asbestos, the commercially dominant form, is a serpentine silicate, with fibrous strands that crumble to the touch; the remaining five are amphiboles (including crocidolite, blue asbestos), spiky forests of short and fragile needles. In all its forms, asbestos has remarkable properties: it’s light, waterproof, and, most famously, fireproof.
The unique structure of asbestos requires a unique set of circumstances to form. The fibers of asbestos are crystals precipitated out of a solution of minerals in hot water under pressure. This is hydrothermal synthesis, a process used to grow artificial crystals in laboratory settings (or candy from syrup). The low-silica rocks in which asbestos originates are found naturally across the planet, and asbestos has been found and mined on every inhabited continent.
The first written record of asbestos was by Theophrastus, who categorized it correctly by including it in his mineralogical work, On Stones. He did better than most, considering that an animal origin for asbestos was a common misconception in the ancient world: asbestos was credited to everything from phoenix feathers to the mythical salamander to Princess Bride–style literal volcano-dwelling fire rats.
Its rarity and invulnerability to fire gave asbestos an air of mystique and an association with power. Charlemagne is said to have had a tablecloth of pure asbestos that he would throw into the fire as a party trick, and Emperor Ashoka of India sent a gift of asbestos cloth to Sri Lanka. Earnest pilgrims into the Holy Land were sold pieces of asbestos cloth as remnants of the Holy Shroud, made credible by their immunity to fire. Benjamin Franklin paid for his time in Europe by selling an asbestos purse to a collector (for which he was paid ‘handsomely’). Yet asbestos existed only as an interesting novelty without a clear use.
That use case came into being in the late nineteenth century. The fast-growing cities of the time were exceptionally flammable, with densely clustered buildings full of wood, fabric, and open flames. Electrification was new; fire codes were yet to become ubiquitous (or stringently applied). In some cases, even roads were made of timber.
Unsurprisingly, ‘Great Fires’ struck virtually every major city. Theaters, full of flammable set elements and a tightly packed audience, were a frequent source of fire. The risky productions themselves did not help – 31 of the 1,108 theater fires documented worldwide between 1797 and 1897 were started by fireworks on the stage.
Theater fires started mostly on the stage and then spread to the audience. It was critical that the two areas be separated to protect the audience. Theater owners attempted to separate the stage and audience with heavy curtains of sheet metal, called ‘iron curtains’. Experiments on a scale model following a fire in Vienna’s Ringtheatre in 1881 showed their limitations. A fire on the stage would blow the hot metal curtain out onto the audience it was meant to protect, not only endangering them but also extinguishing the gaslights meant to light the way to safety. In other instances, the curtain could collapse onto the stage or fail to descend at all.
Engineers and regulators experimented with a diversity of materials for safety curtains, settling on asbestos. The 1903 fire at the Iroquois Theatre in Chicago led to an exemplary institutional response. The Iroquois supposedly had an asbestos curtain that failed to come down during the fire, but later investigation of the remnants of the curtain revealed that the curtain was mostly vegetable fiber. Following the fire, Chicago ordered all its theaters to be closed down immediately, while in New York inspectors went around setting fire to theater curtains, in search of dupes being passed off as asbestos by noncompliant ownership. The message now was clear: asbestos, or nothing.
Theaters were not the only place where fires were common. Movie theaters, schools, hotels, hospitals, ships, and ports all existed under the threat of fire. Asbestos was gradually introduced in each.
Ports were particularly keen on fire safety. A fire port-side could easily spread among ships and destroy them, as it did famously in the 1900 Hoboken Docks fire in New Jersey. A fire that started in bales of cotton stored on a pier spread with the wind to stores of flammable turpentine and oil, which exploded in quick succession. Within 45 minutes, the fire had destroyed three piers and three major transatlantic liners belonging to the Norddeutscher Lloyd shipping company, and claimed over 200 lives. Navies and merchant navies were eager and early adopters of asbestos. When Norddeutscher Lloyd finally rebuilt the pier, asbestos felt was among the materials used.
The first mass-produced asbestos products in the United States were gas fireplaces, eventually joined by protective suits for firefighters and materials for roofing, felting, and boiler insulation. Asbestos became the standard material for applications as diverse as brake pad linings and insulation for electrical wiring. In the case of brake pad linings, asbestos was the only reliable material until well into the 1940s, and remains one of the few permitted uses in the United States today. Scientific American wrote in 1919 that ‘new uses of this material are being found almost daily’.
Production kept pace: prices fell from $128 per ton to $30 per ton in the United States from 1890–1904 following the discovery of commercially viable deposits in Canada and improved methods of refinement and transport. It was rapidly becoming price competitive in construction in the form of roofing tiles and in products where it could be blended with cheaper material, as in asbestos stucco and asbestos-cement shingles. One particularly clever product was asbestos paint, which made wooden structures flame-retardant. Patented in 1878, it was already on federal buildings, including the US Capitol, by 1879.
Asbestos became more important than ever in World War II. It was classified as a critical material by the US War Production Board, and its scope expanded from its traditional roles of fireproofing, friction reduction, and insulation to substituting other materials that were even more desperately needed elsewhere. It became the material of choice for aircraft hangars and ordnance stores, military prefabs, ductwork, and even common gutters and downspouts. Soon, conservation orders were issued limiting its use and privileging defense applications.
The Navy was at the forefront of asbestos use. Shipboard fires engulfed vessels that had limited means of fire suppression. Newer classes of ships such as the Essex featured asbestos curtains and fire doors, and no ships were lost to fire after 1942. In later years, as many as a third of all asbestos-related cancer cases in the US would be linked to US Navy ships or shipyards.
The postwar era combined a heightened awareness of the risk of fire with a massive wave of new construction. Asbestos was cheap enough to use in every building. America produced and imported asbestos at a fantastic rate. Asbestos consumption tripled between 1940 and 1950, increasing from 240,000 metric tons to 400,000 metric tons from 1940–1941 alone. At one point, as many as 4,000 products contained asbestos, including toothpaste. Things would soon change.
As early as 1898, factory inspectors noted the effects of asbestos on workers who breathed in its fibers, with one going so far as to call it ‘the evil dust’ (safety reports were a lot more colorful then). A 1918 report to the US Bureau of Labor Statistics, ‘Mortality from Respiratory Diseases in Dusty Trades’, explained that ‘in the practice of American and Canadian life insurance companies asbestos workers are generally declined on account of the assumed health-injurious conditions of the industry’.
In 1924, Nellie Kershaw, a 33-year-old British asbestos spinner, died. The inquest concluded that the cause of her death was suffocation traced to profound scarring of her lung tissue from being lacerated with microscopic asbestos fibers. The coroner who led the inquest called it ‘asbestos poisoning’. Her employer, the largest asbestos factory in the world and the owner of asbestos mines in Canada and South Africa, rejected the report.
Nellie Kershaw’s death was not entirely without consequence. The coroner pressed on, publishing his results in The British Medical Journal. Kershaw’s illness now had a name – asbestosis – and a British government survey of the asbestos industry in 1930 found that a quarter of all workers were suffering from it. The next year, Britain passed Asbestos Industry Regulations, 1931, the world’s first regulation dealing specifically with asbestos.
That did not immediately put a stop to asbestos, even in the United Kingdom. The event that finally did set off a wave of asbestos bans across advanced economies came over 30 years later, at a conference convened at the New York Academy of Sciences in 1964.
This conference was organized by Irving J. Selikoff of New York’s Mount Sinai Hospital. Selikoff had spent years interviewing workers involved with asbestos, among them asbestos weavers, pipe insulators, and shipyard workers. He later published results in 1965 and 1968 that suggested asbestos might be a carcinogen, but at the 1964 conference, he may have had his greatest impact by catalyzing the conversation in the first place. The conference itself was largely a consolidation of already available knowledge and presented little that was new or surprising, but the momentum it generated made a definite difference, and in the case of Selikoff, enemies.
Asbestos use collapsed in the wealthy world almost as dramatically as it had risen. The bans took off, slowly, in the early seventies. Denmark was first, banning asbestos for insulation and waterproofing in 1972. Sweden followed with a ban on asbestos spraying in 1973. The first total ban came in 1980, with Denmark again leading the charge. Each successive decade saw more jurisdictions join in restricting the use of asbestos, partially or fully, for the first time: eight more in the 1980s, 24 in the 1990s, and 36 in the 2000s. The bans were augmented with requirements to remove asbestos where found in existing buildings. As the threat of fire dwindled, Asbestos prohibitions spread.
Asbestos is now banned in at least 66 countries, including all members of the European Union, the United Kingdom, Japan, Australia, and South Africa. The United States is often cited as a rare industrialized country without a total ban, but it was no laggard in pursuing restrictions, either. The first American restriction came in 1973, followed in quick succession by further restrictions in 1975, 1977, and 1978. An effort by the Environmental Protection Agency to ban asbestos completely in 1989 was the closest the United States came to a complete ban on asbestos. In 1991, a Federal appeals court overturned provisions of the ban that would have come into force in 1993 and 1996, effectively protecting asbestos use in brake drum linings, roofing and flooring felt, and asbestos tiles. Despite this, the popularity of asbestos in the United States continued to fall.
The move against asbestos in the United States was globally consequential. The United States had traditionally imported nearly all of its asbestos and was the largest asbestos importer in the world. In 1970, the United States had imported close to 590,000 metric tons of asbestos; in 2000, this had collapsed to below 15,000 metric tons. Global trade in asbestos fell from 2.4 million to 1 million metric tons between 1970 and 2000, and the United States was responsible for 40 percent of this decline in volume.
Substitutes have been found for most applications. The majority of substitutes are natural or synthetic fibers that are not considered carcinogenic. Asbestos has been replaced in fiber-reinforced cement by cellulose fibers, in insulation by fiberglass and mineral wool, and in clothing by aramid fibers.
Elsewhere, its unique confluence of useful properties has proved harder to replicate. Asbestos cement, which was used to make cheap, durable pipes and prefabricated sheets for wall cladding, was by far the biggest use of asbestos, accounting for 80 percent of asbestos production in 1988. A particularly interesting niche where asbestos persists is in the production of chlorine. Asbestos diaphragms are used in the chlor-alkali process, the dominant technology for manufacturing chlorine, to separate the anode and cathode of an electrolytic cell. An alternative method uses polymer membranes instead. These methods have traditionally been considered ‘low concern’ from a health and safety standpoint; some researchers now suggest that we should be more concerned, but switching to the alternative method is expensive.
The economic case for asbestos slowed its decline in many places. Canada’s exit was particularly protracted, given its former status as a leading producer. The costs of damages and litigation, over $70 billion in the United States alone, have resulted in widespread bankruptcies of asbestos manufacturers and closures of asbestos mines. The last asbestos mine in Canada, which was also the world’s largest, discontinued operations in 2011. While Canada ceased mining, a ban on export did not come into force until the penultimate day of 2018. The town of Asbestos, Quebec, home to that final mine, abandoned its name in 2020.
The costs of abatement have been just as significant. That asbestos is implicated in asbestosis (limited mostly to workers with direct exposure, such as Nellie Kershaw) and mesothelioma (cancer of the mesothelium, which forms a lining around the lungs) is universally accepted. What’s controversial is the benefit from removing asbestos from all structures, given the risk to building occupants tends to be low. It is instead people who work directly with high concentrations of asbestos – such as shipyard and textile workers – who are at high risk.
The Environmental Protection Agency estimates there are over 700,000 public and commercial buildings in the US that contain asbestos, as well as 45 percent of the nation’s 100,000 schools. The number of residential buildings that contain asbestos is simply not known. Rachel Maines, the author of Asbestos and Fire, figures essentially every building constructed in the twentieth century prior to 1980 contains it. The requirement to remove asbestos in the built environment wherever found, so-called “in-place” asbestos, has given rise to an abatement industry in the United States with annual revenues already exceeding three billion dollars. These are expensive projects, where a consultant must be retained, workers must wear protective gear, and the worksite must be isolated with negative pressure.
The cost of such abatement at a national scale would likely run into hundreds of billions of dollars, for uncertain benefits. Asbestos is dangerous only when inhaled, and it cannot be inhaled except as airborne fibers that are released when asbestos is disturbed. Since abatement takes the form of ripping or scraping off asbestos from the places where it is found, it generates clouds of airborne fibers where there were none, and needs to be disposed of very carefully by abatement workers.
While the health consequences of removing asbestos are not yet fully understood, there are not currently reasons to be concerned. And natural sources of asbestos can confound data. For example, a large study using data across California found that the odds of developing mesothelioma declined by 6.3 percent for each ten kilometers of distance from the nearest source of environmental asbestos. If members of the ‘control group’ in a study, who are assumed to have no exposure to asbestos, actually had natural exposure to asbestos, researchers would underestimate the harms they face and the risks of further exposure to asbestos in occupational work.
How many lives did asbestos itself save in the final reckoning, net of the deaths it caused? It’s impossible to say. This is what we know: Fire deaths fell by over 90 percent in the United States over the twentieth century; asbestos was present in thousands of applications as a fire retardant; and without effective brake pads, the roads would have been much more dangerous. However, at the same time that asbestos became ubiquitous, fire codes matured, firefighting technology improved, and the insurance industry laid down stringent requirements for coverage.
There are common-sense compromises that sit between complete complacency and abatement regardless of cost. New York City Local Law 76/85 required asbestos to be removed in the cases of demolitions and renovations, but did not call for it to be removed proactively from all places where it existed. Theater remains an iconic industry in New York City, and many theaters continue to have asbestos curtains.
The same calculus features in global attitudes toward asbestos. Even as the developed world has abandoned asbestos, others have expanded their production. The two leading producers are Russia and Kazakhstan, which have built upon Soviet-era operations to account for over 83 percent of all exports. The market is similarly concentrated on the importers side as well – the three largest importers of asbestos account for over 65 percent of all imports, and the top ten are all in Asia. Russia is itself a major consumer, in third place behind China and India.
India, where asbestos is called ‘the poor man’s material’ and asbestos roofs are an alternative to safer, but more expensive, tin or fiberglass roofs, is also beginning to move away from asbestos. The country banned the domestic production of asbestos in 1986, but not its use, becoming the largest importer of asbestos in the world by 2003. In 2011, the Supreme Court of India denied a public interest filing to ban asbestos, favoring continued regulation by states instead. In 2018, the western state of Maharashtra forbade the inclusion of asbestos in regional development plans. The following year, the southern state of Kerala ordered the removal of asbestos roofing in schools.
The impact on trade figures has been slow but certain. The global trade in asbestos fell from over $500 million to under $300 million from 2012–2018, with India reducing imports by over $100 million, the most of any country. The next-largest importers, Indonesia and China, also cut down. As these countries grow richer, they too may soon decide that the costs of asbestos have come to outweigh its benefits.