Newsletter from the Asbestos Institute
Number 3, November 2002
Amid the general confusion and consternation that followed the collapse of the towers of the World Trade Center (WTC) after the attacks of September 11,2001, aphenomenal amount of false information circulated regarding how asbestos might affect theNew Yorkpopulation. Some organizations, such as the International Ban Asbestos Secretariat, quickly took advantage of the emotional climate to promote their interests without waiting for results from serious studies. They went so far as to say that the asbestos in the WTC building could result in more victims than the attack itself. Now thatU.S.society is slowly recovering from this catastrophe and reports on the fast collapse of the towers are being made available, citizens have a clearer idea of the role chrysotile played in protecting human lives. Certain assumptions were put forward, in particular that the intense heat resulting from the combustion of the burning aircraft fuel would have melted any type of insulation. However, data from laboratories and companies that deal with similar temperatures show that if the insulation would have stayed in place and had been applied in compliance with the standards, this temperature would not have been sufficient to melt the steel and cause the collapse. Other factors therefore explain the quick weakening of the structure.
The Facts
As with all buildings higher than 52 floors,U.S.construction standards require a minimum fire resistance rating of 4 hours for evacuation and setting up emergency measures. To accomplish this, the metallic structure, which acts as the skeleton for the tower, had to be covered with a product that keeps the heat from affecting the solidity of the steel. Steel loses 50% of its resistance at590°Cand melts at870°C. Unfortunately, the insulation used, that did not contain chrysotile fibres, was unable to meet this requirement since the South tower collapsed 47 minutes after impact, and the North tower collapsed in just under 104 minutes.
We have to remember that in the 1970s, the effects on the health of workers resulting from incorrect use of chrysotile, such as fireproofing, caused some administrations to stop using the product. The use of substitution products that were supposedly just as good was widely promoted. In the case of the WTC, the builder, the Port Authority of New York and New Jersey, had issued a directive prohibiting the use of powdered chrysotile in April 1970, when the towers were built. This is why no thermal insulation with this fibre was used above the 37th floor of the North tower or in the South tower, except in the elevator shafts. Remember that the airplanes hit above the 70th floor. The fire resulting from the combustion of aircraft fuel could not have exceeded 1020°C, a temperature high enough to melt the steel, but well below the point at which chrysotile crystallizes. Tests carried out by the American Society of Testing Materials (ASTM) show that formulas that did not contain chrysotile were applied less uniformly and that their resistance to marring was 10 to 25% lower than those with the fibre. In June 2002, before aU.S. government committee responsible for investigating the causes for the WTC catastrophe, a panel of architects and civil engineers also attributed the fast collapse of the towers to the lack of effectiveness of the insulating material as the main reason.
Worker Health Considerations
Use of all forms of powdered asbestos was very extensive in North America andEuropewhen skyscrapers were being built in the 1950s and 1960s. Unlike cement, which had been used before to protect metallic structures, mixtures containing various asbestos fibres made buildings considerably lighter and made it easier to create more innovative architectural designs. However, this method released significant quantities of breathable dust, which is harmful when inhaled in large quantities over extended periods. For example, Reitze [1972] had estimated that the number of breathable fibres in the work environment were 20 to 100 fibres per millilitre in a radius of20 metresfrom workers responsible for pulverization. Furthermore, at that time, there was very little or no respiratory protection for workers on construction sites.
Three types of thermal insulation were used during the construction of the twin towers:
1) A mixture of mineral wool, gypsum and Portland cement, to which a small amount of chrysotile (20%) was added for the first to 36th floors of the North tower. This mixture was used on the metallic structures and support beams.
2) An aggregate of vermiculite and gypsum was used on the interior surface of the outside wall. This mixture contained 13% chrysotile up to the 37th floor of the North tower.
3) A mixture of 80% chrysotile and 20% Portland cement was used in several locations where vibrations and air movement were high, such as in the elevator shafts.
The prohibition of using chrysotile in friable products was certainly a reasonable decision regarding workplace health at the time given the high exposure to breathable fibres. There have been many deaths attributed to exposure to asbestos, amphiboles and serpentine combined among workers responsible for applying asbestos-based insulation. But we do not know the harmfulness of products used as substitutes for chrysotile and whether use of substitutes may have made victims of the workers responsible for installing them. The only facts we have are that, on the one hand, the ineffectiveness of the substitute product is associated with the quick collapse of the towers and high number of victims and, on the other hand, the use of chrysotile as insulation may have been theoretically responsible for the deaths of two workers (1), but may have actually prevented the towers from collapsing.
Reflection and Conclusion
The prohibition of using chrysotile in friable products and therefore its installation, responsible for exposing workers to significant quantities of dust, was certainly a reasonable decision in terms of workplace health. But it appears that this decision was applied too quickly, before substitution products could be proven effective. In light of the tests carried out by the ASTM, if the insulating mixtures respected the safety standards in 1970, it is possible that time deteriorated them to such an extent that they no longer provided effective protection from fire at this temperature. Examinations of insulations with chrysotile in the structures of lower floors showed that they still had their initial characteristics. The decreased performance of substitution products is therefore the main reason for the collapse of the towers which, needless to mention, resulted in the deaths of just over 2,800 people. The unfortunate experience of the WTC towers brings us to reflect on substitution products. We have participated in an all-out offensive on behalf of multinational manufacturers of substitution products for several years, with the support of interest groups such as the International Ban Asbestos Secretariat, to quickly replace products containing chrysotile asbestos. Substitution is proposed without knowing the quality or innocuousness of substitution materials, based solely on the fact that asbestos is harmful to health. This is clearly an economic war in which business issues come before the health and safety of people. A series of other factors must be considered, based on risk analysis, before confirming that the substitution is a benefit for society. In many countries today, entire populations are deprived of drinking water and decent housing because chrysotile substitution products, that are forcibly imposed, are not of equal quality, cost more and pose health risks. However, contrary to the WTC, this deplorable situation continues in silence.
(1) For a detailed analysis, see article "The World Trade Center Catastrophe: Was the Type of Spray Fire Proofing a Factor in the Collapse of the Twin Towers?" article, Indoor Built Environment 2001; 10 : 350-360.
