R. Nolan, M. Ross, G. Nord, C. Axten,J. Osleeb, R. Wilson

R. Nolan, M. Ross, G. Nord, C. Axten,J. Osleeb, R. Wilson

ASSESSMENT OF RISK OF ASBESTOS-RELATED CANCER BASED ON AN ANALYSIS OF AIR AND SETTLED DUST SAMPLES FROM THE 9/11 ATTACK ON THE WORLD TRADE CENTER COMPLEX

Abstract

In the aftermath of the September 11th atrocity in New York City, which destroyed the Twin Towers, all the other buildings in the World Trade Center (WTC) complex and St. Nicholas Greek Orthodox Church, questions have been raised concerning the potential for health effects from the dust. The initial dust cloud caused a horrendously high particulate exposure, which was both brief and unforgettable. Twenty-four hours after the buildings collapsed the airborne concentration of dust was markedly lower but it remained uncertain if exposures to hazardous particles, particularly asbestos, would be elevated from background during the time required to remove the 1.5 million tons of building debris. This report will address the questions: What were the asbestos fiber type(s) and their concentration(s) in the air? How can analysis of settled dust inform us about early asbestos exposures, both on 9/11 and post 9/11, where air-sampling data are either non-existent or limited? How do the outside ambient airborne asbestos levels determined in Lower Manhattan post 9/11 compare with historical background levels of asbestos in NYC and elsewhere? What are the asbestos-related cancer risks as a consequence of the type of asbestos exposures, which occurred post 9/11?

Analysis by analytical transmission electron microscopy (ATEM) of representative settled dust collected in Lower Manhattan (five days post 9/11) found trace levels of chrysotile asbestos. No other asbestos fiber type was found to be present in any of the six settled dust samples. Ironically, the only bulk sample containing no asbestos was fireproofing removed from a piece of structural steel. Due to the enormous amount of dust, containing trace levels of chrysotile asbestos, released into the ambient air of Lower Manhattan it is possible that persistent levels of airborne asbestos detectable above background could occur. To evaluate this possibility, six air samples were collected in October of 2001 to characterize the particles in the ambient air in Lower Manhattan starting twenty-seven days post 9/11. The goal was to determine the non-occupational exposures to the general population, not those with occupational exposure related to performing demolition and debris removal. The collection methodology and the microscopy analysis protocol for the air samples allowed for the examination of all the asbestos fibers in at least 10,000 ml of ambient air. The type of asbestos and size distribution could be determined.

No asbestos fiber (of any fiber type or length) was found in any air sample one month post 9/11. The mean ambient airborne asbestos concentration in Lower Manhattan was below 0.00008 f/ml. That was a level consistent with the background pre 9/11 for more than a decade in NYC. The airborne concentration of asbestos in NYC starting a month post 9/11 is consistent with what the World Health Organization (WHO) considers the low end of the background for asbestos in ambient air worldwide. This was markedly lower than the level of 0.01f/ml, that is usually regarded as safe. However, the initial exposures on 9/11 were undoubtedly high and probably remained elevated above background for some period of time during the next twenty-seven days. We will use risk assessment to determine the upper limit of any increased risk of the two principal asbestos-related cancers – mesothelioma and lung cancer – among the general population of Lower Manhattan, which might be associated with the asbestos released from the September 11th attack on the Twin Towers. The important variables determining these asbestos-related cancer risks are age at first exposure (mesothelioma), smoking (lung cancer), asbestos fiber type and cumulative exposure (intensity and duration of exposure to airborne asbestos).

Introduction

The target of the terrorist attacks on September 11th in New York City was the Twin Towers (WTC1 and WTC2) of the World Trade Center complex. Health concerns have been raised about the potential for asbestos-related cancer risk from the increase in airborne asbestos associated with the murderous 9/11 attacks. This report will describe the characteristics of representative samples of the settled dust released from the collapse of the Twin Towers and other buildings and ambient air samples. We collected the ambient air samples starting 27 days after the initial collapse, and during a time when there was still considerable public health concern about the risk of asbestos-related cancer in Lower Manhattan due to the 9/11 attacks. The type(s) and concentration(s) of airborne asbestos in the area surrounding the WTC site were determined and the cumulative exposures to the general population of Lower Manhattan due to the events of 9/11 were estimated; these are the important experimentally determined variables for the risk assessment.

As the removal of the debris took many months, any increase in the airborne asbestos concentration associated with the work could have conceivably led to a situation where the initial hygiene steps taken to control airborne asbestos exposures might prove to be inadequate. Possibly, allowing the general population, living near the WTC site in Lower Manhattan, to acquire a cumulative asbestos exposure (with an intensity and duration to a specific fiber type) that after a latency period of greater than 20 years, might lead to an increase in asbestos-related cancer among the area’s general population (Hodgson & Darnton, 2000, Nolan et al., 2001). On the basis of the specific asbestos fiber type(s) present and their post 9/11 concentrations in the ambient air, we will develop a risk assessment for asbestos-related mesothelioma and lung cancer.

Asbestos health hazards due to the events of 9/11 have been the focus of much media attention. However, little, if any, attention prior to this report has been given to undertaking the type of air sampling necessary to perform a modern asbestos-related cancer risk assessment specific for the cumulative exposure(s) and specific asbestos fiber type(s) caused by the 9/11 attacks.

History of the world trade center complex

The groundbreaking for North Tower (WTC1) was on April 4, 1966 followed by the erection of the structural steel starting in August of 1968. By the end of 1970 the first tenants had moved into the 110-story Tower (at 1,368-feet (ft) it was then the tallest building in the world) topped with a 360-ft transmitting antennae. By early 1972 the 110-story South Tower (WTC2) was completed with a height of 1362 ft. The ribbon cutting ceremony was held on April 4, 1973 (FEMA, 2002).

An additional five buildings would eventually be added to complete the complex – WTC3 a 22story hotel to the west of the South Tower (WTC1), WTC4 and WTC5 were two nine-story office buildings, WTC6 an eight-story office building and the final building WTC7 a 47-story office building across the street from the main part of the 16 acre complex was completed in 1985. The WTC complex contained 12,000,000-ft2 of office space (Fig. 1).

Events of September 11, 2001

The first hijacked Boeing 767-200ER out of Boston’s Logan Airport crashed into the north face of the North Tower (WTC1) between the 94th and 98th floors at 8:46AM with a second identical aircraft (also out of Logan) striking lower (between the 78th and 84th floors) on the south face of the South Tower (WTC2) just 17 minutes later. None of the 157 people aboard the two aircrafts survived the impact. Of the 58,000 people estimated to be in the WTC complex that morning approximately 14,000 were thought to have been in the Twin Towers when the first aircraft struck. Approximately 6,000 were below the impact floors in the North Tower (WTC1) (see FEMA 2002, for details of the event summary which follows).

Both towers sustained considerable structural damage, and both were severely rocked by the impact of the aircraft. It has been reported that on impact, the South Tower (WTC2) swayed in one direction for 7-10 seconds before swaying back, although dramatic to the tower occupants, the structural strength required for this motion was within the design envelope of either Tower. Each of the Twin Towers weighed about 500,000 t (or 3,650 times the mass of the Boeing 767-200ER) and had flexibility in the wind and viscoelastic motion dampers to minimize their movement, thereby reducing the risk of motion sickness to those occupying the high floors of the towers on windy days. Each tower was designed to withstand hurricane force winds of 135 miles per hour (MPH) (or about 5,000 t of lateral load). The damage caused by the impact of the aircrafts on a relatively low wind day (10-20MPH) was not sufficient to knock over or initiate a global collapse in either tower.

Fig. 1. The 7 buildings of the World Trade Center complex stood on 16 acres across West Street form the
World Financial Center (WFC). At the center of each tower was an 87-ft by 137-ft inner core which
differed in orientation between the two towers

All the sides of both towers had widths of 207 ft while the wingspan of the Boeing 767-200ER was 156 ft. The first aircraft flying south entered the impact face of the North Tower, at an angle and destroyed about 31 of the 36 steel supporting columns of the impact face over 4 stories resulting in a partial collapse of the local floors. The 274,000-lb aircraft was estimated to be traveling at 470 MPH and came to a complete stop within the footprint of the building. The building load was shifted to the remaining steel columns and the tower remained standing after an impact significantly beyond what could have been reasonably anticipated. The Twin Towers were the first buildings, other than those used by the military or for generating nuclear power, where impact by an aircraft was a design consideration. The initial fireball (estimated to have consumed 10 to 30% of the 10,000 gallons of fuel aboard the aircraft) was followed by an extensive fire initiated by the dispersion of the jet fuel in the air followed by the ignition of the fuel-air mixture. The sudden increase in the temperature created a pressure wave, which expanded the burning fuel into a fireball. This dramatic fireball grew slowly – taking 2 seconds – to reach its full size of approximately twice the width of the building. This relatively slow rate of expansion is not characteristic of an explosive device that was considered as a possibility when the fireball was first observed. The fires in each tower were producing between 35trillion BTU/hr with ⅓ to ½ of the heat being vented outside and driving the plume of smoke (Fig.2a).

The temperature of the fire was estimated to have a maximum of no more than 1,100C and the amount of heat generated was not sufficient to melt steel. However, the towers were not designed to have large numbers of sequential floors, each of 40,000 ft2, being on fire at once. The World Trade Center had specifications, which placed limits on the total combustibility of the contents of any floor; we take this specification as an indicator of the Twin Towers vulnerability to fire (NY Board of Fire Underwriters, 1975). The nature of the aircraft impact damage to the building prevented the two principal fire control tactics, water sprinklers and manual fire fighting, from being used to control the fire. On 9/11, the ability of the towers to maintain structural integrity after the initial impact was critically related to the fireproofing.

The Twin Towers were designed as rigid hollow tubes with both an inner and a perimeter steel structure. Behind the distinctive aluminum façade (19" wide windows set 22" apart) were the steel supporting columns of the perimeter. The architectural design, by Minoru Yamasaki and Associates, called for the Towers’ windows to be narrower than the width of a person’s shoulders and therefore reduce the possibility of anyone looking out from their great height getting a sensation of possibly falling. The horizontal floor trusses ran from the outer vertical steel columns to the 87-ft by 137-ft inner core, which carried the gravity load of the building in addition to housing 99 elevators, 3 exit stairways and 16 escalators (Fig. 1). The core was a key design feature of the towers eliminating the historical need for columns every 30 ft or so that would have formed a dense supporting grid on each floor. The connection between the inner and outer steel structures via the trusses was critical to the structural strength of the towers and creating the hollow tube, which made the large open floors possible. This innovative design created open 30,000-ft2 floors, which were a highly desired feature of the Twin Towers.

Although it was struck second, the South Tower (WTC2) was the first to experience global collapse at 9:59AM having stood for only 56 minutes after impact, with the North Tower (WTC1) following about 30 minutes later. The aircraft struck the South Tower on an angle to the right; largely missing the north to south oriented inner core and pushing the office furniture and other debris into the northeast corner leading to an intense localized fire (Fig. 1). A jet engine, landing gear and part of the fuselage of the doomed aircraft came out of that corner with some parts landing as far as seven blocks to the north of the South Tower (WTC2).

In addition to weakening the steel columns the heating may have caused the trusses to sag thereby placing a force on the four bolts securing the trusses to the steel columns for which their design provided little strength. Each tower’s structural stability was critically related to the floor trusses that strengthened the building by connecting the steel of the perimeter tube to the inner core, which was attached by four bolts on each end. The truss designs provided strength for shear forces and vertical load but not for the tension caused by the heated truss sagging. A second significant factor could have been the range in temperature along a piece of steel caused by the non-uniform fire. When a single piece of steel has temperature differences ranging up to 150 C or more at different points residual stress develops and weakens the steel. Although the photographic record, particularly of the South Tower (WTC2) provides much information, the nature of the damage will probably never be known in sufficient detail to provide definitive explanations for the global failure of both towers.

In the South Tower (WTC2) the most intense fire appeared to be on the 80th floor along the north face. A stream of molten metal (possibly aluminum from the aircraft) was seen streaming from an impact opening just prior to the tower’s collapse. The trusses breaking away from the steel columns in the perimeter may have triggered the collapse of the floor. This suggestion is supported by the observed cloud of dust blowing out the side of the building prior to the collapse of the outer wall in the northeast corner.

Once one floor collapsed, whatever structural strength remained in the damaged tower was insufficient to prevent a rapid global failure. At the time of the aircraft impact, approximately 2,000people were left in the South Tower (WTC2). Most (if not all) persons below the impact floors were evacuated safely while of the 500 estimated to be trapped above, only four survived.

Three factors are thought to be important with regard to the rapid collapse of the South Tower (WTC2): 1. The second aircraft was estimated to be traveling 120 MPH faster than the first plane (thereby increasing the kinetic energy of the faster aircraft by 50 % compared to the one striking the North Tower). 2. The damage occurred lower in the building making the overhead mass greater on the impact and fire damaged area. 3. The fire was particularly intense in the northeast corner, where the failure of the structural steel columns and trusses (weakened by a combination of both the heat and temperature ranges caused by the non-uniformity of the fire) may have initiated the global collapse.

The initiating event for the collapse of the North Tower (WTC1) is thought to be different from that of the South Tower. Here the damage to the inner core was more extensive due to the direct impact of the aircraft, which only traveled about 60-ft before striking into the inner core of the North Tower (WTC1). The damage to the inner core caused by the impact of the 274,000-lb aircraft traveling at 470MPH was likely to have been extensive (Fig. 1). The collapse of the North Tower seems to have been related to the failure of the other end of the trusses from the South Tower (WTC2). Perhaps damage to the inner core, which had been severely impacted by the aircraft and was burdened with carrying the significant gravity load of the tower, explains the different initiating mechanism for the global collapse of the second tower. The evidence for this inner core failure in the North Tower (WTC1) rests in part on the observation that the transmitting antenna began to fall prior to the collapse of the outer walls. Based on this observation the structural engineers speculate that the collapse of the North Tower (WTC1) was triggered by an inner core failure. This inner core failure led to 1,400deaths.