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How Asbestos Released into the Air on 9/11

When the North and South towers of the World Trade Center fell the morning of Sept. 11, 2001, the lives of 2,753 people were lost. A massive cloud of debris, chemicals, soot and more engulfed the lower Manhattan area following the collapse. It left layers of fine gray powder on every surface it touched, which was dubbed “WTC dust” by some researchers. This dust contained harmful materials like asbestos that cause cancer.

Many people who spent time near Ground Zero developed illnesses over the years. These include cardiovascular disease, respiratory issues and cancers such as mesothelioma.

The animations below illustrate how the toxic cloud spread in the minutes, hours and days after the collapse of the Twin Towers. They also reveal how asbestos was used in the original construction of the World Trade Center.

The Toxic Cloud Created at Ground Zero

Graphic showing what caused toxic clouds at Ground Zero

The speed and power of each tower’s collapse immediately created and dispersed this noxious cloud. The weight of the 110-floor buildings collapsing disintegrated the majority of each building’s mass into a dense dust cloud. This dust settled on the streets and structures throughout lower Manhattan. It took only 10 seconds for each tower to fall.

Made vulnerable by the impact of the hijacked airplanes, the exterior structure of the buildings initially held. But after remaining upright for almost two hours, the heavy upper floors began to collapse straight down. To illustrate the immense weight involved, one scientific researcher noted, “The mass of the upper block in the North Tower [that collapsed onto the floors below it] was the equivalent to the mass of the Titanic.” 

What Was in the Toxic Dust?

The composition of the WTC dust was a highly alkaline mix. It had pulverized glass and concrete, gypsum from drywall, asbestos fibers, steel and cellulose from paper.

The intense fires that brought the towers down continued to smolder at Ground Zero until Dec. 14, 2001 — over four months after the attack. The longevity of these burning fires led to toxic soot constantly being added to the contaminated air, releasing high levels of dioxin. A 2007 EPA analysis of Ground Zero noted that researchers had recorded “the highest ambient measurements of dioxin ever recorded anywhere in the world.”

In 2018, the World Trade Center Health Program created an “inventory of 9/11 agents,” which officially categorizes more than 350 9/11-related hazards that may have been present at the disaster areas. It identifies asbestos on the list and breaks it down a bit further by including two subvarieties of asbestos: chrysotile and Libby amphibole.

How Far Did the Dust Travel?

Graphic showing how toxic clouds spread in Ground Zero

Researchers determined that the plume shot up nearly a mile into the sky. It then spread out 44 miles above all of Manhattan and drifted across the East River into Brooklyn. 

An Environmental Protection Agency found it reached the Empire State Building three miles away. After the dust initially settled, it could easily still be recirculated back into the air and then carried even farther on the wind. 

The contamination dangers of carcinogenic matter in the plume decreased with time and distance. The greatest risk of suffering health consequences was most likely to happen within an immediate 1.5-mile radius of Ground Zero. 

Impact of Weather on Toxic Dust Exposure

The amount of moisture in the air can be a factor in identifying the conditions to remove toxic dust safely. The morning of 9/11 featured low humidity, so it was easy for the dust to be blown around. 

When rain came to New York City on Sept. 15 and again on Sept. 24, the downpour kept the dust saturated so it couldn’t become airborne again. Clean-up crews at Ground Zero would regularly water down the site on nonrainy days in an effort to keep the dust on the ground so it couldn’t spread farther with a breeze or other disruption.

How Much Asbestos Was Present in the WTC Buildings?

Graphic explaining why asbestos was used when building the World Trade Center

Asbestos was a popular addition to building materials from the 1940s through the 1970s. It was only natural for it to play a major role in the infrastructure of the World Trade Center. Known for its fiber strength and heat resistance, asbestos was often used in insulation and fire retardants. 

As the World Trade Center was constructed, asbestos was applied to the extensive steel beam infrastructure as an insulator and fire retardant. The North Tower, in particular, was built with hundreds of tons of asbestos-laced structural elements up to the 40th floor. 

When the planes hit each building at over 500 mph, the power of the impact actually shook loose much of the asbestos fire retardant that protected critical structural steel beams and trusses. The fires that ignited upon impact spread through the building swiftly in large part due to the 6,000 pounds of jet fuel that poured down through the structure. With the flame retardant no longer in place and the fire’s temperatures surpassing 1,500 degrees Fahrenheit, the steel support beams couldn’t withstand the heat. They began to buckle, leading to the collapse of each building. 

Health Impacts of Toxic Dust Exposure

Graphic explaining what was in the toxic dust in Ground Zero

Within weeks of 9/11, doctors at Mount Sinai Medical Center estimated that almost half of the Ground Zero cleanup crews were suffering from what The New England Journal of Medicine called the “World Trade Center cough.”  

The cough seemed to occur in those who had inhaled a lot of the dust. The size of the particulates within the dust varied, anywhere from a millimeter down to a nanometer in width. The tiny size was the perfect fit to embed deep in the lungs if inhaled. High concentrations of gypsum and calcite, both remnants from the crushed drywall and cement, easily irritated the mucus membranes of the eyes, nose and throat.

Asbestos exposure can take decades to reveal itself in the form of related cancers. The latency period for mesothelioma is 20 to 60 years, meaning that some of those exposed at Ground Zero may only now be showing symptoms of the rare form of cancer.

The unprecedented toxic cloud of dust and debris from the Sept. 11 terror attacks is still impacting lives today. Health dangers, such as asbestos-induced cancers caused by the collapse of the Twin Towers, affected people at or near Ground Zero and those located many miles away. As of 2022, 5,230 first responders — including firefighters, police officers and medical personnel, survivors and work crews — have died since that fateful day as a result of their exposure. This far surpasses the number of people who died on the day of the attacks.