Respiratory Health Consequences Resulting from the Collapse of the World Trade Center

Posted on by Administrator

By guest blogger Dr. David Prezant of the World Trade Center Medical Monitoring and Treatment Program and the Albert Einstein College of Medicine*

See the introduction to this blog entry by Dr. Christine Branche.

Can respirators be redesigned to “work” in this environment?

On September 11th, 2001, terrorist attacks led to the collapse of the World Trade Center. Approximately 70% of the buildings’ structural components were pulverized in the fiery collapse of these towers, including six million cubic feet of masonry, five million square feet of painted surfaces, seven million square feet of flooring, 600,000 cubic feet of window glass, 200 elevators, and all other items present in a modern office complex.1 It is estimated that hundreds of thousands of people were exposed, with the most highly exposed group being the rescue, recovery and cleanup workers.2,3 Pulverized building materials predominated in the initial period post-collapse, while combustion-derived pollutants increased as rescue, recovery and cleanup progressed.4 The fires at the site created toxic combustion products, such as polycyclic aromatic hydrocarbons (PAHs), dioxins, volatile organic compounds, and various other known carcinogenic compounds.1,4,5,6,7 Contaminants such as asbestos, hydrochloric acid, PCBs (Polychlorinated biphenyls), silica and heavy metals were found in the dust and ash resulting from the WTC collapse.1,4,5,6,7

The WTC Cough Syndrome (a chronic cough syndrome, thought to be a consequence of upper and lower respiratory disease typically including chronic asthmatic bronchitis, chronic rhinosinusitis, chronic gastroesophageal reflux, or any combination of the three) has been reported by a large percentage of the exposed. Rarely, there has also been evidence of interstitial lung disease, such as sarcoidosis, pulmonary fibrosis, and bronchiolitis obliterans. The WTC Cough Syndrome was first described in rescue workers from the Fire Department of the City of New York (FDNY).11 Higher rates of upper and lower respiratory irritant symptoms have also been described in at least seven WTC rescue/recovery worker groups including firefighter, police officer and other rescue/recovery and cleanup workers.12,13,16,17, 18,19,20,21 Respiratory consequences have also been noted in WTC studies on community residents, children & office workers in lower Manhattan.3,22,23,24

Pulmonary function declines or abnormalities have been significantly related to WTC exposure intensity (based on arrival time) in FDNY and non-FDNY workers. This remained true even after accounting for pre-existent disease and/or cigarette smoking.11,13,25,26,27,28,29 For 12,079 FDNY rescue workers in the first year post-WTC, a significantly greater average annual decline in forced expiratory volume in 1-second (FEV1) of 372 ml was noted in the first year post-9/11/01 when compared to the normal annual decline of 31 ml found in the 5-years of pre-WTC testing—a substantial accelerated decline in pulmonary function.3 Similar findings were found for the forced vital capacity (FVC). In the NY/NJ consortium report on 8,384 non-FDNY workers/volunteers, 28% had abnormal pulmonary function test results13. They also found that a low forced vital capacity (FVC, a measure of lung capacity) was 5 times more likely among the non-smoking portion of their cohort than expected in the general US population (which includes smokers and non-smokers).13 Studies in both cohorts (FDNY and non-FDNY) are currently underway to determine the course of pulmonary function over the next 5 years post-WTC, specifically, whether it has improved, stabilized or declined, and, if there are differences in clinical course within or between the cohorts, and which factors might be predictive of favorable or unfavorable outcome.

A clear exposure-response gradient has been found. Numerous studies have documented significant associations between increased respiratory symptoms, persistent airways hyperreactivity, RADS or asthma, and/or declines in pulmonary function with earlier WTC arrival times.2,11,12,16,17,18,19,20,25,26,27,28,29,33 A recent WTC registry study on newly diagnosed (post-9/11/01) asthma in rescue and recovery workers also showed an effect of cumulative exposure (especially greater than 90 hours) even after controlling for initial dust cloud exposure and early arrival time.33 Occurrences of WTC respiratory disease in rescue workers/volunteers whose first exposure was more than 48 hours post-collapse could be explained either by “high-level” exposures generated by activities that disturbed dust in place, while entering enclosed, poorly ventilated areas, or by the accumulation of repeated “low-level” exposures over time.

The WTC registry recently reported that for rescue/recovery workers who arrived on 9/11/01 and worked in all subsequent time periods (n=2,161), use of masks or respirators did not eliminate the risk for newly-diagnosed asthma; but that delays in the initial use of a mask or respirator were associated with an increased incidence of newly diagnosed asthma.33 This risk was substantial, with a delay of 1 week associated with at least a 60% increase and a delay of 16 or more weeks being associated with a two to three-fold increased risk in newly-diagnosed asthma. Even higher risk ratios were found when the population was restricted to firefighters and other search/rescue personnel, suggesting a greater or different exposure.

Ninety-five percent of the respirable WTC dust was composed of large particulate matter (≥10 microns in diameter).1 Particles of this size have conventionally been thought to be filtered by the upper respiratory tract, rarely entering the lower respiratory structures.4 However, there are a number of reasons to expect lower airways also to be at risk from the dust cloud. First, it has been shown that alkaline dust impairs nasal clearance mechanisms, and most WTC dust samples had a pH greater than 10 (very alkaline).14 Second, the nasal filtration system is optimally functional during restful breathing. However, WTC rescue/recovery workers, as a consequence of their work activities (moderate to high level physical exertion), were breathing at high minute ventilations where mouth breathing predominates. Third, although only five percent of the WTC dust was smaller than 10 microns in diameter, the extraordinary volume of dust in the air meant that the respirable fraction (particles less than 10 microns) represented a significant amount of exposure. Finally, although only a small percentage of particles larger than 10 microns tend to impact in lower airways, the huge magnitude of the WTC dust cloud meant that a small percentage of particles that penetrated deep into the lung may have added up to a significant exposure.15 In fact, in a study of 39 firefighters from the Fire Department of the City of New York (FDNY) 10 months after exposure,15 it was demonstrated the WTC dust did make it down into the lower airways, as particulate matter (>10microns) consistent with WTC dust, with associated increases in inflammatory cells and cytokines in induced sputum.

Respirators were not available early on and were not used consistently even when available.26 This is in sharp contrast to the estimated 1.3 million U.S. workplaces (labs, hospitals, etc.) where respirators are used daily to provide protection against various airborne hazards. But few if any of these workplaces are disaster sites with critically time-dependent rescue operations underway. Respirators require fit-testing and prior health clearance which is not often immediately available for disaster rescue workers. They are uncomfortable for prolonged use and do not allow for necessary communication between co-workers in this potentially unsafe work area in which coordination of the activities of work crews was essential. Thus, even when available, there are significant barriers to the use of respirators in a disaster environment, especially when rescue efforts are underway.

Given these barriers to use of respirators during rescue efforts at disaster sites, we pose the following questions:

  • Are we certain that normal fit-testing procedures confirm that the respirator will fit correctly during moderate to heavy physical exertion?
  • How can we assure protection while maximizing comfort – essential for reducing barriers to wearing a respirator?
  • How can we assure protection, while maximizing the ability to communicate between workers, essential for maintaining safety in a hazardous environment?
  • Will no fit-test respirators be available in the near future?
  • What features of current respirator design need further improvement for this environment?
  • How have users (first responders, construction workers) from disaster sites been involved in the past and how will they be involved in the future in testing new respirator designs?
  • Do respirator manufacturers understand the needs of current and future users?
  • Are there barriers that prevent respirator manufacturers from responding quickly to user needs?
  • Are users looking for improvements for which technology does not yet exist?

—David Prezant, M.D.

Dr. Prezant is the Chief Medical Officer and Co-Director of the World Trade Center Medical Monitoring and Treatment Program in the New York City Fire Department and Professor of Medicine, Albert Einstein College of Medicine.


*The findings and conclusions in this report are those of the author and do not necessarily represent the views of the National Institute for Occupational Safety and Health.


Posted on by AdministratorTags

10 comments on “Respiratory Health Consequences Resulting from the Collapse of the World Trade Center”

Comments listed below are posted by individuals not associated with CDC, unless otherwise stated. These comments do not represent the official views of CDC, and CDC does not guarantee that any information posted by individuals on this site is correct, and disclaims any liability for any loss or damage resulting from reliance on any such information. Read more about our comment policy ».

    Since September 2001 I have maintained a free and confidential “9/11 list-serv”.

    The “9/11 list-serv” distributes daily e-mails containing newspaper articles and other relevant information re: 9/11 issues of interest to 9/11 families, 9/11 organizations and interested individuals.

    The 9/11 List-serv archives can be accessed at

    If you would like to ‘subscribe’ to this free news service – send an e-mail to amkorotkin @ with the word “subscribe” in the subject box.

    References to products or services do not constitute an endorsement by NIOSH or the U.S. government.

    I have read all about the top what have write… I only want know… until now 2oo8… still got hazard at the world trade centre? I mean around that collapse have happen? now long it can be hazard? or it maybe take long time like… boom at hiroshima? effect many people?

    Can answer me… I just wan know…. because I a safety and health student… how can hear the explaintion… thank

    The chemical name for “silica” is silicon dioxide. In miners, long term exposure to respirable crystalline forms of silica, such as quartz, can cause silicosis. This is a form of pulmonary fibrosis that typically affects predominantly the upper lobes and can also cause calcifications of the mediastinal/hilar lymph nodes. Depending on level of exposure, silicosis can either be chronic, developing more than 10 years after initial exposure, or accelerated, occurring within 10 years after initial exposure. Both forms of the disease are progressive even after removal from the work environment. Acute, massive exposure to silica dust can cause flooding of the lungs with protein-rich fluid within weeks to months of exposure. Affected people typically live less than 4 years after onset. This condition is called acute silicosis. These inhalational lung diseases are often related to crystalline silica dust exposure from mining or excavations. The term “amorphous silica” refers to silica that is not in a crystalline form. An example of non-crystalline silica would be pulverized glass created by building collapses. Long-term effects remain to be determined but there is enough evidence for pulmonary inflammation among those exposed to WTC dust that long-term monitoring is essential.

    Dr. Prezant,

    The following comments address your first two questions. They also concern a decision made during the WTC response that may affect how facepieces of air-purifying respirators are assigned to workers during future responses to similar disasters.

    An air-purifying respirator with an elastomeric half-facepiece was judged to be the most appropriate choice for the majority of WTC workers doing rescue, recovery, and clean-up activities. This choice was made after reviewing documented and potential airborne hazards; the physical characteristics of the site; physical demands on WTC workers; and the assigned protection factors, advantages, and disadvantages of all classes of respiratory protection. The most important and most variable attribute of this respirator is how well the facepiece seals to the face. Thus, facepiece fit-testing is essential for ensuring a secure and comfortable face seal. The exercises done during normal qualitative and quantitative fit tests should have been adequate for ensuring that properly selected respirators were protective during the physical demands of WTC activities.

    Thousands of air-purifying respirators were distributed at the WTC. OSHA has reported that they distributed respirators to 4,000 workers daily at the peak of recovery operations and more than 131,000 respirators in the ten months following the WTC attack. However, OSHA did not begin quantitative facepiece fit-testing until December 2001. Until then, selecting a facepiece for a worker was based on a facial analysis and fit checks. The decision to use this process might have been made because it could be completed more quickly than facepiece fit-testing.

    In 2002, NIOSH researchers learned that data on WTC workers had been compiled concerning the facepiece that a person was given initially and results of subsequent facepiece fit-testing. We had hoped that the data would provide an insightful comparison of the two methods used at the WTC to assign respirator facepieces, but no one was found who was willing to share this important information with us. If this information still exists, OSHA should be encouraged to study the data and report whether the facepieces of air-purifying respirators can be assigned safely in crisis situations simply on the basis of facial analysis and fit checks.

    How much would a possible pre-existing minor respiratory problem be worsened by exposure to the components of the collapsed building dust, or would new problems just arise because of the possible predisposition?

    Both new conditions and worsening of pre-existing conditions have occurred. For example, people exposed to dust created by the WTC collapse have commonly developed asthma-like symptoms, which can often be severe. This has happened to people who had pre-existing asthma and got worse. It has also happened as a new condition in people who had no previous history of asthma. The same situation applies to another common problem, upper airway problems like sinusitis. We don’t fully understand why some people have worse problems than others. We also don’t know if, over time, people who were heavily exposed to WTC dust will have an increased risk for additional problems to those already identified. That is why it is important that we continue to monitor the health of those who were exposed.

    Hello, my name is Mariah Stein and I am a graduate student at ODU in a Risk Assessment course. I found your article/blog very interesting and I have a few questions. The New York Fire Department was the first to respond, they are equipped with protective gear for job related use, without any prior experience to this sort of disaster response it was expected that they did not have the appropriate respirator available to them to minimize their risk of inhaling harmful dust particles. However in light of all the studies related to dust exposure and risk of respiratory effects; does the Fire Department of New York require its employees to wear a respirator when responding to disaster/rescue efforts under an “employer implemented respirator program”? If so, the program must be regulated by OSHA under Respiratory Protection Standards, 29 CFR 1910.134.

    Another question has to do with the availability of “emergency use respirators” to volunteer rescuers, now that disaster and anti terrorists’ plans have been established are there measures for providing some barrier of protection to these volunteers through “emergency use respirators” that do not require fit tests? The logic being that the protection offered by these emergency respirators may reduce the risk of respiratory problems as opposed to no protection at all; maybe a risk assessment should be done to ascertain the level of effectiveness associated with “emergency use respirators”. Also, in reading the article the question of communication was addressed when using a respirator. Being in the military, it wasn’t uncommon to remain in a gas mask for several hours (12) or more during training; our gas masks had speech transmission adapters. Why couldn’t the FDNY utilize these speech transmitters for their respirators to overcome the communication barrier?

    Thank you for your comment. This reply is a combined response from NIOSH and Dr. Prezant.

    Were the FDNY responders covered under an “employer implemented respirator program”?
    The responders from the FDNY as well as volunteer responders from other fire departments were equipped and trained with respirators which were selected, used and maintained as part of an employer-implemented respiratory protection program under OSHA’s Respiratory Protection Standards, 29 CFR 1910.134. However, because FDNY firefighters were equipped with SCBA respirators, they did not have adequate air supply to last more than 20 minutes. Normally, at fires this is either enough air or firefighters are rotated in and out of the fire scene or rarely, firefighters use additional SCBA air cylinders. However, since this was a major disaster, fresh cylinders could not be supplied. Furthermore, the nature of this work (rescue and recovery) made use of SCBA very difficult. The appropriate respirator (half-mask P100) was not immediately available.

    Should there be consideration given to make available “emergency use respirators” that do not require fit tests for use by volunteer responders at terrorist events? Should a risk assessment be done to ascertain the level of effectiveness associated with “emergency use respirators” worn without the benefit of fit testing?
    Loose-fitting, respirators that do not require fit testing to provide the expected level of protection that are approved by NIOSH are available, and could be used by volunteer rescuers. These respirators are designed with an airflow of filtered or clean air to the facepiece and directed into the wearer’s breathing zone. The units, which would be usable in this rescue scenario, are classified as loose-fitting powered air purifying respirators (PAPR). While they do not require fit testing, they are required to be used in a respiratory protection program under OSHA’s Respiratory Protection Standards, 29 CFR 1910.134. OSHA has established Assigned Protection Factors (APF) for this type of respirator, so a risk assessment would not be required to determine the level of protection afforded in the use of these respirators.

    Why couldn’t the FDNY utilize speech transmitters for their respirators to overcome the communication barrier?
    Most respirators used by municipal fire departments, including by the Fire Department of NYC, are equipped with speech enhancing capabilities, similar to the military masks that you referenced. This can range from mechanical diaphragms to electronic devices to enhance speech capabilities when the respirator is worn. Speech recognition while wearing a respirator is impaired when compared to non-respirator wear, even with the best available speech-enhancing capabilities. That is usually the basis of complaint by respirator wearers about impaired communications.

Comments are closed.

Post a Comment

Page last reviewed: January 30, 2020
Page last updated: January 30, 2020