Occupational exposures to air contaminants at the World Trade Center disaster site--New York, September-October, 2001.

Amid concerns about the fires and suspected presence of toxic materials in the rubble pile following the collapse of the World Trade Center (WTC) buildings on September 11, 2001, the New York City Department of Health (NYCDOH) asked CDC for assistance in evaluating occupational exposures at the site. CDC's National Institute for Occupational Safety and Health (NIOSH) collected general area (GA) and personal breathing zone (PBZ) air samples for numerous potential air contaminants. This report summarizes the results of the assessment, which indicate that most exposures, including asbestos, did not exceed NIOSH recommended exposure limits (RELs) or Occupational Safety and Health Administration (OSHA) permissible exposure limits (PELs). One torch cutter was overexposed to cadmium; another worker was overexposed to carbon monoxide (CO) while cutting metal beams with an oxyacetylene torch or a gasoline-powered saw, and two more were possibly overexposed to CO. NIOSH recommended that workers ensure adequate on-site ventilation when using gas-powered equipment and use rechargeable, battery-powered equipment when possible.

AMID CONCERNS ABOUT THE FIRES AND suspected presence of toxic materials in the rubble pile following the collapse of the World Trade Center (WTC) buildings on September 11, 2001, the New York City Department of Health (NYCDOH) asked CDC for assistance in evaluating occupational exposures at the site. CDC's National Institute for Occupational Safety and Health (NIOSH) collected general area (GA) and personal breathing zone (PBZ) air samples for numerous potential air contaminants. This report summarizes the results of the assessment, which indicate that most exposures, including asbestos, did not exceed NIOSH recommended exposure limits (RELs) or Occupational Safety and Health Administration (OSHA) permissible exposure limits (PELs). 1,2 One torch cutter was overexposed to cadmium; another worker was overexposed to carbon monoxide (CO) while cutting metal beams with an oxyacetylene torch or a gasolinepowered saw, and two more were possibly overexposed to CO. NIOSH recommended that workers ensure adequate on-site ventilation when using gas-powered equipment and use rechargeable, battery-powered equipment when possible.
Toxic substances of concern included asbestos (from insulation and fireproofing materials), concrete (made from Portland cement and used in the buildings' construction) and the crystalline silica it contained, CO (from fires and engine exhaust), diesel exhaust (from vehicles and equipment), mercury (from fluorescent lights), chlorodifluoromethane (Freon™-22, from air conditioning systems), heavy metals (from building materials), hydrogen sulfide (from sewers, anaerobically decomposing bodies, and spoiled food), inorganic acids, volatile organic compounds (VOCs), and polynuclear aromatic hydrocarbons (PAHs) (from fires and engine exhaust). Environmental sampling during September 18-October 4 focused on searchand-rescue personnel, heavy equipment operators, and workers cutting metal beams but also included various other occupations. A total of 1,174 air samples was collected, including 804 for asbestos. NYCDOH contractors collected most of the asbestos samples; NIOSH personnel collected all other samples. In addition, NIOSH collected 33 bulk samples of dust, debris, and other materials. All samples were collected and analyzed according to the NIOSH Manual of Analytic Methods 3 with some modifications.
A total of 29 bulk samples of undisturbed settled material from various locations was analyzed for asbestos; 27 of these also were analyzed for crystalline silica and metals. Of the 29 samples, 26 (90%) had Ͻ1% asbestos (by mass); the three others had 1%-3%. All but one of 27 samples had crystalline silica; concentrations (by mass) ranged from 0-18%, with a median (for all 27 samples) of 3.2%. The most abundant metals in the samples were calcium, magnesium, aluminum, iron, and zinc. Lead, arsenic, cadmium, and beryllium concentrations (by mass) were Ͻ0.1%. Three bulk samples of fireproofing material on I-beams from the main debris pile were analyzed for asbestos; one was negative, and two had Ͻ1% asbestos. A sample of paint from a metal beam had 0.3% lead.
Phase contrast microscopy (PCM) revealed fibers in 358 (45%) of the 804 asbestos air samples. Excluding 30minute samples, 25 samples had fiber concentrations that, if the fibers had been asbestos, would have exceeded the REL of 0.1 fibers per cubic centimeter of air (f/cc). 1 None of the 30-minute sample concentrations exceeded the OSHA short-term excursion limit of 1.0 f/cc. 2 Of the 25 samples with fiber concentrations 0.1 f/cc (range: 0.1-0.5 f/cc) by PCM, 18 were analyzed by transmission electron microscopy (TEM), which can distinguish between asbestos and nonasbestos fibers. All had asbestos concentrations Ͻ0.1 f/cc. The seven samples not analyzed by TEM had fiber concentrations ranging from 0.1-0.2 f/cc. Differential analysis by polarized light microscopy of these same 25 air samples revealed most nonasbestos fibers to be fibrous glass, gypsum, and cellulose.
Air concentrations of total (36 samples) and respirable (18 samples) particulate ranged up to 2.3 milligrams per cubic meter (mg/m 3 ) and 0.3 mg/ m 3 , respectively, which are below the corresponding RELs of 10.0 mg/m 3 and 5.0 mg/m 3 for Portland cement. 1 1 One was from a torch cutter and the other from a gasoline-powered saw operator. In 99 air samples, concentrations of CO ranged from 0.2 to 242.0 ppm; the highest finding (in a 32 1 ⁄2-minute PBZ sample from a saw operator) exceeded the NIOSH limit of 200 ppm and would have exceeded the PEL of 50 ppm (8hour TWA) had it been sustained for 2 hours. 1,2 CO concentrations of 41 ppm and 45 ppm in PBZ samples from torch cutters and 40 ppm in a GA sample near a saw operator, with sampling durations of 1 ⁄2, 5, and 2 1 ⁄2 hours, respectively, would have exceeded the REL of 35 ppm had they represented fullshift exposures. 1,2 Hydrogen sulfide was present in seven of 10 samples, one or more inorganic acids in all 27 samples, mercury in five of 16 samples, and one or more VOCs in 14 of 76 samples; all concentrations were below applicable NIOSH and OSHA exposure limits except for two benzene concentrations (0.4 mg/m 3 and 0.5 mg/m 3 ) that exceeded the REL of 0.3 mg/m 3 . 1 Both were in GA samples from a smoke plume and did not represent any specific worker's exposure. The highest concentration of elemental carbon (an indicator of diesel exhaust) was 0.023 mg/m 3 . Neither NIOSH nor OSHA has a numerical exposure limit for diesel exhaust, but the American Conference of Governmental Hygienists has proposed a limit of 0.2 mg/m 3 (measured as elemental carbon). 4 No Freon™-22 was detected in any of five samples. Small amounts of various PAHs were present in all 12 samples, but not at concentrations that exceeded individually or collectively any applicable NIOSH or OSHA exposure limit.

CDC Editorial Note:
In addition to the physical hazards associated with work at the WTC site, hazardous exposures to toxic dusts and gases were suspected initially. Asbestos exposure, in particular, was an occupational and community health concern. The findings of this survey documented no occupational exposure to asbestos, at least after September 18, in excess of NIOSH or OSHA occupational exposure limits. The seven air samples that had fiber concentrations (determined by PCM) higher than the REL for asbestos probably would have had asbestos concentrations Ͻ0.1 f/cc if analyzed by TEM. In many other samples, asbestos concentrations determined by TEM tended to be lower than those determined by PCM. The NIOSH asbestos sampling did not provide data about occupational exposures before September 18 and was designed to assess occupational exposures, not community exposures, which probably were lower.
The absence of exposure to respirable crystalline silica, despite its presence in the bulk samples, indicates either that the crystalline silica in the dust at the site consisted of larger, nonrespirable particles or that work activities were not causing the dust to become airborne. In the absence of effective dust-control measures, the former explanation seems more likely. Although the air sampling indicated the presence of respirable airborne particulate, this material was apparently not crystalline silica. One torch cutter had cadmium overexposure, and excess CO was associated with workers using oxyacetylene torches and gasolinepowered saws. To reduce CO exposure, NIOSH recommended replacing gasoline-powered saws with rechargeable, battery-powered saws.
At the time of the NIOSH sampling, the ambient air did not appear to be contaminated with toxic substances from the buildings or their contents or with combustion products to an extent that posed an occupational health hazard. However, the presence of hazards related to specific work activities at the WTC disaster site underscores the importance of assessing suspected occupational exposures. In response to the WTC disaster, NIOSH has issued guide-lines for addressing a variety of occupational safety and health hazards at disaster sites. 5

Acknowledgments
This report is based on data contributed by: New York City School Construction Authority. Data Chem Laboratories, Salt Lake City, Utah.   animal before capture. These five persons were interviewed by county health department personnel, who reported that although the beaver had made aggressive actions, the animal had not bitten anyone. This report summarizes the investigation of this case of animal rabies. Mammals that exhibit aggressive or other unusual behavior should be reported promptly to local health officials and should not be approached or handled by the public.
On November 27, the FDoH laboratory diagnosed rabies in the brain tissue of the beaver by using a fluorescent antibody test. Monoclonal antibody strain typing indicated that the virus belonged to the antigenically distinct group of viruses found in raccoons in the eastern United States. Park personnel involved in the capture of the animal received postexposure prophylaxis. No treatment was recommended for the five persons who had been in the vicinity.
Of 3,751 animal specimens submitted for rabies testing to the FDoH during 2001, a total of 198 (5.3%) tested positive for rabies. In addition to the beaver, specimens included 124 raccoons, 34 foxes, 19 bats, 15 cats, two otters, one dog, one bobcat, and one horse. In 2001, no other rabid animals were identified in Alachua County. However, seven raccoons, four bats, three foxes, and one dog were reported with rabies in neighboring counties.

CDC Editorial Note:
This report describes the first finding of rabies in a beaver in Florida. Although rodents are not a wildlife reservoir for rabies virus and no rabies transmission from rodents to humans has been documented, reported cases of rabies in rodents have been increasing in the United States, from 97 cases during 1971-1984 1 to an average of 52 cases per year during 1995-2000. [2][3][4][5][6][7] This trend is attributed to an increase in cases among large rodents (e.g., woodchucks [Marmota monax] and beavers [Castor canadensis]), with most cases occurring in the eastern states, where a raccoon rabies epizootic has been documented. 3,8 Reported rabies in Florida rodents is uncommon. Woodchucks are not native to Florida, and the natural range of the beaver is restricted to the northern portion of the state. Large rodents share habitats with terrestrial carnivore rabies reservoirs (e.g., raccoons, skunks, and foxes) and because of their size have a greater chance of surviving an encounter with a rabid carnivore. In these areas, rabies should be considered in the differential diagnosis of any mammal with unexplained neurologic illness. Possible human and pet exposures to rabies should be evaluated by public health officials on an individual basis. Bites from small rodents that are unlikely to survive an encounter with a rabid animal rarely require rabies postexposure prophylaxis; however, bites from large rodents should be considered as possible rabies exposures, especially in areas where rabies is endemic. 9 Persons should avoid any mammal exhibiting aggressive or unusual behavior. Persons who suspect that they have been exposed to a rabid animal should contact a healthcare provider immediately. NLVs can be transmitted by fecally contaminated food and water 1 and by direct person-to-person contact or through droplets of infected persons. Outbreaks of NLV-associated gastrointestinal illness are common in military settings. During May 13-19, 2002, a total of 29 British soldiers and staff of a field hospital in Afghanistan became acutely ill after a short incubation period with vomiting, diarrhea, and fever. This report summarizes the investigation of this outbreak and underscores the importance of the diagnostic capacity for NLVs.

Outbreak of Acute
The first three patients presented with severe acute illness characterized by headache, neck stiffness, photophobia, obtundation, and gastrointestinal symptoms, which made the initial diagnosis elusive. The third patient's illness was complicated by disseminated intravascular coagulation. Two of these patients required ventilatory support in the field hospital's intensive care unit. All bacteriologic studies performed at the field hospital's laboratory were negative. Because the cause of the illness was unknown, the field hospital was closed to all but patients with gastrointestinal symptoms. Because of the field conditions at the base and the severity of illness in the initial patients, one patient was evacuated to a U.S. military hospital in Germany, and 10 were evacuated to England. Two medical staff who treated the patients on the flight to England and a third contact at the hospital in England subsequently developed gastroenteritis; two of these persons were hospitalized for several days. All patients recovered rapidly and were discharged. The field hospital has since reopened with enhanced infection-control precautions.
In England, fecal specimens were tested for NLVs by electron microscopy (EM), a new antigen-capture enzyme-linked immunosorbent assay (ELISA), and reverse transcriptionpolymerase chain reaction (RT-PCR). By EM, clumps of small, roundstructured viruses were observed and considered to be consistent with NLVs. This finding was confirmed by ELISA and RT-PCR in specimens from five patients. Partial sequence analysis of the polymerase gene identified the virus as belonging to genogroup II, 2

CDC Editorial Note:
Outbreaks of NLV-associated gastrointestinal illness are common, particularly in military deployments. NLVs were the most common cause of disability among soldiers in Operations Desert Storm and Desert Shield, have caused outbreaks aboard aircraft carriers, 4 and have been a common problem in the Israeli military. 5 NLVs are extremely contagious because of their low infectious dose (Ͻ100 viral particles), prolonged asymptomatic shedding (up to 2 weeks after recovery), ability to resist chlori-nation (10 ppm chlorine), and stability in the environment (stable with freezing and at 140°F [60°C]). Secondary cases and nosocomial spread are common, 3 although the risk for NLV infection in the health-care setting can be minimized through the use of appropriate infection-control practices. 6,7 NLV gastroenteritis has several distinguishing characteristics, including diarrhea, vomiting, a short duration of illness (1-3 days), and a short incubation period (24-48 hours). The illness is generally mild, but it can cause severe disease with associated dehydration and electrolyte imbalance that might require hospitalization and aggressive treatment with intravenous fluids. Severe illness with NLVs has been associated with group O blood phenotype. 8 The diagnosis of NLVs from stool specimens is difficult and depends on the identification of the viral RNA by RT-PCR, direct visualization of the viral particles by EM, and/or evidence of a specific antibody response in acuteand convalescent-phase serum specimens. 3 Further characterization of the NLV into genogroups is possible by sequence analysis at reference laboratories. In the United States, detection by PCR is limited to some state health department and reference laboratories. Health-care providers generally consider the diagnosis on clinical grounds without seeking laboratory confirmation. As a result, many more outbreaks probably occur, but attribution to NLVs has been infrequent because of the difficulty of diagnosis. Simpler, less time-and labor-intensive diagnostic methods are under development. New antigen-capture assays, such as the ELISA used in this outbreak investigation, are being tested in Japan and Europe but have not yet been evaluated fully in the United States.
In this outbreak, the inability to identify an etiologic agent promptly and the unusual severity and atypical presentation of disease in the initial cases resulted in the illness being termed a "mystery infection." This uncertainty led to the air evacuation of ill soldiers, during which secondary spread of the infection to health-care providers aboard one of the military flights occurred. The diagnosis was ultimately made in England, where EM and the new ELISA identified the etiologic agent as an NLV. Confirmation and characterization of the virus as a genogroup II strain was obtained by PCR and sequence analysis. Field laboratory capacity for NLV diagnosis might have given on-site health-care providers information useful for limiting secondary spread of illness more effectively and allayed the fear and anxiety associated with the label of "mystery infection." The same observation can be made for most acute gastroenteritis outbreaks in the United States that elude an etiologic diagnosis.
This outbreak demonstrates that NLV-associated illness occurs commonly and needs to be identified promptly so that patterns of transmission can be identified and interrupted. The development of simple and sensitive detection techniques remains a high priority. When these become available, the true burden of illness can be measured and more effective control measures implemented.