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A refuse dump near Naco, Sonora, Mexico, caught fire and burned from December 1 to December 5,2001. The fire, which consumed large quantities of household refuse, also generated a large quantityof smoke. During this period, considerable smoke was intermittently present in Naco, Arizona. Personsup to 17 miles away from the fire reported smelling the smoke. At night in the Naco area, smokeconcentrations were generally higher when weather conditions caused smoke to settle in residentialneighborhoods on both sides of the border.

The Arizona Department of Health Services and the Cochise County Health Department issued publichealth advisories for the evenings of December 1 and 2, 2001. The Naco, Arizona, Port of Entry closedduring periods of heavy smoke to protect the health and safety of employees and travelers. The CochiseCounty Board of Supervisors declared a state of emergency to gain access to state and federal resources.

This report summarizes the events that occurred during the fire and analyzes the data collected by theArizona Department of Health Services and the Arizona Department of Environmental Quality todetermine the extent of the public health threat from the fire.


Saturday, December 1, 2001
The Cochise County Health Department received calls from citizens complaining about the smoke. The Arizona Department of Environmental Quality Hazardous Air Response Team (HART) arrived in Naco on the U.S. side in the late afternoon to monitor the air downwind of the dump fire.

The HART team reported the location of the dump fire as approximately 1.5 miles east of the U.S.Customs station on the Mexican side of the U.S.-Mexico border. At 6:45 p.m., initial instantaneousreadings of particulate matter smaller than 10 microns (PM-10) were approximately 350 microgramsper cubic meter (ug/m3).

As a result of the levels of respirable particulate matter (PM-10) measured and the expectation that therewould be higher particulate levels during the evening, the Cochise County Health Department and theArizona Department of Health Services issued a health advisory for the Naco, Arizona, area forDecember 1. The news release recommended that persons remain indoors during the night and shut theirwindows, that persons with respiratory problems in the Naco area see their physicians if they haverespiratory symptoms, and that those with respiratory problems should consider finding an alternativeplace to sleep. The advisory notices were distributed by the Cochise County Sheriff's Office.

Sunday, December 2, 2001
PM-10 readings on the morning of December 2 ranged from 250 ug/m3 to 1,901 ug/m3. Air sampling results for hydrochloric acid and carbon monoxide were below the minimum detectable limit.

PM-10 levels decreased throughout the early morning as winds picked up. By 5:30 a.m., the PM-10concentration was down to 221 ug/m3. The HART team continued to monitor and record the PM-10concentrations throughout the day. The readings steadily declined as the heating of the day dispersed thesmoke. Hourly averages in Naco, Arizona, dropped to as low as 5.8 ug/m3 in the early afternoon.

The Cochise County Health Department and the Arizona Department of Health Services continuedthe health advisory for the evening of December 2 in anticipation of calm weather conditions.

Monday, December 3, 2001
A storm began to move into the area in the early afternoon of December 3. Winds from the west picked up and kept the plume blowing away from Naco, Arizona. Rain began to fall in the early afternoon and continued until about midnight. The winds associated with the weather system prevented the smoke from settling in Naco on the evening of December 3. In addition to the wind and precipitation, firefighting efforts at the dump kept the smoke from impacting Naco, Arizona.

December 4 and 5, 2001
The ADEQ sampling team continued to monitor throughout the night and into December 5, 2001. PM-10 levels generally remained well below 50 ug/m3 except for one hourly average of 60 ug/m3. The ADEQ team concluded that the fire was nearly contained on December 5. The team continued monitoring air quality during the evening hours of December 5, 2001, and early morning hours of December 6, 2001. The fire was officially out on December 6, 2001.


This public health evaluation was prepared using PM-10 air sampling data collected by the ADEQ andobservations made by ADHS staff during the event.

This report evaluates environmental sampling data by comparing the PM-10 analytical results toestablished screening levels and data in the scientific literature to determine the magnitude of the publichealth threat from the fire. The primary screening values used to evaluate the particulate matter are theU.S. Environmental Protection Agency Ambient Air Quality Standards and Emergency Episode Levelsand the World Health Organization Health Guidelines for Vegetation Fire Episodes.1


The ADEQ HART team arrived at the scene on December 1 at approximately 6 p.m. The team set upa portable PM-10 monitor at the U.S. Customs station in Naco, Arizona, to quantify respirableparticulate matter (PM-10) levels throughout the fire event. Sampling for particles was conducted usingthe HART team tapered element oscillating microbalance (TEOM). The TEOM is calibrated inaccordance with operational requirements by the HART sampling team.

The following tables summarize the PM-10 data collected by the sampling team during the event. Table1 displays the 1-hour averages measured during the fire. Table 2 displays the 24-hour average concentrations.

Table 1.

Naco Dump Fire 1-Hour Average PM-10 Levels
  1-Hour Average PM-10 Range (ug/m3 ) 1-Hour WHO Alert Stage Guideline (ug/m3 ) Exceeds the WHO 1-Hour PM-10 Alert Stage?
December 1, 2001      
Overnight 210-524 400 Yes
December 2, 2001      
Daytime 7-129 400 No
Overnight 211-590 400 Yes
December 3, 2001      
Daytime 17-72 400 No
Overnight 4-79 400 No
December 4, 2001      
Daytime 30-60 400 No
Overnight 2-18 400 No
December 5, 2001      
Daytime 4-39 400 No
Overnight 10-59 400 No

Table 2.

Naco Dump Fire 24-Hour Average PM-10 Levels
  24-Hour Average PM-10 Concentration (ug/m3 ) 24-Hour EPA Standard (ug/m3 ) Exceeds the EPA 24-Hour PM-10 Standard?
December 1, 2001* 333 150 Yes
December 2, 2001 198 150 Yes
December 3, 2001 110 150 No
December 4, 2001 99 150 No
December 5, 2001 23 150 No

* 7 p.m. to 12 p.m. average


The major emissions from burning refuse are particulate matter containing a variety of combustionproducts. The particles in the smoke are too small to be filtered by the nose and upper respiratorysystem, so they wind up deep in the lungs. They can remain there for days, potentially causing tissuedamage and respiratory health effects.

The likelihood of exposure to smoke causing a decrease in lung function is well recognized. Theoccurrence of respiratory illness in children has been shown to increase as concentrations of particulatematter rise. Symptoms include lower respiratory infections and bronchitis. Smoke also aggravatesasthma, emphysema, and bronchitis. It can also irritate the eyes and can trigger headaches and allergies.

Epidemiological studies have consistently found that prolonged exposure to PM-10 might result inshortness of breath, increases in coughs, aggravation of asthma, decreases in lung function and lungdefense mechanisms, chronic obstructive pulmonary disease, and increased rates of hospitalization forrespiratory and cardiovascular illnesses.2-13

During the fire, smoke from burning refuse was intermittently present in the residential neighborhoodsin the Naco area on both sides of the border. The concentrations of PM-10 sometimes changed byseveral hundred ug/m3 in minutes. 1-hour average measurements of PM-10 in Naco on the evenings ofDecember 1 and 2 ranged from 210 ug/m3 to 590 ug/m3. Readings in the 200 to 300 ug/m3 range werecommon at night when winds were calm. People in the neighborhoods were generally in their homesduring this time.

Particulate matter gets into the indoor air of homes even when doors and windows are shut. Thecontribution made by PM-10 on indoor air from the outside depends on how airtight the house is andthe average outdoor PM-10 concentration. Particle size can also affect how quickly outdoor particulatematter gets into homes since larger particles will stick to surfaces more readily than smaller particles.Since average PM-10 concentrations are not known, and because of the variability in how airtighthomes are depending on their structure and operation, it is not possible to determine what theconcentrations of particulate matter might have been in area homes during the fire.

The outdoor PM-10 concentrations at night on December 1 and 2, 2001, were sufficient to result in atransient decrease in lung function. Plausible symptoms in area residents include cough, other lowerrespiratory symptoms, and possibly aggravated asthma symptoms.

During the fire, the concentration of PM-10 was generally lower during the daytime. However, humanactivity and outdoor exposure are higher during the day. These factors increase exposure and thepotential for health effects. Health problems might have included a transient decrease in lung function.Other potential symptoms in area residents might have included cough, other lower respiratory symptoms, and possibly aggravated asthma symptoms.


ADHS staff contacted local schools and the Naco School District to communicate health risks, providesafety advice, and assess the public health impact of the fire. School personnel reported complaints ofhaze and odor, and some children with asthma were reportedly sent home.

Eight firefighters were treated and released for smoke inhalation at the main hospital in Naco, Sonora,Mexico. In addition, physicians at the main hospital in Naco, Sonora, reported seeing several of theirpatients who have had previous and recurring respiratory problems. Physicians in Naco, Arizona, alsoreported seeing patients with respiratory symptoms that might have been aggravated by the smoke. Staffat the U.S. Port of Entry in Naco, Arizona, reported seeing several people on both sides of the border going to the other side for medical treatment.


ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and childrendemand special emphasis in communities faced with contaminants in air. Children are more likely tobe exposed because they play outdoors. Their developing body systems can sustain permanent damageif toxic exposures occur during critical growth stages.

Furthermore, children, even those without pre-existing illness or chronic conditions, are susceptible toair pollution because their lungs are still developing, and they are often engaged in vigorous outdooractivities, making them more sensitive to pollution than healthy adults. Studies have shown that inchildren, particulate pollution is associated with increased episodes of coughing and difficulty breathing,and decreased lung function. Children, particularly those with asthma, likely were among the most affected persons during the refuse fire.


ADHS finds that the smoke likely caused an increase in respiratory problems in some Naco, Arizona,and Naco, Sonora, residents on December 1 and 2, 2001. The symptoms would be expected to beconsistent with smoke inhalation, suggesting that the fire represented an acute (short-term) public health hazard.


No further recommendations are indicated at this time.


Arizona Department of Health Services, Office of Environmental Health

Will Humble, Chief, Office of Environmental Health, Principal Investigator

ATSDR Regional Representative

William Nelson
Office of Regional Operations, Region IX
Office of the Assistant Administrator

ATSDR Technical Project Officer

Gail Godfrey
Division of Health Assessment and Consultation
Superfund Site Assessment Branch
State Programs Section


  1. Johnson RA, and Phonboon K.1998. Guidance on measures for vegetation fire episodic events. Application of appropriate short-term air quality guidelines. World Health Organization. p. 485 - 491.

  2. Pope CA. 1991. Respiratory hospital admissions associated with PM10 pollution in Utah, SaltLake and Cache valleys. Arch Environ Health 46:90-7.

  3. Pope CA, Dockery D. 1992. Acute health effects of PM10 pollution on symptomatic andasymptomatic children. Am Rev Respir Dis 145:1123-8.

  4. Schwartz J, Slater D, et al. 1993. Particulate air pollution and hospital emergency room visitsfor asthma in Seattle. Am Rev Respir Dis147:826-31.

  5. Dockery D, Pope C. 1994. Acute respiratory effects of particulate air pollution. Annu RevPublic Health 15:107-32.

  6. Dockery D, Pope A, et al. 1993. An association between air pollution and mortality in six U.S.cities. N Engl J Med 329(24):1753-9.

  7. Pope CA, Schwartz J. 1992. Daily mortality and PM10 pollution in Utah Valley. Arch EnvironHealth 47:211-17.

  8. Schwartz J, Dockery D. 1992. Increased mortality in Philadelphia associated with daily airpollution concentrations. Am Rev RespirDis 145:600-4.

  9. Schwartz J, Dockery D. 1992. Particulate air pollution and daily mortality in Steubenville,Ohio. Am J Epidemiol 135:12-23.

  10. Pope CA, Thun M. 1995. Particulate air pollution as a predictor of mortality in a prospectivestudy of U.S. adults. Am J RespirCrit Care Med 151:669-74.

  11. Arizona Department of Environmental Quality. Arizona comparative environmental risk project,human health technical committee final report. Phoenix: Arizona Department of Environmental Quality;1995:107-15.

  12. Arizona Department of Environmental Quality. 1991 air quality control for Arizona.Phoenix: Arizona Department of Environmental Quality; 1992 Nov.

  13. Dockery D. 1981. Indoor-outdoor relationships of respirable sulfates and particulates. Atmos Environ15:335-43.


This health consultation was prepared by the Arizona Department of Health Services undercooperative agreement with the Agency for Toxic Substances and Disease Registry. It is inaccordance with approved methodology and procedures existing at the time the health consultation was initiated.

Gail D. Godfrey
Technical Project Officer

The Division of Health Assessment and Consultation (DHAC), ATSDR, has reviewed this health consultation and concurs with its findings.

Sven E. Rodenbeck
for Richard Gillig


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