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Current Air Emissions Exposure of On-Base Personnel



ATSDR completed Phase I of the Kelly Air Force Base (AFB) public health assessment (PHA) inAugust 1999. ATSDR recommended further investigation of potential exposures toenvironmental air contamination from Kelly AFB be performed during Phase II.

This health consultation is a part of Phase II. It reports the results of the evaluation of thepotential exposure of on-base personnel to current air emissions from stationary sources at KellyAFB. These on-base personnel are not covered by the regulations of the Occupational Safety andHealth Association (OSHA). ATSDR concludes that potential exposures of on-base personnel tocurrent air emissions from stationary sources are not likely to result in adverse health effects.This conclusion is based on air dispersion modeling of data from the 1996 Kelly AFB airemissions inventory.


The late Congressman Frank Tejeda petitioned ATSDR to investigate environmentalcontaminant releases from Kelly AFB and the adverse health effects reported by communityresidents in neighborhoods north and southeast of the base. ATSDR publicly released findingsduring Phase I of the public health assessment on August 24 1999, and also described activitiesto be performed during Phase II. During Phase I, ATSDR performed an air dispersion screeningmodel of air emissions from stationary sources to estimate possible air contaminantconcentrations in the community. Results of the air dispersion model indicated the highestestimated contaminant concentrations may be present on base. These emissions may result inexposure to on-base personnel. These personnel may not be protected by OSHA regulations forthe specific emission since their occupational environment is outside the occupationalenvironment generating the specific emission. These potential exposures are consideredenvironmental exposures and not occupational exposures.

The results of the screening model and risk analysis performed during the Phase I evaluationindicated that the estimated increase in the risk for developing cancer may have been highest insome areas on base. ATSDR concluded from the Phase I evaluation that health effects would beunlikely due to current air exposures. ATSDR recommended that a refined air dispersion modelbe performed during Phase II to reduce uncertainty in the initial air dispersion modeling. Currentexposures are defined by ATSDR for purposes of this document as those occurring from 1996 to base closure, which is scheduled to occur during 2001.


ATSDR questioned whether on-base personnel were being exposed to contaminants in ambientair that were emitted by on-base processes (stationary sources) at Kelly AFB. OSHA regulatesthe workplace environment and protects workers from exposure to chemicals to which there isforeseeable exposure. Usually workers are protected from chemicals that they work with andchemicals that are generated during the industrial process. For example, a worker may berequired by OSHA to wear a respirator for protection from solvent fumes. Another worker froma different occupation which does not involve solvents may not be required to wear a respirator.If solvent fumes are emitted from one work environment and enter another work environment,these workers may not be protected from this secondary exposure. It is this secondary exposurethat ATSDR addresses in this consultation.

ATSDR performed an air dispersion model of stationary sources to estimate the concentration ofcontaminants in the ambient air on base. ATSDR used the Environmental Protection Agency'sIndustrial Source Complex Short Term - 3 (ISCST-3) to model the air dispersion of the 1996 airemissions inventory from Kelly AFB. ATSDR estimated what happened to air emissions fromindustrial processes on base when they were released into ambient air. A computer model estimated the effect meteorological parameters such as air speed, wind direction, and temperaturemay have had on the contaminant. The computer model estimated the concentration of thecontaminant as it spread out from its source of emission.

In performing this evaluation, ATSDR used an approach which considers all of the health andenvironmental evidence to evaluate potential health effects [2]. The estimated contaminantconcentrations were compared to exposure levels that would not be expected to result in adversehealth effects (i.e., comparison values). Those contaminants exceeding their screening values arefurther evaluated. Acute (short term) and chronic (long term) exposures are further evaluated bycomparing levels of exposure to levels associated with noncancer health effects reported in thescientific literature. Chronic exposures are also evaluated for potential cancer health effects byperforming a risk assessment using site specific exposure scenarios rather than the generalassumptions used to develop screening values.

Short term exposures

Short term (acute) exposures to estimated levels of contaminants in ambient air, other thanformaldehyde, are unlikely to result in adverse health effects. Laboratory and occupationalhuman exposure studies have been conducted with both normal and asthmatic individuals todetermine potential effects from formaldehyde exposure [3-6]. The maximum 1- hourformaldehyde concentration over a 5-year period is estimated to be 1223 mg/m3, which is near thelowest levels that have been associated with acute eye, nose, or upper respiratory irritation [7].Most individuals cannot tolerate above 6000 mg/m3 and symptoms may become severe above12,000 - 24,000 mg/m3[8]. Based on the results of air modeling and estimated exposure, it may bepossible for individuals who are sensitive to formaldehyde and are within 300 meters downwindof the jet engine testing facility (see Figure 2) during the 1-hour maximum concentrationemission to experience mild to moderate eye irritation. It is estimated that these conditions couldoccur on the average of once per week.

Long term exposures

Potential long term (chronic) exposures for noncancer health effects would be unlikely becauseall estimated contaminant levels are below screening values for long term noncancer healtheffects.

ATSDR also evaluated potential long term exposures for cancer health effects. The results ofscreening and subsequent risk assessment are presented in Table 1. The contaminants listed(hexavalent chromium, hydrazine, arsenic, formaldehyde, 1,3-butadiene, benzene, acetaldehyde,tetrachloroethylene or PCE, and cadmium) are those that exceeded the screening values. A riskassessment was then performed to estimate the increase in the risk for developing cancer fromchronic exposure to the contaminant. Results of the risk assessment indicates that there is noapparent increase (see Table 2) in risk for developing cancer from the estimated exposure level.

ATSDR evaluated whether health effects might be likely from simultaneous exposure to anumber of chemicals. ATSDR calculated an estimated risk from potential exposure to each of thechemicals (see Table 1) and added the risk to all of the chemicals at points over the base. Thisinformation shows the estimated level of risk for developing any type of cancer from exposure toall of the chemicals (cumulative risk), and the location of the estimated cumulative risk (seeFigure 1). The maximum cumulative risk estimated from exposure anywhere on base is8/100,000 (or 1 case of any cancer for every 12,500 workers exposed). Based on this level ofexposure, there would be no apparent increase in risk (see Table 2). ATSDR concludes that anincrease in the number of individuals developing cancer from current on-base exposures to airemissions from Kelly AFB would not be observed in the population of on-base personnel.

The individual contaminant contributing the greatest amount of risk was hexavalent chromiumwith an estimated increase in risk of 6/100,000. It is unlikely that adverse health effects would beobserved in this population from this level of exposure. The level of hydrazine is over reported,but included because the actual level of relevant emission was not available. While the Air Forceuses diesel fuel instead of hydrazine in planes constructed in recent years, the exact number ofeach type plane on base at any time can vary. ATSDR assumed a worst-case scenario andincluded all hydrazine as ground level fugitive emissions. The estimated risk at this level is2/100,000, and it is unlikely that adverse health effects would be observed in this population. Theother contaminants (arsenic, formaldehyde, 1,3-butadiene, benzene, acetaldehyde, PCE, andcadmium) did not contribute significantly to the overall increase in risk.

The locations of the maximum concentrations of the individual contaminants of greatest concernare depicted in Figure 2. The associated increases in risk are reported in Table 1. Air dispersionof each contaminant was simulated at 5100 points in and around Kelly AFB with the points 300meters apart, covering an area of approximately 117 square miles. The points identified in Figure2 represent emissions that were located within a 300 meter radius of the point. Contaminantemissions of concern are primarily located in two areas where painting, plating, and degreasingor jet engine repair is performed.

Exposure conditions used in the risk assessment were an individual with a 70 kilogram (kg) bodyweight, exposed for a frequency of 8 hours/day, 5 days/week, 50 weeks/year for a duration of 7years. Seven years was used for current exposures because of the projected base closing in 2001(1996-2002 inclusive).

Many Air Force industrial operations have already been reduced or eliminated at Kelly AFB andATSDR believes that using the 1996 emissions inventory is an appropriate conservative worse-case scenario for current emissions. Past emissions (prior to 1996) are currently beinginvestigated and will be reported when complete. ATSDR cannot predict future emissions frompotential future tenants. These future emissions can be addressed with the Texas NaturalResource and Conservation Committee (TNRCC).


Environmental exposures to estimated current air emissions from stationary sources at Kelly AFB would not be expected to result in adverse health effects to on-base personnel.


  1. ATSDR. 1999. Public Health Assessment for Kelly Air Force Base. Phase I. PublicComment. U.S. Department of Health and Human Services. August 20, 1999.

  2. Weis BK and Susten AS. Groundwater Contamination by PCE and TCE: ATSDR'sApproach to Evaluating Public Health Hazard. Unpublished manuscript.

  3. Harving H, Korsgaard J, Pederson OF, Molhave L, Dahl R. 1990. Pulmonary function andbronchial reactivity in asthmatics during low-level formaldehyde exposure. Lung 168:15-21.

  4. Kulle JT, Sauder LR, Hebel JR, Green D, Chatham MD. 1987. Formaldehyde dose-responsein health nonsmokers. J Air Pollution Control Assoc 37:919-924.

  5. Sheppard D, Eschenbacher W, Epstein J. 1984. Lack of bronchomotor response to up to 3ppm formaldehyde in subjects with asthma. Environ Res 35:133-139.

  6. Schachter NE, Witek TJ Jr, Brody DJ, Tosun T Beck GJ, Leaderer BP. 1987. A study ofrespiratory effects from exposure to 2.0 ppm formaldehyde in occupationally exposedworkers. Environ Res 44:188-205.

  7. Wever-Tschopp A, Fisher T, Granjean E. 1997. Irritating effects of formaldehyde on men. Int Occup Environ Health. 39:207-218.

  8. Feinman SE, editor. 1988. Formaldehyde sensitivity and toxicity. Boca Raton (FL):CRCPress Inc.


David A. Fowler, PhD
Petitions Response Section
Exposure Investigations and Consultations Branch
Division of Health Assessments and Consultations

Brian Kaplan, MS
Consultations Section
Exposure Investigations and Consultations Branch
Division of Health Assessments and Consultations

Morris Maslia, PE
Exposure Investigations Section
Exposure Investigations and Consultations Branch
Division of Health Assessments and Consultations

Reviewed by:

John E. Abraham, PhD
Branch Chief
Exposure Investigations and Consultations Branch
Division of Health Assessments and Consultations

Susan Moore
Section Chief, Consultations
Exposure Investigations and Consultations Branch
Division of Health Assessments and Consultations


Table 1.

Contaminants Exceeding Screening Values
Contaminant Maximum Annual Average Concentrationa Screening Valueb Estimated Riskc
Hexavalent Chromium 0.034 0.00008 6/100,000
Hydrazine 0.159d 0.00039e 2/100,000
Arsenic 0.024 0.0002 2/1,000,000
Formaldehyde 7. 0.08 2/1,000,000
1,3-Butadiene 0.84 0.004 5/1,000,000
Benzene 0.91 0.1 2/10,000,000
Acetaldehyde 2.2 0.5 1/10,000,000
PCE 8.36 3.3e 1/10,000,000
Cadmium 0.0024 0.0006 9/100,000,000

Table 1 is a comparison of the maximum concentrations of estimated air emissions with chronicscreening values which are considered by ATSDR to be levels at which adverse health effectswould not be expected. Maximum concentrations which exceeded screening values are furtherevaluated by risk assessment to estimate the relative degree of hazard.

  1. All units are in µg/m3 (micrograms per cubic meter). Average annual concentration is the maximum concentration estimated at any location on base. Concentrations from 1996 air emissions inventory modeled with EPA's Industrial Source Concentration Short Term 3 (ISCST3) air dispersion model.

  2. Screening Values are ATSDR's Cancer Risk Evaluation Guide (except were indicated) which assumes a daily exposure for a lifetime (70 years).

  3. Estimated risk calculated using Environmental Protection Agency (EPA) Region 6 Inhalation Slope Factors, assuming a body weight of 70 kilograms (kg), for an exposure of 8 hours/day, 5 days/week, 50 weeks/year for 7 years.

  4. Hydrazine concentration is over-reported, see text.

  5. EPA Region 6 Human Health Medium-Specific Screening Level for ambient air were used where an ATSDR screening value was not available.

Table 2.

Category Definitions
Category Fraction Decimal Exponential
No Increased Risk <1/100,000 <0.00001 <1E-05
No Apparent Increased Risk 1/100,000 0.00001 1E-05
Low Increased Risk 1/10,000 0.0001 1E-04
Moderate Increased Risk 1/1,000 0.001 1E-03
High Increased Risk 1/100 0.01 1E-02
Very High Increased Risk >1/100 >0.01 >1E-02

Table 2. Category definitions used by ATSDR are intended to define categories of estimated riskto convey the degree of hazard from the defined exposure relative to other exposures. Categoriesare derived from ATSDR Decision Statement TOX.14. Draft QAA-27. Revised October 21,1991.


Estimated Curative Cancer Risk from Current Air Dispertion Modeling
Figure 1. Estimated Curative Cancer Risk from Current Air Dispertion Modeling

Current Air Dispertion Modeling - Estimated Cumulative Cancer Risk and Maximum Air Concentrations
Figure 2. Current Air Dispertion Modeling - Estimated Cumulative Cancer Risk and Maximum Air Concentrations

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