Epidemiologic Notes and Reports Sulfur Dioxide Exposure in Portland Cement Plants

Complaints of burning eyes, sore throat, and chest tightness by workers in two Portland cement plants led to requests for Health Hazard Evaluations (HHE) conducted by the National Institute for Occupational Safety and Health (NIOSH). The nature of the symptoms, the combustion processes involved, and measurable levels of sulfur dioxide (SO((2))) suggested possible exposure to SO((2)) as the cause of the problems at each plant.

The production of Portland cement begins by crushing and milling sources of calcium, aluminum, and silica, which are then fused in rotary kilns at 1,450 C (2,642 F) and ground into cement powder. The raw materials are fed into the upper end of long, slightly inclined, cylindrical kilns, and fuel is blown into the lower end. Exhaust gases and fugitive dust emissions leave the kilns at the upper end and pass through dust-collection mechanisms called baghouses. These consist of a series of filters in the form of long cloth tubes or bags that collect particulate matter before the air is discharged up exhaust stacks. SO((2)) is produced when the fuel source (e.g., coal, which is the primary fuel in the United States ((1)) contains sulfur. Plants producing Portland cement have unique processes and design characteristics, and the concentrations of environmental contaminants fluctuate, depending on weather conditions and the amount of production. Therefore, SO((2)) levels may vary from plant to plant and from day to day. Results of the NIOSH investigations follow.

Iowa: On January 16, 1980, NIOSH received an HHE request from the labor union representing cement workers at a Portland cement plant in Mason City, Iowa. Some workers, especially among the labor and maintenance crews, had experienced burning eyes, sore throat, chest tightness, cough, headache, nausea, frequent colds, shortness of breath, and dizziness for 5-6 months. The NIOSH team took samples for possible exposures to SO((2)) emanating from the kiln exhaust system; analysis showed SO((2)) concentrations ranging up to 1.03 parts per million (ppm). The coal burned in this plant had a mean total sulfur content of 0.7%.

Oklahoma: On June 6, 1981, NIOSH received an HHE request from a labor union representing workers at a Portland cement plant in Tulsa, Oklahoma. Complaints among workers had included eye or nose irritation, sore throat, dizziness, headache, and chest pain or tightness for 6-8 months. Samples taken at various locations around the plant showed SO((2)) concentrations from 0.2 ppm to 1.8 ppm. The coal burned in these kilns had a mean sulfur content of 1.6%. Reported by Div of Respiratory Disease Studies, National Institute for Occupational Safety and Health, CDC.

Editorial Note

Editorial Note: Workers engaged in occupations involving exposures to SO((2)) greater than 10 ppm show evidence of mucous-membrane irritation and reflex bronchoconstriction with increased airway resistance (2-5). The current Occupational Safety and Health Administration standard for occupational exposure to SO((2)) establishes a permissible exposure limit (PEL) of 5 ppm as an 8-hour time-weighted average. In 1980, the American Conference of Governmental Industrial Hygienists (ACGIH) recommended lowering the PEL to 2 ppm, because, although SO((2)) may not produce subjective irritation in acclimatized workers, it can cause bronchoconstriction and a temporary decrease in pulmonary function (6). ACGIH also recommends a 15-minute, short-term exposure limit of 5 ppm. Based on studies indicating chronic respiratory disease among workers exposed to 1-4 ppm SO((2)), NIOSH recommends a 10-hour time-weighted exposure limit of 0.5 ppm (7). No effects were noted among steel workers exposed to a mean SO((2)) concentration of 0.35 ppm (8).

In both investigations reported here, area samples were collected only in locations suspected of having elevated SO((2)) concentrations, thus representing the worst case conditions for the particular shift sampled. Highest SO((2)) concentrations at both facilities were found around the baghouses. Because the HHEs were conducted over short periods (1-2 days), changes in concentration due to process variations, atmospheric conditions, or the sulfur content of the kiln fuel could not be detected. In addition, samples were collected over 5-6 hours and reflect the average concentration during this period (9).

In a stratified, randomized cross-sectional study of the Portland cement industry previously conducted by NIOSH, 92 samples for SO((2)) were collected from 13 plants. Only one sample exceeded 0.5 ppm, the NIOSH-recommended exposure criterion. Thus, SO((2)) concentrations in Portland cement plants appear to be generally below levels documented to cause acute mucous-membrane irritation or to exacerbate chronic respiratory disease. However, the results reported above demonstrate that these workers are potentially exposed to SO((2)) from the exhaust gases of kilns, especially those fueled by coal containing sulfur.

Workers at Portland cement facilities, particularly those burning fuel containing sulfur, should be aware of the acute and chronic effects of exposure to SO((2)), and peak and full-shift concentrations of SO((2)) should be periodically measured.

References

1. Shreve R, Brink J. Chemical process industries. New York: McGraw-Hill, 1977:156-2.

2. National Institute for Occupational Safety and Health. Occupational exposure to sulfur dioxide; criteria for a recommended standard. National Institute for Occupational Safety and Health, 1974.

3. Kehoe RA, Machle WF, Kitzmiller K, LeBlanc TJ. On the effects of prolonged exposure to sulphur dioxide. J Ind Hygiene 1932;14:159-73.

4. Skalpe IO. Long-term effects of sulphur dioxide exposure in pulp mills. Br J Ind Med 1964;21:69-73.

5. Ferris BG Jr, Burgess WA, Worcester J. Prevalence of chronic respiratory disease in pulp mills and a paper mill in the United States. Br J Ind Med 1967;24:26-37.

6. American Conference of Governmental Industrial Hygienists. Sulfur dioxide, in documentation of the threshold limit values for substances in workroom air. 3rd ed. Cincinnati, Ohio: American Conference of Governmental Industrial Hygienists, 1971, pp. 238-9.

7. National Institute for Occupational Safety and Health. Testimony at OSHA hearings on sulfur dioxide (May 12, 1977).

8. Lowe CR, Campbell H, Khosia T. Bronchitis in two integrated steel works. 3. Respiratory symptoms and ventilatory capacity related to atmospheric pollution. Br J Ind Med 1970;27:121-9.

9. National Institute for Occupational Safety and Health. Manual of analytical methods; sulfates, sulfites, and sulfur dioxide, Vol. 5, Physical and Chemical Analytical Methods 1979:268.

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