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RESPIRABLE DUST Respirable Dust Evaluation of Two Portland Cement Operations -Part 2 part series, the authors study, discuss the r most recent study, and d ways to reduce respirable dust by Andrew B. Cecala, Robert i. Tlmko, Jeanne A. Zimmer and Edward D. Thlmons and total dust, free crystalline silica,1 alu minum, cobalt, magnesium, manganese, nickel, asbestos, nitrogen dioxide, oxides of sulfur, and other trace elements. n Part 1 of this series, the authors dis 1 Both personal and area sampling were Icussed a recent study that evaluated dust levels at two Portland cement operations performed during these evaluations. Medical testing of workers also was performed to to determine how measured dust levels determine the prevalence of respiratory dis relate to a dust standard change being pro ease within a few weeks ofthe environmental posed by the Mine Safety and Health analysis. For the medical testing, more than Administration (MSHA). These two opera 2,730 cement plant workers were analyzed tions differed in that one used the dry- and and compared to a control group of 755 the other the wet-processing technique. workers. The control group was composed At both operations, respirable dust mea of workers from 10 plants in various non surements were taken throughout the entire cement-type industries. This study also cement making process. In addition, mea looked at the smoking status of cement plant surements were taken on the perimeters workers, as well as for the control group. A of the properties to determine relative dust summary article on this research was pub quantities traveling toward adjoining resi lished in the British Journal of Industrial dential areas. Medicine (1988).1 Evaluations were performed at each oper In the course ofthis study, there were 1,011 ation during the summer and winter to com personal respirable dust samples taken and pare dust levels in both weather conditions. 211 personal total dust samples. The geo Area samples were collected to investigate metric mean dust concentration of the 1,011 problem areas with the goal of making rec personal respirable samples was 0.57 ommendations on ways to lower dust levels mg/m3, with 5% of the samples exceeding in areas with higher concentrations. the 5-mg/m3 level. The geometric mean dust Previous NIOSH study concentration for the 211 personal total dust samples was 2.90 mg/m3, with 19% of the From 1979 to 1982, the National Institute for samples exceeding the total dust standard Occupational Safety and Health (NIOSH) of 10 mg/m3. performed environmental studies at 16 Quartz was the only contaminant found cement operations throughout the United in excessive concentration. Quartz was States, selected by looking at factors such detected in 14.4% of the personal respirable as age of the operating kiln and the type dust samples when analyzed for crystalline of process used. During these evaluations, silica with a median concentration of 0.079 samples were collected and analyzed for mg/m3. Respirable quartz was found most various toxic agents, including respirable often in the quarry, primary crusher, prima ry grinding, and processing mills. The num ber of samples with detectable quartz var ied significantly among plants and was primarily believed to be correlated with vari ations in the raw material. No cristobalite was found in any Samples taken. The only other mention of a contaminant other than respirable/total dust and crys talline silica was a low level of hydrogen sul fide found at one operation. This was believed to be associated with the limestone quarry water. Little adverse effect of cement plant dust on respiratory symptoms and ven tilatory function was found in this study. However, the prevalence of radiographic abnormalities consistent with pneumoco niosis was low but significantly elevated from the norm. Considering the size of this study and the comprehensive nature of the expo sure sampling, the main concern in cement plants should be controlling total and res pirable dust levels, with special emphasis on controlling silica dust. Discussion The field evaluation portion of the more recent study was performed during an 18month period comparing dust concentra tions in both summer and winter conditions at a wet- and a dry-processing cement oper ation. This research effort was initiated in 1995 during a time when the Bureau of Mines was being eliminated. This impacted fund ing levels, thus affecting the number and locations of operations evaluated. Two evaluation sites were chosen to meet the research objectives, but it must be remembered that they provide a small pic ture of the industry as a whole. However, combined with the data from the earlier NIOSH study, it provides a meaningful look at dust levels in cement operations. Respirable dust concentrations at the var ious sampling locations measured at the dry processing operation ranged from 0.04 to 16.02 mg/m3. The average respirable dust concentration for both summer and winter surveys was 2.52 and 0.07 mg/m3 for the plant and environmental monitoring loca RESPIRABLE DUST tions respectively. The only location above the 5-mg/m3 average was the clinker cool ing tunnel, which averaged 16.02 mg/m3 dur ing the August survey. This value had a great impact on the overall plant average, raising it by 1.12 mg/m3. It should be noted that plant personnel are seldom in this tunnel, and when neces sary, it is normally not for extended periods of time. The main reason for high dust lev els at this location was due to the convey or line being located underground with no controls to clear the dust liberated during product conveying. There also were high dust readings at the feedside end ofthe kilns for the first few sampling segments during the August survey, which was due to a dust leak in the system. Once this problem was corrected, dust levels remained at less than 1.1 mg/m3 for the remainder of the test. There also were a few locations during the August survey that measured a higher dust reading for one sampling period than the others, and this was most likely due to a leak in the system or maintenance work. The firstfloor ball mill location recorded a 5.29-mg/m3 average for the first 7'/-hour sampling seg ment during the afternoon shift for the first day oftesting. A similar occurrence was mea sured at the second-floor ball mill location for nearly 7 hours during the second morn ing of testing and for the third sampling seg ment. There were no significant variations during the December analysis. Overall, dust levels at the dry-processing operation were at acceptable levels during the times ofthe two surveys based upon cur rent and proposed regulations. The only problem area was the clinker cooling tunnel location and recommendations to lower dust levels for this tunnel location will be given. Excluding the clinker cooling tunnel, the aver age plant dust concentration for all locations monitored for the two dust surveys was 1.40 mg/m3. The average environmental dust con centration was 0.07 mg/m3, which repre sented no significant contamination to occupied areas around the facility during the two surveys. Dust levels at the wet-processing opera tion ranged from 0.03 to 14.72 mg/m3 forthe summer and winter dust surveys with a plant average of 2.73 mg/m3 and an environmen tal average of 0.12 mg/m3. For the plant mon itoring locations, there were two locations with high respirable dust concentrations, the clinker slope conveyor and dischargeend fifth-floor kilns. Both of these locations were measuring dust generated by clinker product as it traveled on the beltway to the cooling storage area. During the summer analysis, both of these locations were impacted during cleanup work by the summer work force (11.88 and 14.72 mg/m3). Even though dust levels were lower during the winter analy sis at both of these locations, they were still at levels that would have significantly impacted a worker's dust exposure if they had spent a good portion of their work day in these areas (6.39 and 5.06 mg/m3). Recommendations to lower dust levels in these two areas will be presented. Dust levels at the remainder of the plant monitoring locations appeared to be at acceptable levels during the times ofthe two surveys based upon the proposed dust reg ulations. One concern identified at the sec ond plant was the housecleaning work crew. These workers are at high dust exposures while performing this type of work. This oper ation hired summer workers to primarily per form this housekeeping effort. There was very limited environmental monitoring done at this facility due to the weather conditions. Dust levels were record ed at four locations in July and two locations in February with an average dust exposure of 0.12 mg/m3. Although this value is slight ly higher than the average at the first plant, dust levels were still at levels that did not pose a problem to the neighboring commu nity during the evaluation period. Overall, the results of testing at both the dry- and wet-processing facilities were in line with the previous study performed by NIOSH. At the 16 operations analyzed in the previous study, there were a minimal num ber of personal dust samples that exceeded the recommended exposure for total dust, respirable dust, or silica, as well as a few operations with no over exposures. Again, the intent was to take area samples in an effort to investigate problem areas with the goal of being able to make recommenda tions on ways to lower dust levels in areas with higher dust concentrations. Recommendations Probably the area of greatest concern was confined areas used to transport product material within the process. This was seen at the clinker cooling tunnel at the first oper ation and clinker slope conveyor and dis charge-end fifth-floor kilns sample location at the second site. These locations were all similar in that product was being conveyed on a beltway in the confined area with very little or no supplied ventilation. Because of the lack ofventilation, any dust liberated remained trapped in the confined area and built up over time to significant dust lev els. These areas should be furnished with a ventilation system to provide fresh air to remove dust-laden air from the area. This air should be filtered through some type of col lecting system. While discussing ventilation, another rec ommendation is to provide total mill venti lation to targe structures. The use of this ventilation system can lower all workers' res pirable dust concentrations working with in these structures.2 This system uses a bottom-up approach. Clean make-up air is brought in at the base of the structure and sweeps upward through the building, clear ing dust-laden areas. This air is then dis charged at or near the top of the building where it will not contaminate plant person nel working outside. In addition, thermodynamic effects of the heat generated by plant equipment will assist the basic flow pattern of this venti lation system. This is probably the most costeffective system that a cement plant could (rations for all plant ^73 mg/m'fot ibe operations, respectively, well of 5 mj/m RESPIRABLE DUST implement to lower dust levels throughout any processing building. Dust reductions of 40% to 80% with these ventilation systems have been recprded at similar structures in other industries. This is the most cost-effec tive technique to achieve these types of dust reductions ifyou consider installation, main tenance, and operating costs. Another possible area for improvement is housekeeping practices. At the first opera tion, daily cleanup was observed in some areas of the plant and although this is good, sweeping and shoveling was the method used to perform this housekeeping effort. Sweeping and shoveling methods create a substantial amount of dust and expose the cleanup workers to higher dust levels. The first thing to do is to better seal leakage areas so housekeeping does not need to be per formed as often. When daily cleanup is performed, exhaust ventilation, or water wash-down methods are the preferred housekeeping techniques. Some operations use a centralized build ing vacuuming system with hookup ports located on various floors. This makes the clean-up process convenient and promotes good housekeeping. Many of these systems also have outside dust dropouts into truck tanks, which simplifies the disposal of the collected dust. At the second operation, a summer work crew was performing mill housekeeping and cleanup. Housekeeping should have been performed more often so that the build up was not so extensive. Dust levels were 46% and 66% higher during the summer survey at the two locations, directly impacted by the housekeeping. This had a great impact on dust exposure of the cleanup workers. Another recommendation is to provide cleanup and maintenance workers with pos itive-pressure-type respirators to increase their respiratory protection. Positive-pres sure respirators essentially eliminate the sealing concerns with a negative-pressure type while also providing for a more com fortable fit, especially during the hot sum mer months. Positive flow air purifying respirators should be either the half-mask or air-helmet type. It also should be stressed that a worker's dust exposure can be impacted by the way the job is performed. During a field study at a different operation, there was a sub stantial variation in the dust exposure of two workers performing the same job func tion based on differences in individual work practices or techniques. Even with the housekeeping practices, there can be a sig nificant difference in dust generated depending on how the worker performs the cleanup function. One last area deals with cleanliness of a workers' clothes. Researchers measured dust exposure increase of 10 times base levels resulting from a worker with soiled work clothes. Contaminated work clothes can be a major problem for some opera tions especially during the winter months, when workers wear heavy work coats. Many workers may wash their coats only periodically throughout the winter months, and these coats have the potential to be a significant source of personal dust expo sure. Operations should consider provid ing either disposable coveralls dr washing coveralls for their workers to minimize this dust source. Conclusion When this research was initiated in 1995, the dust standard was 10 mg/m3 total dust lim it with a proposed 5 mg/m3 respirable dust standard being proposed for metal/non metal operations. This also would provide insight into the potential impact of the dust standard change on the cement industry. For this study, dust measurements were taken at a dry- and a wet-processing oper ation for 48 to 68 hours of continuous sam pling during summer and winter surveys at both operations. Area dust measure ments were taken for this study using instantaneous and gravimetric sampling instrumentation, which eliminated many of the biases oftaking personal dust mea surements. This allowed for a determina tion of high-dust exposure areas of the plants. Recommendations were present ed on ways to reduce dust levels in these high-exposure areas. Overall, plant dust levels appeared to be at acceptable levels based on the proposed standard of 5 mg/m3 respirable dust. The average respirable dust concentrations for all plant monitoring locations for both sum mer and winter surveys were 2.52 and 2.73 mg/m3 for the dry- and wet-processing oper ations, respectively. There were a number of areas identified that were well above this average and could cause workers to be exposed to high dust levels if they spent a significant part of their work day in these areas. Recommendations were presented to lower dust levels in these areas, and some general recommendations were made for all workers. Environmental dust measurements also were taken on the perimeter of both plants near residential areas to determine relative dust levels traveling toward these areas. These measurements were not taken to indi cate any compliance with the U.S. Environmental Protection Agency regulations but just to indicate relative concentrations as compared to plant dust levels. In all cas es, respirable dust levels were at low levels and ranged from 0.03 to 0.19 mg/m3. Dust levels leaving the perimeter of the property ofthese two facilities were at acceptable lev els during all testing periods. As this dust continued to flow toward residential areas, it would continue to be further diluted as it became mixed with outside airflow. G All the authors are with the Dust and Toxic Substance Control Branch at the Pittsburgh Research Laboratory for the National Institute forOccupational Safety and Health. Andrew B. Cecala is a mining engineer; Robert J. Timko is a supervisory research physical scientist; Jeanne A. Zimmer is a physical scientist technician; and Edward D. Thimons is branch chief. ortland ffltish'journal of 5* pp 308-37$ AB, GW Klinowski, and ED "Reducing Respirable Dust tions at Mineral Processing Facilities Using Total Mill Ventilation System.'' Bureau of Mines PI 0460. Pittsburgh, PA, 1993.