T. Oldham, M. Harrison, J. Jankovic, Oak Ridge National Laboratory, Oak Ridge, TN.
Numerous manufacturers currently produce oxygen monitoring equipment for industrial safety applications. Due to their small size and low cost, most of these instruments utilize some form of electrochemical cell as their oxygen sensor. Under most conditions, these sensors perform well; however, questions regarding the performance of these sensors in the presence of large amounts of helium or other light gases have been noted by different investigators. Two types of diffusion barriers (capillary and membrane) are typically used with electrochemical oxygen sensors. This study measured the accuracy of different manufacturers’ oxygen monitors, utilizing both types of diffusion barriers, when exposed to different concentrations of helium produced at varying leak rates. Many types of laboratories and high tech businesses use liquid helium refrigeration systems for super cooling instruments and equipment. The potential for an accidental release involving large amounts of helium into the atmosphere is very real in facilities of this type. Oxygen sensors of the type discussed are typically used to monitor these facilities for safe oxygen levels. The results of this study show that under certain conditions, some of the sensor designs significantly overestimate the true oxygen concentrations. This over-response could potentially allow employees to enter a hazardous, oxygen deficient environment without warning. The ability to accurately monitor oxygen concentration is crucial to the safety and health of employees. This study will provide industrial safety and health professionals with information on the effects of helium on a variety of commonly used oxygen monitors
R. McCleery, L. Tapp, J. McCammon, K. Dunn, NIOSH, Cincinnati, OH.
Introduction: NIOSH was asked for assistance in evaluating carbon monoxide (CO) concentrations in the Bridgewater Channel in Lake Havasu City (LHC), Arizona, over the Memorial Day weekend, May 23–26, 2003. The request expressed concern about CO overexposures among LHC police and Emergency Medical Service (EMS) personnel who patrol the waterway during holidays for as much as 10 hours per workshift.
Methods: Real-time CO monitoring was conducted on podium and EMS personnel with additional general area sampling in and around the channel. Daily pre-shift, mid-shift, and post-shift questionnaires in conjunction with exhaled breath CO measurements were also conducted. Questionnaires included information on work duties and location, tobacco use, and surveys of potential CO exposure symptoms.
Results and Conclusions: There were 78 total workshifts where real-time CO monitoring was performed. Of those 78 workshifts, 54 exceeded the NIOSH ceiling limit of 200 ppm, 64 exceeded the ACGIH excursion limit of 125 ppm, 7 exceeded the OSHA PEL of 50 ppm, 17 exceeded the NIOSH REL of 35 ppm, and 33 exceeded the ACGIH TLV® of 25 ppm. There were 81 total workshifts where exhaled breath analysis and questionnaires were conducted. Of those 81 workshifts, 63 were with nonsmoking participants. Among the 63 nonsmoking participants, 42 had a post-shift percent carboxyhemoglobin (% COHb) at or above the ACGIH BEI® of 3.5%, with some levels approaching 15%. For 40 of the 81 workshifts with pre- and post-shift measurements, the cross-shift difference was at or above 3.5%. The questionnaires indicated that the most frequently reported symptom was headache, followed by fatigue or weakness, visual disturbances, and dizziness. NIOSH investigators concluded podium and EMS personnel working in the canal are exposed to CO concentrations approaching and/or exceeding relevant evaluation criteria.
V. Murray, University of Texas Health Science Center-Houston, Sugar Land, TX.
Toll roads are typically situated to alleviate existing traffic congestion. As a result, these highways often experience relatively high vehicular traffic density. More importantly, toll booth attendants perform their work activities in this environment and are potentially exposed to high levels of vehicular emissions. Previous studies have characterized toll booth attendants’ exposures to pollutants such as carbon monoxide and particulate matter, but only one other study (performed outside the U.S.) has addressed exposure to volatile organic compounds (VOCs). Long-term exposure to VOCs, even at moderate levels, may cause an increased risk of adverse health effects, which can include cancer, respiratory and central nervous system problems, exacerbated allergies, and adverse neurological, reproductive, and developmental effects. The main purpose of this study was to characterize typical workshift exposures to a number of automotive-related VOCs for a group of toll booth attendants manning both entrance and exit ramp booths at one of the busiest toll stations in Houston. A secondary purpose was to evaluate the effect of toll booth air-conditioning on the reduction of outside VOC concentrations.
Exposure measurements were performed with diffusive air samplers placed inside and outside exit and entrance ramp toll booths during morning and afternoon/evening workshifts, during two different work weeks. Outside median concentrations for methyl tertiary-butyl ether, benzene, toluene, ethylbenzene, m,p-xylene, o-xylene, 1,3,5-trimethylbenzene, 1-ethyl-2-methylbenzene, and 1,2,4-trimethylbenzene equaled 7.11, 3.90, 3.61, 1.06, 2.94, 0.98, 0.63, 0.59, and 1.19 µg/m3, respectively. Although outside levels were statistically similar at both booths, indoor/outdoor concentration ratios were typically lower for the entrance ramp booth, suggesting a difference in effectiveness of the air-conditioning system. Regression analyses indicated a greater effect of wind velocity and temperature than traffic count on outdoor concentrations.
M. Finley, E. Page, NIOSH, Cincinnati, OH.
Investigators from the National Institute for Occupational Safety and Health (NIOSH) responded to a confidential request for a health hazard evaluation from printing press operators at a large Midwestern printing facility. These employees were experiencing symptoms they believed were related to their exposure to inks and solvents. NIOSH investigators visited the facility to characterize workers’ exposures, evaluate symptoms, and provide recommendations to minimize hazardous exposures. During the survey, personal breathing zone air sampling was conducted for trimethylbenzenes and trichloroethylene (results ranged from 0.3 to 9.5 parts per million (ppm) and not detected to 26 ppm, respectively). The NIOSH recommended exposure limit (REL) for both of these chemicals is 25 ppm as an 8-hour time-weighted average. Only one trichloroethylene result exceeded the REL. Area air samples were collected for 2-butoxyethanol, carbon monoxide (CO), and ozone. Concentrations of 2-butoxyethanol ranged from 0.2 to 1.2 ppm, below the REL of 5 ppm, while CO results ranged up to 17 ppm, below the REL of 35 ppm. Ozone was not detected. Noise dosimetry revealed that 12 of 13 employees monitored exceeded the NIOSH REL of 85 dBA. Questionnaires were administered to press operators and office workers and these two departments were then compared on age, tenure, gender, smoking, atopy, exposures, and outcome variables. There was a significantly higher prevalence of rash/skin irritation on hands or arms, and burning/runny nose among press operators. There was also a higher prevalence of work-related wheezing, burning/watery eyes, and sore throat among press operators, but this was not statistically significant. NIOSH recommendations include instituting a hearing conservation program, replacing certain solvents, enforcing the use of appropriate gloves, and covering unused solvent containers. Future activities include additional air sampling, audiometry, and biological monitoring to investigate the synergistic relationship between exposure to noise and solvents.
R. Sollberger, R. Tubbs, R. McCleery, C. Achutan, M. Rodriguez, NIOSH, Cincinnati, OH.
NIOSH conducted a health hazard evaluation during cutting of cement tiles at a home construction site to assess worker exposures to noise, carbon monoxide (CO), respirable and total dust, and respirable silica. Tiles consisted of up to 75–80% by weight crystalline silica and were cut using portable gas-powered saws. On two consecutive days, full-shift PBZ samples were collected on eight workers to assess noise and CO exposures, and on 16 to 19 workers for respirable dust, total dust, and silica. A questionnaire administered to the workers asked for job information and health symptoms. During the evaluation, employees wore hard hats and safety glasses; some also wore disposable dust respirators, but none used hearing protection. All workers evaluated exceeded the NIOSH Recommended Exposure Limit (REL) for noise of 85 dBA, for an eight-hour time-weighted average (TWA). The respirable crystalline silica exposures ranged from 0.03 mg/m3 to 0.32 mg/m3, with 88% exceeding the NIOSH REL of 0.05 mg/m3. Thirteen of the 16 (81%) workers’ silica exposures exceeded the OSHA Permissible Exposure Limit, and 75% exceeded the ACGIH Threshold Limit Value. Total dust exposures ranged from 0.71 mg/m3 to13.01 mg/m3 and respirable dust exposures ranged from 0.23 mg/m3 to 2.31 mg/m3. One worker exceeded the NIOSH ceiling level of 200 ppm for CO, but none exceeded the NIOSH REL-TWA of 25 ppm. Fourteen of the 24 workers (58%) were experiencing respiratory symptoms that could be associated with workplace exposures to dust. Many workers lacked knowledge about the presence of silica in the tiles and were not familiar with the hazards associated with exposure to respirable silica. Recommendations were made to improve training, implement engineering controls to reduce noise, dust, and silica exposures, and use personal protective equipment.
D. Almaguer, R. Streicher, G. Burroughs, M. Ernst, R. Kovein, S. Shulman, NIOSH, Cincinnati, OH.
A study was conducted to evaluate potential worker exposures to 4,4’-diphenylmethane diisocyante (MDI) during the application of spray-on truck bed-liners. The Washington State Department of Labor and Industry recently observed MDI exposures in this industry and expressed concerns to NIOSH about excessive occupational asthma claims. The spray-on bed-liner industry is rapidly growing and dominated by small business entities. It has been estimated there are approximately 3000 bed-liner shops in the U.S. The process is analogous to undercoating and involves the application of an aerosolized two-part polyurethane or polyurea coating to the surface and walls of pick-up truck beds to provide a protective non-skid coating. Part A is a polymeric diisocyanate with varying percentages of MDI monomer, MDI prepolymer, and polymeric MDI. Part B is a polyol resin that reacts with the diisocyanate. The two components are pumped to a spray gun mixing chamber and sprayed at sufficient velocity to cause atomization. MDI samples were collected at six spray-on bed-liner facilities to determine MDI concentrations within the spray booths and adjacent areas. Samples were collected at a flow rate of 1 liter per minute (lpm) according to NIOSH Method #5525. The sampling train consisted of an impinger containing a solution of 1-(9-anthracenylmethyl)piperazine (MAP) reagent in butyl benzoate followed by a 37-mm two-piece filter cassette containing a glass fiber filter impregnated with solid MAP. Preliminary results indicate that MDI concentrations within the facilities ranged from non-detectable to 5.2 mg/m3, some exceeding the OSHA ceiling limit of 0.2 mg/m3. Applicators wore supplied-air respirators. These results show that ventilation must be improved before allowing relaxation of personal protective equipment requirements.
L. Burrelli, M. Nealley, M. Plisko, J. Spencer, Environmental Profiles Inc., Baltimore, MD.
Mechanics commonly use petroleum distillate-based solvents to penetrate and dislodge rusty bolts, nuts, and other metal parts during maintenance activities. Some commercial preparations of the petroleum-distillate product have been reported to contain varying quantities of benzene. The purpose of this study was to determine the exposure of a mechanic and his helper to benzene vapors when using commercially-available petroleum distillate solvents spiked with various concentrations of benzene. In order to evaluate these exposures, three batches of penetrating solvent were spiked with known weight percentages of benzene. Specifically, preparations of the solvent/benzene solutions were made in approximate 1, 7, and 30% concentrations of benzene by weight. The actual weight percentages of the prepared mixtures were determined by laboratory analysis. The results demonstrate that the mechanic and helper were not exposed to benzene in air at levels greater than the current OSHA eight-hour TWA permissible exposure limit of 1 part per million (ppm). Additionally, 27 air samples were collected for 15-minute short-term exposure limit (STEL) determination from the mechanic and helper during the entire study. One sample of the 27 collected and analyzed marginally exceeded the OSHA 15-minute STEL of 5 ppm. The one sample that exceeded this limit was reported at 5.03 ppm and was collected from the mechanic during the work task associated with the use of the 6.8% solvent/benzene.
M. Plisko, J. Spencer, L. Burrelli, Environmental Profiles Inc., Baltimore, MD.
Measurement and monitoring of occupational exposure have traditionally been performed using validated air sampling and analytical methods. Physical-chemical mathematical models have also been used for occupational exposure assessment, most often in circumstances where air monitoring is either not possible or would only provide limited data due to minimal available resources.
Mechanics commonly use petroleum distillate-based solvents to penetrate and dislodge rusty bolts, nuts, and other metal parts during maintenance activities. Commercial preparations of a commonly used petroleum-distillate product have been reported to have contained varying quantities of benzene. The purpose of this study was to use predictive modeling in conjunction with traditional air monitoring to predict and determine the exposure of a mechanic and his helper to benzene vapors when using a benzene-containing petroleum solvent.
The benzene exposure to the mechanic and his helper was evaluated using traditional breathing zone air monitoring. The near field-far field physical-chemical mathematical model was used to predict the exposure concentration. Such methods were used in tandem since only one exposure period was monitored and the potential variability of the exposure data was unknown. Furthermore, variables such as quantity of solvent being used and air flow through the near-field may be described when modeling the work practices but are not necessarily accounted for when evaluating the results of air sampling.
The results of the predictive modeling were within a factor of four of the actual measured results. For the purposes of this evaluation, neither the breathing zone determination nor the mathematical model was considered to be more appropriate than the other. Each of these methods was considered an important tool for characterizing or predicting the potential and measured exposure.
A. Petty, Bechtel Jacobs Company LLC, Piketon, OH.
Industrial hygiene air sampling and urinalysis biological monitoring to quantify inorganic arsenic exposures were conducted on a workforce performing scrap metal size reduction and disposal at a former uranium enrichment facility. Personal air sampling and inorganic arsenic in urine results are reported for concurrent 20 and 17-month periods, respectively. Mean arsenic job concentrations and 10-hour time-weighted average (TWA) concentrations were found to be elevated in welders, compared with other worker classifications. No worker classifications had mean 10-hour TWA concentrations exceeding the OSHA Permissible Exposure Limit of 7 µg As/m3, adjusted to a 10-hour TWA using the Brief and Scala Model. Mean inorganic arsenic in urine concentrations, measuring inorganic arsenic and the metabolites monomethylarsonic acid and dimethylarsinic acid, reported both as speciated (AsITM) (mean = 10.51 µg AsITM/liter) and creatinine-corrected concentrations (mean = 9.23 µg AsITM/gram creatinine) were found to be comparable with concentrations from nonoccupationally exposed general public populations reported in the literature. A total of 1211 urine specimens (88.01% of all acceptable creatinine concentration specimens) had speciated inorganic arsenic less then the detectable limit of <10 µg AsITM/liter. No significant correlation or regression relationships were found in comparing arsenic air concentrations, both as job and 10-hour TWA concentrations, and inorganic arsenic in urine concentrations, both in speciated and creatinine-corrected units of measurement. The reported mean inorganic arsenic in urine concentrations were well below both the ACGIH Biological Exposure Index of 35 µg AsITM/liter and the Lauwerys and Hoet Temporary Maximum Permissible Concentration of 30 µg AsITM/gram creatinine. This result demonstrates the effectiveness of an exposure control program incorporating all aspects of the OSHA Regulation for Inorganic Arsenic in General Industry, particularly a respiratory protection program, in reducing inhaled, and ultimately, excreted arsenic levels.
M. Methner, NIOSH, Cincinnati, OH.
The National Institute for Occupational Safety and Health (NIOSH) was asked to evaluate worker exposure to inorganic arsenic fume during torch-cutting operations in a scrap yard located within a former uranium enrichment facility. Arsenic, a recognized carcinogen, was a contaminant that was inadvertently introduced into the enrichment system and subsequently bonded to the internal surfaces of process equipment. When the enrichment system formally ceased operations, process components needed to be dismantled and reduced in size via torch-cutting prior to off-site disposal. As a result of the torch-cutting, arsenic fume is released and employees are exposed. NIOSH reviewed the site’s arsenic exposure control plan and the historical air sampling and biological monitoring data, observed work practices, examined the local exhaust ventilation system used for fume control, and collected Ghostwipe® samples from various surfaces as a qualitative indicator of potential sources of arsenic exposure. Major findings of this study were: (1) wipe samples indicated “freshly cleaned” respirators had measurable levels of inorganic arsenic (range = 0–16 micrograms/ wipe); (2) the local exhaust ventilation system needed maintenance (e.g., hole found in duct); (3) the ventilation hood did not provide effective fume capture; and (4) workers did not wear respirators at all times when working within the arsenic control area. Recommendations included improving the current ventilation system by moving the exhaust hood closer to the point of fume generation (1–2 feet away), installing a flange on the hood to increase fume capture, continue monitoring air and urine levels of arsenic, encouraging employees to shave facial hair daily to assure better respirator fit, and develop a more effective respirator washing procedure.
T. Perng Jy, L. Chuh Lun, National Cheng Kung University, Tainan, Taiwan, Republic of China.
This study used the Monte Carlo method to determine the most significant environmental factor associated with thermal stresses imposed on workers in steel casting plants. Environmental samplings were conducted on the furnace area at each of the five selected steel casting plants. Four environmental factors, including the ambient air temperature (Ta), globe temperature (Tg), air velocity (Va), and relative humidity (RH), were measured continuously during a working shift. In addition, 5–7 furnace workers were chosen from the five selected casting plants (total = 27 workers) to estimate their metabolic rates by using a real-time heart rate monitor. All measured data were applied to a predicted heat strain (PHS) model proposed by ISO in 2003 to determine the allowable exposure time (AET) for each selected worker. The sensitivity of each measured environmental parameter on determining AETs was estimated by using the Monte Carlo method. Results show that the mean Ta, Tg, RH, and Va measured from the furnace of the five selected casting plants were 38.34±3.89°C, 42.26±4.56°C, 55.53±3.35%, and 0.71±0.64 m/s, respectively. Workers’ metabolic rates were found ranging from 128 to 194 W/m2. After being analyzed by the PHS model, this study yielded the mean AET (= 232.6±37 minutes), indicating that furnace workers might be exposed to excessive thermal stresses while continuously performing their jobs at the furnace area. We further conducted the Monte Carlo sensitive analysis and found out that Tg was the most significant environmental factor that affected furnace workers’ AETs. The above result suggests that the control of the environmental factor of Tg would be the most efficient way to reduce workers’ thermal stresses.
L. Chuh Lun, T. Perng Jy, National Cheng Kung University Medical College, Tainan, Taiwan, Republic of China.
This study simulated real exposure scenarios in a thermal exposure chamber to assess the validity of the predictive equation adopted in the predicted heat strain (PHS) model proposed by ISO for determining the heat flow associated with respiratory convection (Cres). The simulated real thermal exposure scenarios were based on the environmental monitoring results obtained from two steel casting plants and physiological monitoring results from 97 steel casting workers. In the thermal exposure chamber, the mean simulated environmental conditions were: Ta 34.39±4.51°C, Tg 37.27±4.45°C, Pa 2.2±1.1 kPa, and Va 0.61±0.51 m/s, and the simulated workloads were: heavy 171 kcal/hr, middle 302 kcal/hr, and 403 kcal/hr. The “real Cres” (Cres-real) were directly estimated from the principle algorithm based on workers’ body mass, height, V, and Tex. The resultant Cres-real was then compared with that obtained from PHS model (Cres-model). Results show that the resultant Cres-models were significantly different from the corresponding Cres-reals (paired-t test, p<0.0001). We further developed an empirical predictive algorithm for Cres according to all measured data. This study yielded: Cres = 0.0014×M × (Tex-Ta)-0.047). The predicted values obtained from the above proposed model were not significantly different from the corresponding Cres-real values (paired-t test, p = 0.82) with a correlation coefficient 0.99. The above results suggest the need for modification of ISO Cres predictive equation under our prescribed testing ranges, and our proposed equation would provide a better estimation for Cres.
N. Goyer, S. Buissonnet, B. Roberge, IRSST, Montreal, PQ, Canada.
In the context of a study of the impact on worker health and the financial impact of a reduction in the current threshold limit value (TLV®) ceiling of 2 ppm for formaldehyde to a TLV® ceiling or time-weighted average (TWA) of 1, 0.75, or 0.3 ppm, the exposure of pathology laboratory workers in Québec hospitals was evaluated. The aim of the study was also to document the emission sources and hazardous tasks in order to evaluate the costs of corrective measures.
The study was carried out in 10 laboratories. All the tasks performed by pathologists, technologists, technical assistants, and secretaries where formaldehyde was present in the air were evaluated. For the TWA, samples were collected on XAD-2 polymer tubes impregnated with hydroxymethyl piperidine, at 0.2 L/min for periods representative of the work carried out during the workshift. For the ceiling exposure and identification of emission sources, readings were taken by an infrared analyzer equipped with a photoacoustic detector, Innova 1312.
The results demonstrated that the TWA ranged from 0.01 to 0.92 ppm for pathologists, to 0.76 ppm for technologists, to 0.21 ppm for technical assistants, and 0.03 ppm for secretaries. The ceiling value of 2.0 ppm was reached for several tasks including macroscopy, the disposal of specimens and waste solutions, and maintenance of the tissue preparer. Specimen storage and medical waste garbage pails were also formaldehyde emission sources.
The main determinants of exposure were: the presence and efficiency of local exhaust systems, the efficiency of the general ventilation, the number of workstations in the same room, the size and number of fixed anatomical parts to be handled, the concentration of the formaldehyde solution used, and the work methods. Control aspects must take these factors into account and are at the same time of a technical and organizational nature.
N. Goyer, S. Buissonnet, E. Pellerin, B. Roberge, IRSST, Montreal, PQ, Canada.
In the context of a study of the impact on worker health and the financial impact of a reduction in the current threshold limit value (TLV®) ceiling of 2 ppm for formaldehyde to a TLV® ceiling or time-weighted average (TWA) of 1, 0.75, or 0.3 ppm, the exposure of Québec embalming workers was evaluated. The aim of the study was also to document the emission sources and hazardous tasks in order to evaluate the costs of corrective measures.
The study was carried out in four embalming rooms. All the steps in which formaldehyde was used were evaluated. For the TWA, samples were collected on XAD-2 polymer tubes impregnated with hydroxymethyl piperidine, at a flow of 0.2 L/min for periods representative of the work carried out during the workshift. For the ceiling exposure and identification of emission sources, readings were taken by an infrared analyzer equipped with a photoacoustic detector, Innova 1312.
The results demonstrated that the TWA were generally under the value of 0.3 ppm for embalmers except for difficult cases such as a decaying or autopsied body. However, the ceiling value of 2.0 ppm was often exceeded. In addition to emissions from the body, solution preparation and the injection device were important formaldehyde emission sources, particularly when the device was being filled.
The main determinants of exposure were: the physical parameters of the body (condition, corpulence, medical history), the time between the patient’s death and embalming, the step in embalming, the formaldehyde index of the chemical product used, the number of bodies handled simultaneously, and the type and efficiency of the ventilation used. Control aspects must take these factors into account and are at the same time of a technical and organizational nature.
A. Lehocky, Vandebilt University, Nashville, TN.
Side-by-side comparisons have been performed between DNPH (2,4-dinitrophenolhydrazine) tubes (SKC 226-119) with low sampling pumps (GilAir-5, Sensidyne) and Assay Technology 571AT badges for monitoring formaldehyde in a gross anatomy laboratory and embalming facility. The gross anatomy laboratory contains 21 stations, 104 students, and 5 instructors, and the embalming facility consists of a dedicated room with a chemical mixing station. The embalming fluid used to preserve cadavers consists of formaldehyde, phenol, ethanol, glycerin, and water. Monitoring was conducted on medical students, instructors, and embalmers using a combination of side-by-side measurements between the two sample media. All badges and tubes were analyzed using the NIOSH 2016 method for formaldehyde. Monitoring times varied between 15 minutes and 5 hours. In addition, real-time measurements were conducted with a Miran 205B SapphIRe (Thermo Environmental Instruments) infrared spectrophotometer at every station in which side-by-side was conducted. The concentration of formaldehyde varied depending on the area of the cadaver in which was being studied. Peak concentrations were observed during dissection of the abdomen region. The instructors were observed with the highest level of exposure during short and long monitoring periods. The highest concentrations of formaldehyde were observed during embalming activities, however, these are generally short-lived because of the limited numbers of cadavers embalmed during the academic year.
B. Beamer, D. Watkins, S. Shulman, A. Maynard, NIOSH, Cincinnati, OH.
It is estimated that more than 1.7 million workers in the U.S. have been exposed to respirable crystalline silica, with a large percentage having been exposed to silica concentrations higher than limits set by current standards and regulations. The purpose of this study is to characterize the use of water-type engineering controls to reduce exposure to respirable crystalline silica for construction workers engaged in the task of brick cutting.
Since data concerning the efficacy of engineering controls collected at work sites is often confounded by variations like wind, worker skill level, etc., experimentation was conducted in a laboratory environment. A completely enclosed testing chamber housed the brick-cutting saw. Respirable dust concentrations were measured by the Model 3321 Aerodynamic Particle Sizer® Spectrometer. Specifically, the laboratory experiment was designed to compare dust suppression of water misting with conventional flooding techniques. Three flow rates of the brass atomizing nozzles were used for making this comparison: low (4.8 gallons per hour), medium (8.6 gallons per hour), and high (17.3 gallons per hour). The flow rate for flooding was 48 gallons per hour.
The experiment consisted of five replications of five samples each (low-misting, medium-misting, high-misting, flooding, and no control). The order of sampling within each replicate was completely randomized. Results showed that low-misting nozzles reduce respirable dust levels by about 62%, mid-misting nozzles by about 71%, high-misting nozzles by about 82%, and flooding by about 92%. Based on these results, it may be feasible to use misting to control respirable silica dust instead of flooding. This strategy is of practical interest to the construction industry which must frequently limit the amount of water used on construction sites for a variety of reasons.
M. Pannell, Los Alamos National Laboratory, Los Alamos, NM.
Potential employee exposure to crystalline silica must be considered throughout the construction, mining, and agricultural industries. Although environmentally ubiquitous and long known as a lung hazard, the ability to accurately quantify worker exposure remains problematic. This paper identifies four aspects of crystalline silica exposure assessment that present potential pitfalls, and subsequently suggests means of resolution for each. The identified pitfalls are: (1) the use of the OSHA calculated permissible exposure limit, (2) sampling, (3) analysis, and (4) control measures. The OSHA calculated permissible exposure limit, as defined in 29 CFR 1910.1000, Table Z3, allows immediate, on-site gravimetric analysis and reduces the cost and delay of comprehensive x-ray diffraction analyses. However, the ability to acquire a representative x-ray diffraction sample is difficult and there are potential variations in the reference constituents among the four prescribed sources. Facilities following ACGIH recommendations face additional concerns with the difference in respirable fraction value component of the calculated permissible exposure limit as well as the threshold limit value for quartz. Sampling presents the second presented aspect of crystalline silica exposure assessment. These include determining the type of cyclone, flow rate, the sample location, and collecting a representative sample. Sample analysis is the third aspect discussed. Specific components discussed are x-ray diffraction analysis variability, gravimetric analysis, sufficiency of sample loading, filter dessication, and sample mass losses. The final aspect discussed in this paper is the use of control measures, including dust suppression, the inherent control ability of equipment, and personal protective equipment. Recommendations are presented to minimize the variability within each of the presented problem components, designed to enhance the industrial hygienist’s ability to more accurately assess worker exposures to crystalline silica. The recommendations presented are based on 1500-plus samples in numerous construction, maintenance, and mining activities.
A. Yassin, R. Tingle, U.S. DOL/OSHA, Washington, DC.
The purposes of this study were (a) to measure concentration of crystalline silica (respirable) dust exposure levels among U.S. workers; (b) to identify high-risk occupations and industries; and (c) to conduct time trends analyses on silica dust exposure levels for time-weighted average (TWA) measurements. Compliance inspection data that were taken from OSHA Integrated Management Information System for 1988–2003 (n = 7055) were used to measure the crystalline silica dust exposure levels among the U.S. workers. Log-linear trend regression analysis was used to assess time trends in exposure measurements of silica. The overall geometric mean of silica dust level for an 8-hour personal TWA measurement was 0.038 milligrams per cubic meter (mg/m3). This level was well below the applicable exposure guidelines, including the National Institute for Occupational Safety and Health recommended exposure limit of 0.05 mg/m3 and the American Conference of Governmental Industrial Hygienists threshold limit of 0.1 mg/m3. Mining industry had a geometric mean silica exposure level of 0.285 mg/m3 compared with 0.057 mg/m33 for the construction industry. Service industry combined with other industries had the lowest geometric mean crystalline silica exposure level of 0.025 mg/m3 for an 8-hour TWA measurement. Although crystalline silica exposure levels declined in some industries, the results showed an upward trend in the silica respirable dust exposure levels in certain industries and occupations.
E. Demchuk, V. Murashov, M. Harper, NIOSH, Morgantown, WV.
Inhaled crystalline silica is commonly viewed as an increased risk factor for pulmonary fibrosis, pneumoconiosis, silicosis, and lung cancer, although the mechanisms involved in silica-dependent lung injury are poorly understood. Based on the structural analysis of crystals and computational modeling, a new association between the structural specificity of silanol sites on silica surface and health effects of respirable silica is proposed. Silica surface accommodates two types of silanol sites. They are the Si-OH (single) and Si=(OH)2 (geminal) sites. It is found that unlike natural grown quartz or kaolinite, the surface of cleaved quartz is enriched with geminal silanol sites. An estimated concentration of 0.067 Ĺ-2 silanol sites on the conchoidal fracture of pure α-quartz is obtained. About 25% of these sites are geminal. In contrast, surfaces of pristine quartz crystals and kaolinite are found to be virtually free of geminal sites. Because of the higher calculated surface energy of geminal sites, it is proposed that the concentration of geminal sites on respirable particulate matter may be associated with the increased fibrogenic potential of crystalline silica. It is suggested that structural specificity of silanol sites on silica surface may be a factor deserving consideration in occupational risk assessment.
Posted May 30, 2004