THE EFFECT OF LOCAL EXHAUST VENTILATION CONTROLS ON DUST EXPOSURES DURING MASONRY ACTIVITIES. Gerry Croteau

Transcription

1 THE EFFECT OF LOCAL EXHAUST VENTILATION CONTROLS ON DUST EXPOSURES DURING MASONRY ACTIVITIES by Gerry Croteau A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science University of Washington 2000 Department of Environmental Health

2 University of Washington Graduate School This is to certify that I have examined this copy of a master's thesis by Gerry Croteau and have found that it is complete and satisfactory in all respects, and that any and all revisions required by the final examining committee have been made. Committee Members: Noah S. Seixas Steven E. Guffey Mary Ellen Flanagan Date:

3 Master's Thesis In presenting this thesis in partial fulfillment of the requirements for a Master's degree at the University of Washington, I agree that the Library shall make its copies freely available for inspection. I further agree that extensive copying of this thesis is allowable only for scholarly purposes, consistent with "fair use" as prescribed in the U.S. Copyright Law. Any other reproduction for any purposes or by any means shall not be allowed without my written permission. Signature Date

4 University of Washington Abstract THE EFFECT OF LOCAL EXHAUST VENTILATION CONTROLS ON DUST EXPOSURES DURING MASONRY ACTIVITIES by Gerry Croteau Chairperson of the Supervisory Committee Associate Professor Noah Seixas Department of Environmental Health This study assessed the effectiveness of commercially available local exhaust ventilation (LEV) systems for controlling respirable dust and crystalline silica exposures during concrete cutting and grinding activities. Work activities were performed by unionsponsored apprentices and included tuck point grinding a brick wall (angle grinder), surface grinding a concrete wall (surface grinder), paver block and brick cutting (masonry saw) and concrete block cutting (hand-held saw). In a randomized block design, implemented under controlled field conditions, three ventilation rates (0, 30 and 75 CFM) were tested for each tool/lev system. With the exception of the hand-held saw, the use of LEV resulted in a significant (p<0.05) reduction in respirable dust exposure. The mean exposure levels for the 75 CFM treatments were less than that of the 30 CFM treatments; However, differences between these two treatments were only significant for tuck point grinding (p<0.1) and paver block cutting (p<0.01). Although exposure reduction was significant (70-90% at the low ventilation rate and 80-95% reduction at the high ventilation rate), personal respirable quartz exposures remained very high ( x PEL at the low ventilation rate and 0.5 to 1.5 x PEL at the high ventilation rate). Nonetheless, this dust control alternative reduces the risk of workers developing disease, allows workers to use a lower level of respiratory protection, protects workers during short duration work episodes, may allow the effective use of administrative controls, reduces exposure to nearby workers and reduces clean-up associated dust exposures.

5 TABLE OF CONTENTS LIST OF FIGURES...II LIST OF TABLES... III INTRODUCTION...1 MATERIALS AND METHODS...6 STUDY LOCATION AND DESCRIPTION...6 EXPERIMENTAL DESIGN...7 VACUUM SOURCE...7 TOOLS EVALUATED AND WORK ACTIVITY DESCRIPTIONS...8 Angle Grinder...8 Surface Grinder...9 Masonry Saw...10 Hand-held Saw...11 EXPOSURE MONITORING...12 DATA ANALYSIS...13 RESULTS...20 EXPERIMENTAL CONDITIONS...20 PERSONAL DUST EXPOSURE RESULTS...21 RESPIRABLE DUST EMISSION RATE...22 EXPOSURE REDUCTION AND COMPARISON TO PELS...23 DISCUSSION...37 EFFECTIVENESS OF LEV SYSTEMS TESTED...37 EFFECT OF VENTILATION RATE ON DUST CONTROL EFFECTIVENESS...38 FACTORS AFFECTING LEV EFFECTIVENESS...40 EQUIPMENT PERFORMANCE...42 RESPIRABLE DUST EMISSION RATE...44 APPLICABILITY OF RESULTS TO FIELD CONDITIONS...45 CONCLUSIONS...47 LITERATURE CITED...48 APPENDIX A: FIELD MONITORING DATA: EXPERIMENTAL CONDITIONS (raw data)...51 APPENDIX B: FIELD MONITORING DATA: AIR SAMPLING...63 APPENDIX C: EXPERIMENTAL CONDITIONS (results)...75

6 LIST OF FIGURES FIGURE 1. Schematic of LEV testing work area...15 FIGURE 2. Angle Grinder...16 FIGURE 3. Surface Grinder...17 FIGURE 4. Masonry Saw...18 FIGURE 5. Hand-held Saw...19 FIGURE 6. Pers. resp. dust exp. resulting from tuck point grinding work activity...26 FIGURE 7. Pers. resp. dust exp. resulting from surface grinding work activity...27 FIGURE 8. Pers. resp. dust exp. resulting from paver block and brick cutting work activity...28 FIGURE 9. Pers. resp. dust exp. vs. emission rate for tuck point grinding...32 FIGURE 10. Pers. resp. dust exp. vs. emission rate for surface grinding...33 FIGURE 11. Pers. resp. dust exp. vs. emission rate for paver block and brick cutting...34 ii

7 LIST OF TABLES TABLE 1. Attributes of Tools and Construction Materials Used in Study...14 TABLE 2. Personal respirable dust exposure levels...25 TABLE 3. Linear Models Describing Log Respirable Dust Exposure Levels...29 TABLE 4. Respirable Dust Emission Rate...30 TABLE 5. Linear Models Describing Log Respirable Dust Emission Rate...31 TABLE 6. Comparison of Pers. Dust Exposure Levels to PEL and Reduction from LEV...35 TABLE 7. Resp. Quartz Pers. Exp. Levels and Comparison to Calculated OSHA Quartz PEL...36 iii

8 ACKNOWLEDGEMENTS The author acknowledges the important contributions of the following people and institutions: Laird Donaldson and Terry Hayes of the International Masonry Institute for providing technical expertise and assistance in setting up and conducting field work. Mark Maher and John Martin of the Western Washington Cement Masons Training Institute for providing technical expertise and a work area to conduct the project. Committee members Dr. Noah S. Seixas, Dr. Steve E. Guffey and Mary Ellen Flanagan for their insight, recommendations and availability. The field assistance provided by Ms. Flanagan was especially noteworthy. The Field Research and Consultation Group, especially Janice Camp and Tom Aquino, for assistance and use of field equipment. Dr. Gerald van Belle for timely advice regarding statistical analysis. The Environmental Health Laboratory for their skilled and timely sample analysis. Porter Cable, EDCO, Inc., and Wright-Lansdon Co., for loaning the LEV equipped tools. The National Institute of Occupational Safety and Health for the funding needed to carry out this project. My wife and children for their support and encouragement iv

9 INTRODUCTION 1 Exposures to crystalline silica can result from construction activities in which dust is generated during the cutting, grinding or drilling of concrete, brick, stone and similar building materials. This occupational exposure can result in silicosis, the development of discrete nodules formed in the lung parenchyma. As the condition progresses and the density of the fibrotic nodules increases, cardiopulmonary function is decreased, which can lead to death. Numerous studies have also shown an association between silica exposure and lung cancer resulting in silica being classified as a Type 1 carcinogen by IARC (IARC, 1997). Effective treatments for silicosis are non-existent, placing a high priority and importance on prevention through the reduction and elimination of respirable crystalline silica exposure. The results of several studies indicate that construction workers have an elevated risk of developing silicosis. In a mortality assessment of the U.S. construction industry (Robinson et al., 1995), the number of male construction worker deaths caused by silicosis was more than twice that of males employed in all industries (PMR = 210). A study conducted in Finland determined that construction workers had a standardized incidence ratio of 10.3 (95% CI ) for silicosis (Partanen et al., 1995). Construction workers from Hong Kong who died between 1979 and 1983 were found to have an elevated standardized mortality ratio for silicosis and tuberculosis mortality (Ng, 1988). An increased prevalence of silicosis and silica tuberculosis, as well as an excessive exposure to silica particulates was observed in caisson construction workers from Hong Kong (Ng, 1987). Overall, there have been relatively few studies addressing the incidence or prevalence of silicosis among construction workers due to the transient nature of the industry (Sullivan et al., 1995), lack of accurate silica exposure data even on a categorical basis (Oksa et al., 1992; Susi and Schneider, 1995), and apparent underreporting of new cases (Linch and Cocalis, 1994).

10 2 The U.S. Occupational Safety and Health Administration (OSHA) 8-hour time weighted average permissible exposure level (TWA-PEL) for crystalline silica is based on equation 1 (OSHA, 1989). OSHA PEL = 10 mg/m 3 /(% respirable quartz + 2) (1) The OSHA PEL corresponds to a respirable crystalline silica concentration of 0.1 mg/m 3 if the airborne respirable dust is 100 percent quartz. A more stringent 8-hour TWA of 0.05 mg/m 3 has been adopted as a threshold limit value (TLV) by the American Conference of Governmental Industrial Hygienists (ACGIH, 2000) and as a recommended exposure limit (REL) by the National Institute of Occupational Safety and Health (NIOSH, 1975). Given the serious and debilitating nature of silicosis, exposures should be reduced to the greatest extent feasible to reduce the risk of disease. The amount of crystalline silica a construction worker is exposed to is primarily dependent on the types of work performed, duration and frequency of work activities, construction material used, work location, and dust control measures (Lumens, 1997). Cutting, grinding and drilling of both concrete and stone are common activities that generate a considerable amount of dust. High airborne dust concentrations also result from clean-up activities, especially dry sweeping (Riala, 1988). The duration and frequency of crystalline silica exposure to individual workers is highly variable due to the nature of construction work. Based on conversations with industry professionals (Laird Donaldson, personal communication) it appears that in many cases, cutting, grinding and drilling activities are conducted for relatively short periods several times over the course of a day; However, in some situations workers, especially apprentices, may perform an activity such as cutting for a large portion of the day. The crystalline silica content of construction materials such as stone, brick and concrete is variable, typically ranging from 3.0 percent for hydraulic cement to 21.9 percent for

11 3 crushed and broken sandstone (MSHA, 1997). Consequently, the type and source of the construction material being used can have a considerable effect on crystalline silica exposure. Higher exposures are typically associated with indoor environments where dust is concentrated in a relatively small area and can be re-entrained as a result of other activities (Lofgren, 1993; Riala, 1988). Despite the high crystalline silica exposure potential, the use of dust control measures is not common (Lofgren, 1993). Several exposure assessment studies found construction workers were being exposed to respirable crystalline silica concentrations that exceed regulatory criteria. A Dutch field study examining 29 occupations within the construction industry found that 3.5 % exceeded a respirable crystalline silica exposure level of 0.15 mg/m 3 (Amelsvoort and Tjoe Ny, 1993). Another study conducted in the Netherlands examined the exposure of workers involved in three different work activities at 30 different construction sites (Lumens, 1997). Geometric mean respirable crystalline silica exposures ranged from 0.04 mg/m 3 for inner wall constructors to 1.1 mg/m 3 for demolition workers. An analysis of OSHA inspection data revealed that nonresidential construction workers (SIC 1542) exceeded the OSHA permissible exposure limit (PEL) for respirable crystalline silica by a factor of 15.6 and masonry and other stonework workers (SIC 1741) exceeded the PEL by a factor of 13.0 (Freeman and Grossman, 1995). Extrapolating the OSHA database to a national level, Linch et al (1998) estimated that 2.6 percent of masonry workers (SIC 174), 2.1 percent of heavy construction workers (SIC 162), and 1.3 percent of nonresidential construction workers (SIC 154), 36,000 workers total, are exposed to at least twice the NIOSH recommended exposure limit (0.05 mg/m 3 ) for crystalline silica. The results of construction site monitoring conducted by the Washington State Department of Labor Industries (Lofgren, 1993) also revealed high personal exposure levels, with 93 percent of the measurements being greater than the PEL. These studies strongly suggest that a large number of construction workers are being overexposed to crystalline silica.

12 4 Overall, there are few effective non-engineering controls for reducing crystalline silica exposures during concrete cutting, grinding and drilling activities. Furthermore, available controls for reducing silica dust exposures are not commonly employed at work sites (Lofgren, 1993; Valiante and Rosenman, 1989). Administrative controls can help bring awareness to the issue and foster the use of good practices and other control measures, but alone provide for a small reduction in exposure levels. Substitution of products with lower crystalline silica content is not readily feasible given the prevalence of silica in primary building materials, such as bricks, concrete blocks and poured concrete. Respiratory protective equipment is recommended by NIOSH (NIOSH, 1996) and trade organizations (BCTD, 1996), but require fit testing and proper operation to be effective and may not be worn in many situations. Furthermore, many respirators will not provide effective control if the PEL is exceeded by more than a factor of 10. Ideally, respirators should only be used as an intermittent or supplemental control measure. Given the constraints and limited effectiveness of administrative, process and PPE controls, engineering controls provide the best means of reducing respirable dust and crystalline silica exposures. Engineering controls that are currently available include the application of a water spray or local exhaust ventilation (LEV) at the point of dust generation. The use of water spray systems have been primarily limited to non-portable cut-off saws and larger drilling rigs. Several factors limit the application and use of water spray systems for dust control, including: water source and disposal requirements, potential for water damage inside buildings, surface discoloration, material expansion, cleanup requirements, and cold weather issues (freezing, hypothermia and slip hazards). These constraints are largely eliminated by LEV systems. Although other constraints are associated with LEV systems, such as the need for a vacuum source, reduced visibility of the working surface and a reduction in tool maneuverability, this control alternative appears to be more conducive for use on construction sites.

13 5 Results obtained in previous studies indicate water and LEV systems can effectively reduce dust exposures, but not always to an acceptable level. In a study conducted under controlled conditions, (Hallin, 1983) LEV was found to be most effective for concrete drilling, with crystalline silica exposures observed to be less than 0.1 mg/m 3 for 74 % of the 53 evaluations conducted. The LEV systems used for surface grinding and floor breaking were less effective, with only 26 % of 23 and 7 % of 30 evaluations resulting in crystalline silica exposures less than 0.1 mg/m 3, respectively. The effectiveness of both water and LEV for concrete cutting using a portable saw was evaluated by (Thorpe et al., 1999) under field and laboratory conditions. Respirable dust exposure was typically reduced more than 90 %, with the water and LEV controls being about equally effective. Crystalline silica exposures were less than the limit of detection (LOD), which ranged from 0.2 to 0.6 mg/m 3 (due to the short sampling duration, the elevated LOD limited the ability to determine if control was adequate to reduce exposures below the PEL). In a field evaluation of the use of LEV for tuck point grinding (the removal of mortar between bricks or blocks), Nash and Williams (2000) initially observed a mean crystalline silica exposure reduction of 42 % (n = 2). A substantially higher reduction of 94 % (n = 1) was observed after the LEV system was modified, although the exposure was three times the OSHA PEL. The ventilation rate used for the LEV systems in the above referenced studies was not reported. Despite the commercial availability of LEV systems, few studies have evaluated their effectiveness. Consequently, there is a need for assessing the efficacy of engineering controls for reducing silica exposure under field conditions. The primary objective of this study was to assess the effectiveness of four tools (surface grinder, angle grinder, handheld saw and masonry saw) equipped with commercially available LEV systems for reducing respirable dust and crystalline silica exposure under controlled field conditions.

14 6 MATERIALS AND METHODS Study Location and Description Dust control evaluations were conducted at the Duwamish Branch of South Seattle Community College. The union-sponsored International Masonry Institute (IMI) and Western Washington Cement Masons Training Institute (WWCMTI) both have apprentice training facilities at this location. These two groups provided access to study subjects, materials and equipment, and expertise. Human subjects recruited for the study were apprentices in the IMI or WWCMTI program that had received training for using the tool being evaluated. Each subject had been an apprentice for at least four weeks and had at least two hours experience using the tool being tested. Subject participation was in compliance with procedures approved by the University of Washington human subjects institutional review board. Personal protective equipment used by the study subjects included boots, gloves, earplugs and a powered air purifying respirator. All tools were evaluated in a temporary structure (vinyl tent), which allowed for wind and rain to be controlled while eliminating dust exposure to staff and apprentices working in the vicinity. The tent (Figure 1) had dimensions of 6.1 m (20 feet) wide by 9.1 m (30 feet) long and a volume of m 3 (5,267 ft 3 ). Vinyl walls were erected on three sides of the tent with the northeast facing wall left open. Ventilation through the tent was provided by a 91 cm (36 inch) diameter fan that was placed in a ground level opening on the southwest wall. The fan had a measured flow (hot wire anemometer, 10 point horizontal and vertical traverse) of 111 m 3 /min (3,925 CFM) which resulted in an airflow velocity through the tent of approximately 12.2 m/min (40 feet/min) at the measurement location (Figure 1). Cross sectional airflow measurements taken throughout the tent over several days prior to initiating the study, indicated that airflow through the tent was relatively uniform with the mean velocity ranging from 40 to 60 feet per minute. Smoke tests indicated air currents were drawn by

15 7 the fan through the tent with a minimum of turbulence and swirling. During the study, the airflow velocity through the tent was measured at the beginning, middle and end of each work session using an Alnor hot wire anemometer that was placed 5.2 m (17 feet) upwind of the exhaust fan at a height 1.25 m (49 inches). Experimental Design The study utilized a randomized block design, blocked by subject. Treatments were three levels of exhaust ventilation (0, 30 and 70 CFM) provided to each tools LEV system. Each subject used a single tool over the course of a day. Each of the three treatments was replicated three times in random order for a total of nine 15 minute work sessions per study subject. The initial study design specified two study subjects for each work activity evaluated. This protocol was followed for the surface grinding and paver block cutting work activities. For tuck point grinding five subjects were used to address the high degree of inter subject variability that was observed. A single subject was used to evaluate the hand-held saw and the low ventilation treatment was dropped, as preliminary observations indicated the local exhaust ventilation (LEV) system for this tool was ineffective. During the study, brick cutting was considered to be a potential application for the masonry saw and given the low inter subject variability observed using this saw to cut paver blocks, only one study subject was used for this evaluation. Vacuum Source An industrial vacuum (Dust Control 3700c) was used to provide ventilation airflow for the tools evaluated. The vacuum was equipped with a 24 cm (9.4 inch) diameter cyclone followed by a HEPA filter (99.97 % efficiency). Air was conveyed from the tool to the industrial vacuum through a flexible, 5.2 m (17 feet) long, 5.1 cm (2 inch) diameter corrugated hose. Airflow was adjusted by a valve placed by the investigators on the end of a branch adjacent to the vacuum source. Before and after each assessment, velocity pressure was measured through a 64 cm (25 inch) long, 5.1 cm (2 inch) diameter section of plastic pipe, attached between the industrial vacuum and the hose. Velocity pressure

16 8 measurements, taken across a six-point traverse with a pitot tube (Dwyer) and digital manometer (TSI), were averaged and converted to airflow rate. To counter airflow loss resulting from the increased resistance from dust loading on the HEPA filter, the filter was cleaned five times at evenly spaced intervals during each work session while each tool was being tested. Filter cleaning was facilitated by a built-in system that reversed airflow through the filter, thereby pushing accumulated dust off of the filter. During each cleaning episode, which was approximately 3 to 5 seconds in duration, no airflow was provided to the tool. The industrial vacuum design prevents the release of dust into the working environment during the filter cleaning process. Tools Evaluated and Work Activity Descriptions Prior to initiating the study, a search was conducted to identify hand tools commonly used for tuck point grinding, concrete surface grinding, and block and brick cutting, that were equipped with local exhaust ventilation. The search included a review of internet web sites and correspondence with tool manufacturers, local contractors, and equipment vendors. The masonry and hand-held saws were the only saws identified that were equipped with LEV. Equipment selected for tuck point and surface grinding was recommended by an equipment vendor, and the surface grinder was used by a local contractor. During each work session, observations regarding work practices were recorded. The attributes of the four tools selected for evaluation and the construction materials used for testing them are presented in Table 1 with detailed descriptions provided as follows. Angle Grinder The angle grinder was an electric powered, hand held tool in which the blade is oriented normal to the working surface, thereby allowing the worker to cut a narrow groove of varying depth. The tool is commonly used in a restorative function to remove worn and dilapidated mortar in walls constructed of bricks, blocks, stones or similar building materials. To complete the restoration process, new mortar is placed in the resulting

17 9 groove in a process called tuck pointing. The same tool also may be used to prepare cracks and fissures in concrete floors and walls in a process called crack chasing. The angle grinder was equipped with a shroud (Figure 2) that covered most of the grinding blade, with the portion protruding being equivalent to the grinding depth. For the no ventilation treatment, the front piece of the angle grinder shroud was disconnected, allowing the remaining piece to act as a guard. Tuck point grinding was performed on portable brick walls, constructed by IMI apprentices specifically for the study (Table 1). The Type S mortar used in constructing the walls contained a smaller fraction of cement than the Type M (20 % cement) mortar typically used in more recent masonry construction projects (Randall and Panarese, 1976). However, this composition reflects the type of mortar originally used in constructing the year old buildings that are commonly restored. The lower cement content results in a softer mortar after it has cured. After the walls were constructed, the mortar was allowed to cure for a minimum of four weeks prior to being used. Each individual 15 minute work session was conducted on one third of a wall side. After one side of a wall was used, the wall was turned and work commenced on the opposite side. During each session, study subjects maintained the same orientation to the wall, with the exhaust fan to their right. The wall was aligned lengthwise with the fan (Figure 1). The tool was set to a grinding depth of one cm for all work sessions. At the completion of each work session, the length of mortar joint removed was measured. Surface Grinder The surface grinder was similar in appearance to the angle grinder. However, the grinding cup is positioned parallel to the working surface. This tool is used to produce a smooth finish on poured concrete walls and floors. The surface grinder shroud (Figure 3) covered the grinding cup completely, allowing for a seal between the working surface and the shroud. Air enters the shroud through twenty-two 0.5 cm holes positioned

18 concentrically on the shroud periphery. The shroud was completely removed for the no ventilation treatment. 10 Surface grinding was performed on concrete walls of varying length that are used by the WWCMTI for instructional purposes (Table 1). A 0.88 m 2 (9.5 ft 2 ) area on each wall was marked off for each 15 minute work session. Apprentices were instructed to work for 11.5 minutes on the vertical wall, one minute on the top of the wall (a four inch wide horizontal section), two minutes putting a 45 o chamfer on a vertical side edge and 0.5 minutes putting a 45 o chamfer on a horizontal edge. The latter three exercises were included to mimic real working situations where the seal between the shroud and working surface, and subsequent dust control, is compromised. During each work session, study subjects maintained the same orientation to the wall, with the exhaust fan to their left. The wall was aligned lengthwise with the fan. A piece of plastic sheeting was hung down from the tent ceiling to the top of the wall (3 m) to simulate personal dust exposures associated with a continuous wall. Masonry Saw The gasoline powered masonry saw was specifically designed for cutting paver blocks, 5 10 cm thick, flat blocks of different geometric shape that are used in the construction of walkways, patios, and other similar surfaces. The saw s low profile enables workers to make cuts while in a kneeling position, thus allowing workers to make cuts as they put them in place without changing position. In the study, the saw was raised so that the bottom of the blade was 102 cm (40 inches) from ground level, allowing the worker to operate the saw in a standing position. Cuts are made by pushing the object on a sliding tray into a fixed blade. The saw was equipped with both an LEV and water spray dust control systems. The saw s LEV system is a patented design (U.S. Patent Office, 1999) which consists of a 2.5 cm (1 inch) square tube running the length of the saw immediately below the blade

19 11 (Figure 4). Exhaust ventilation is connected to the open end of the tube, located at the rear of the saw. This arrangement provides for dust capture through a slot near the point of contact between the blade and material being cut. The LEV performs as a push/pull system, with the blade pushing dust into the slot and the exhaust system pulling the dust away. The masonry saw s exhaust ventilation was disconnected and the tube was sealed for the no ventilation treatment. Paver blocks and clay bricks were used to test the masonry saw. During each session, study subjects maintained the same orientation, with the exhaust fan to their back and the saw blade aligned with the exhaust fan. The paver blocks and bricks were stored indoors for a minimum of three weeks to ensure a low moisture content. Approximately nine cuts were made in each block and eight cuts in each brick. The operator was instructed to make two cuts through each of the three holes present in the bricks, as preliminary observations indicated dust control was less effective when cutting across holes. The total number of cuts was recorded to determine a work rate (linear feet cut per hour). Hand-held Saw The gasoline powered hand-held saw s configuration and operation is similar to that of a chain saw, with the engine and controls located near the operator. This tool has numerous applications in the construction industry due to its high power, portability and ability to cut a variety of different materials including metals, concrete, stone and wood. Dust control for the hand-held saw was facilitated by a port (Figure 5) near the back end of the guard to which the exhaust ventilation was connected. The exhaust ventilation was disconnected from the hand-held saw for the no ventilation treatment. Standard C-90 cement blocks were used to test the hand-held saw in a similar manner as to the masonry saw. Blocks being cut were placed on a base so that the top of the block was 80 cm (32 inches) above ground level. Approximately nine cuts were made in each block.

20 12 Exposure Monitoring Dust control effectiveness was assessed by collecting personal and "downstream" respirable dust samples during each work session following NIOSH Method 0600 (NIOSH, 1994). A portable air sampling pump (Gilian) was used to pull air through an MSA nylon cyclone at a rate of 1.7 lpm. Personal exposure samples were taken on each subjects left lapel. The "downstream" sample was collected 107 cm (42 inches) upwind of the exhaust fan. Air sampling trains were calibrated pre- and post-sampling using a primary calibration standard (Gilian). A respirable dust emission rate was calculated by taking the product of the air concentration upwind of the exhaust fan and the building exhaust ventilation rate (Equation 2). ER rd = C rd * Q exhaust (2) Where ER rd is the respirable dust emission rate in g/s, C rd is the respirable dust concentration (mg/m 3 ) and Q exhaust is the tent exhaust ventilation rate (1.853 m 3 /s). This calculation assumes all of the respirable dust released from the cutting or grinding tool remains airborne and exits the tent through the exhaust fan and that the point sample represents the average respirable dust concentration. The respirable dust mass of all samples collected was determined gravimetrically using NIOSH Method 0600 (NIOSH, 1994). Filters were equilibrated in a desiccator for a minimum of 24 hours prior to tare and final weighing. After dust mass was determined, the filters of the three personal samples for a given study test were placed together in a crucible and ashed. The composite samples were subsequently analyzed for quartz and cristobalite by infrared spectrometry using NIOSH Method 7602 (NIOSH, 1994). Laboratory quality was assessed by the collection and analysis of field blanks at a rate of 10%. For quartz analysis, a standard was analyzed twice for every ten samples and

21 variation was found to be less than 5%. Cristobalite levels were all less than the detection limit of 5.5 µg. 13 Data Analysis Air monitoring and experimental conditions data for each day of monitoring were recorded in a series of spreadsheets (Appendices A and B, respectively). Analytical results found to be less than the LOD were entered into the analysis as 50 % of the LOD. The LOD was 5 µg for gravimetric analysis and 5.5 µg for quartz analysis. Linear models were developed with ventilation rate included as a discrete variable. Model development was an iterative process whereby predictors (tool ventilation rate, study subject, interaction of tool ventilation rate and study subject, wind velocity through tent and work rate) were added and their effect on the overall model was considered. Pairwise (a priori) comparisons between treatments were made using t-tests. Effectiveness of the LEV systems for controlling dust was based a comparison of personal respirable dust and quartz exposures to the OSHA 8-hour TWA-PEL and reduction in respirable dust exposure (Equation 3): % Reduction = [(NV gm V gm )/NV gm ] * 100 (3) Where NV gm is the geometric mean respirable dust exposure for a study subject under the no ventilation treatment and V gm is the geometric mean respirable dust exposure for a study subject under ventilation treatment.

22 TABLE 1. Attributes of Tools and Construction Materials Used in Study Tool Work Activity Attribute Tuck Point Grinding Surface Grinding Block and Brick Cutting Block Cutting Tool Angle Grinder Flat Grinder Masonry Saw Hand-held Saw Make Flex (Porter Cable) Flex (Porter Cable) EDCO Partner Model F1509 FR LD 1509 FR GMS-10 K650 Active Power Source Electric Electric Gasoline Gasoline Weight 4.1 kg (9.1 lbs) 2.9 kg (6.4 lbs) 53 kg (116 lbs) 9.4 kg (20.7 lbs) Dimensions A 37 x 18 x 18 cm 15 x 7 x 7 in 36 x 11 x 18 cm 14 x 5 x 7 in 104 x 64 x 48 cm 41 x 25 x 19 in 76 x 30 x 30 cm 25 x 10 x 10 in Power (watts) 1,200 1,200 3,000 Operating RPMs 10,000 10,000 5,500 3,600 Blade Type Diamond Diamond cup Diamond, dry cut Diamond Make Concut Dimas EDCO Diameter (cm) Tip speed (ft/min) 3,750 4,430 2,830 5,500 Ventilation Shroud Face dimensions (cm) 12.3 x 4.0 b 17.8 C 17.5 x 0.8 B 38.1 x Face area (cm 2 ) Capture velocity (ft/min) 555 / 1,401 D 110 / 277 1,971 / 4, / 570 Construction Material Brick Walls with Type S mortar: 70 % sand 20 % sand Concrete Walls Paver blocks Bricks with three 3.8 cm (1-1/2 in) holes Concrete blocks(c-90) Dimensions (length x height x width) 10 % hydrated lime 1.8 x 1.4 x 0.15 m 6.0 x 4.6 x 0.5 ft 1 cm wide mortar joints variable length 1.2 x 0.10 m 4.0 x 0.33 ft Paver blocks: 29.5 x 29.5 x 5.7 cm 11-5/8 x 11-5/8 x 2-1/4 in Bricks: 19.4 x 6.4 x 9.4 cm 7-5/8 x 2-1/2 x 3-11/16 in x 20.3 x 20.3 cm 12 x 8 x 8 in A Length by height by width B Length by width C Diameter D Face velocity at ventilation ariflow rates of 29.4 and 74.2 CFM, respectively (overall average ventilation rate for low and high treatments)

23 15 5 ft 12 ft Continuous velocity monitor x Fan 6 ft Tool exhaust measurement 20 ft Vacuum source - aircleaner 30 ft

24 FIGURE 2: Angle Grinder 16

25 FIGURE 3: Surface Grinder 17

26 FIGURE 4: Masonry Saw 18

27 FIGURE 5: Hand-held Saw 19

28 RESULTS 20 Experimental Conditions Wind velocity across the work area, ventilation airflow rate, work rate and respirable crystalline silica content of the construction materials were measured during the study to assess potential confounding effects on personal dust exposure. These data are presented in Appendices C-1 through C-5. Wind velocity through the tent was normally distributed with an overall mean of 11.5 m/min (n = 91, SD = 3.7). Linear models indicated that wind velocity wasn't a significant predictor of personal respirable dust exposure or emission rate and was not included in final linear models. Relatively precise control of LEV rate was achieved. The overall mean (±SD) for the low (29.4 ±1.5) and high (74.2 ±5.2) ventilation treatments did not vary considerably from the target of 30 and 75 CFM, respectively. Plots of personal respirable dust exposure versus ventilation rate (Figures 6, 7, 8) indicate that slight changes in ventilation rate did not affect personal exposure levels. Ventilation rate was accordingly used as a discrete variable in linear model development. The overall pre- and post-work session ventilation rate measurements were in reasonable agreement, with the overall mean post-work session ventilation rate being slightly greater (1.6% ±7.4) than the overall pre-work session ventilation rate. This difference is within the experimental error that would be expected for this type of measurement. The work rate was determined for all work activities except surface grinding. For surface grinding, an accurate means of measuring the depth of surface removed was not available. The mean (±SD) overall work rates, in linear feet cut/hour, were tuck point grinding: (±41.9); concrete block cutting: (±16.5); paver block cutting: 79.3 (±12.5); and brick cutting: 86.4 (±14.9). The number of work rate measurements taken for each work activity is equal to the "n" presented in Table 2. Although a higher work rate would increase the rate of dust generation, linear model analysis indicated that the inclusion of work rate wasn't a significant predictor of personal respirable dust exposure or emission

29 21 rate and was subsequently not included in linear models. The percent respirable quartz content of each of the five different materials used ranged from 15 to 24 % and did not vary appreciably (coefficient of variation < 20 %). Personal Dust Exposure Results Personal respirable dust measurements were used to assess the effectiveness of the LEV systems tested for reducing worker exposure during specific work activities (Table 2). Since the exposure data were approximately log normally distributed they were log transformed prior to analysis. For the hand-held saw, personal respirable dust exposure for the high ventilation rate treatment (GM = 2.44 mg/m 3 ) was the same as the no ventilation treatment (GM = 2.35 mg/m 3 ). The other three LEV equipped tools (angle grinder, surface grinder and masonry saw) significantly reduced personal respirable dust exposure for both the low and high ventilation rates tested as compared to the no ventilation treatment (p<0.05). For these three tools, the mean exposure level for the high ventilation rate treatment was also less than that of the low ventilation rate. However, differences between these two treatments were significant for tuck point grinding (p<0.1) and paver block cutting (p<0.01). Overall, similar results were observed for each subject considered individually, with the notable exception of tuck point grinding. For this work activity, Subjects 3 and 5 s exposure levels, at both the high and low ventilation treatments, were significantly different (p<0.10) from that of the no ventilation treatment. In contrast, subject 1's exposure at the high ventilation rate treatment was not significantly different (p>0.05) from the no ventilation treatment and subjects 2 and 5 s, exposure levels at both the low and high ventilation treatments were not significantly different (p>0.05) from that of the no ventilation treatment. Considerable inter subject variability was noted for tuck point grinding, compared to the other work activities (Figures 6, 7, 8). The greater variability associated with this work activity may have been the result of differences in study subject work technique.

30 22 Linear models were developed for each work activity using the log of personal dust exposure as the dependent variable. The independent variables included in the model were ventilation rate as a discrete variable (coded as no, low and high ventilation) and subject. The interaction of subject and ventilation rate, as well as wind velocity and workrate, had no effect on the model and were subsequently not included. The linear model results are presented in Table 3. The resulting r 2 values indicate that ventilation rate and subject are good predictors of personal respirable dust exposure, with the exception of block cutting. Respirable Dust Emission Rate Respirable dust emission rate data were used to assess the effectiveness of the LEV systems tested for reducing area dust concentrations during specific work activities and represent the total amount of dust escaping from the tool (Table 4). These data were also noted to be approximately log normally distributed and were log transformed prior to analysis. The hand-held saw LEV produced a small non-significant (p>0.05) decline in the respirable dust emission rate. A significant (p<0.05) reduction in emission rate was observed for the other three LEV equipped tools. For these three tools, the high ventilation rate treatment resulted in a lower, but non-significant, emission rate as compared to the low ventilation rate treatment. Linear models were developed for each work activity using (log) emission rate as the dependent variable. The model development process and outcome were similar to that of the personal exposure linear model, with subject and ventilation being included as independent variables. The model results (Table 5) support the importance of ventilation rate as a predictor of respirable dust emission rate.

31 23 The relationship of personal exposure (log transformed) and emission rate (log transformed) is demonstrated in Figures A high level of association was observed between these two exposure measurement variables. Exposure Reduction and Comparison to PELs Table 6 shows the reduction in respirable dust personal exposure levels resulting from the use of LEV and a comparison of the mean exposure levels to the OSHA Permissible Exposure Levels (PELs). With the exception of the hand-held saw, LEV resulted in a considerable reduction in personal respirable dust exposure levels as compared to the no ventilation treatment. Despite the very large reduction in concentration (70-90% at the low ventilation rate and 80-95% reduction at the high ventilation rate), personal respirable dust exposures remained very high ( x PEL at the low ventilation rate and 0.5 to 1.5 x PEL at the high ventilation rate). Comparison of the study results to the OSHA 8 hour TWA-PEL assumes the concentrations observed during the 15 minute work sessions would be maintained for an eight hour period. Without LEV, personal respirable dust exposures ranged from 0.5 to 34 times the PEL. Interestingly, the lowest exposure was associated with the hand-held saw the only tool for which LEV was not effective. This is a result of the saw conveying generated dust away from the operator, an observation which is supported by the very high emission rate for this tool (Table 4). At the high ventilation rate, LEV was effective at reducing respirable dust exposure levels below the PEL for tuck point grinding, and paver block and brick cutting. Surface grinding achieved the highest overall reduction in dust exposure levels, but still exceeded the respirable dust PEL by a factor of 1.66 at the high ventilation rate treatment. Personal exposure levels of respirable crystalline silica and a comparison of the levels to the OSHA PELs are presented in Table 7. Silica exposure levels associated with the no ventilation treatment are remarkably high, ranging from 4.4 to almost 360 times the PEL.

32 24 As per the respirable dust exposure, the application of LEV reduces the exposure considerably. However, even at the high ventilation rate, the respirable quartz PEL is exceeded by a factor of 5 to 20 for all tools.

33 25 TABLE 2. Personal Respirable Dust Exposure Levels (mg/m 3 ) Study No Ventilation Low Ventilation High Ventilation Low v. High B Work Activity Subject GM (GSD) A GM (GSD) GM (GSD) Comparison Tuck point grinding (n = 14) (n = 14) (n = 13) All (2.42) 6.11 (1.85)*** C 3.01 (3.31)*** D * (1.10) 6.70 (1.41)*** 3.06 (8.19) (1.90) 3.56 (2.38) 3.56 (2.19) (1.06) 9.93 (1.20)*** 4.29 (2.22)*** (1.57) 8.55 (1.32)** 3.53 (1.99)* (2.10) E 3.50 (1.90) E 0.37 F Surface grinding (n = 5) (n = 6) (n = 5) All (1.24) (1.72)*** 8.00 (1.35)*** (1.13) (2.32)*** 8.66 (1.34)*** (1.35) E (1.10)*** 7.11 E (1.44)** * Paver block cutting (masonry saw) (n = 6) (n = 6) (n = 6) All (1.42) (1.44)*** 4.31 (1.48)*** *** (1.22) (1.23)*** 4.96 (1.65)*** ** (1.38) (1.70)*** 3.74 (1.32)*** ** Brick cutting (masonry saw) (1.64) 7.27 (1.18)** 3.67 (2.02)** Block cutting (hand-held saw) (1.63) 2.44 (1.58) A Geometric mean and geometric standard deviation B Comparison (t-test) of low and high ventilation rates C Comparison (t-test) of low ventilation to no ventilation D Comparison (t-test) of high ventilation to no ventilation * p<0.10 ** p<0.05 *** p<0.01 n = 3 per study subject treatment unless noted: E N = 2, F N = 1

34 Personal Respirable Dust Exposure (mg/m 3 ) Subject 1 Subject 2 Subject 3 Subject 4 Subject Ventilation Airflow Rate (CFM) FIGURE 6. Personal respirable dust exposures (mg/m 3 ) resulting from tuck point grinding work activity as a function of ventilation airflow rate

35 Personal Respirable Dust Exposure (mg/m 3 ) Subject 1 Subject Ventilation Airflow Rate (CFM) FIGURE 7. Personal respirable dust exposures (mg/m 3 ) resulting from surface grinding work activity as a function of ventilation airflow rate

36 Personal Respirable Dust Exposure (mg/m 3 ) Subject 1 (paver blocks) Subject 2 (paver blocks) Subject 1 (bricks) Ventilation Airflow Rate (CFM) FIGURE 8. Personal respirable dust exposures (mg/m 3 ) resulting from paver block and brick cutting work activities as a function of ventilation airflow rate

37 Personal Respirable Dust Exposure (mg/m 3 ) 10 Subject 1 Subject 2 Subject 3 Subject 4 Subject Respirable Dust Mass Emission Rate (mg/s) FIGURE 9. Personal respirable dust exposures (mg/m 3 ) vs. respirable dust emission rate (mg/s) for tuck point grinding work activity (r 2 = 0.488).

38 30 TABLE 3. Linear Models [β (SE)] Describing Log Respirable Dust (mg/m 3 ) Exposure Levels Variable Tuck Point Grinding Surface Grinding Paver Block Cutting (Masonry Saw) Brick Cutting (Masonry Saw) Block Cutting (Hand-held Saw) n Subjects Intercept 2.24 (0.40)** 5.07 (0.22)** 4.54 (0.18)** 3.28 (0.29) ** 0.85 (0.27)* Ventilation Rate A Low Airflow (0.31)** (0.26)** (0.22)** (0.41)** High Airflow (0.31)** (0.25)** (0.22)** (0.41)** 0.04 (0.39) Subject B (0.45)* 0.06 (0.21) (0.18) (0.45) (0.45)** (0.45)* Model r A Reference: no ventilation provided B Reference: N th subject where N = total number of subjects * p<0.05 ** p<0.01

39 31 TABLE 4. Respirable Dust Emission Rate (mg/s) Work Study No Ventilation Low Ventilation High Ventilation Activity Subject GM (GSD) A GM (GSD) GM (GSD) Tuck point grinding (n = 13) (n = 14) (n = 13) All (1.76) 0.96 (3.28)*** B 0.50 (4.16)*** C (1.49) 2.47 (1.29)*** 0.42 (7.15)** (1.34) 0.90 (4.77)** 0.25 (1.66)*** (1.29) 0.80 (3.66)*** 0.58 (7.18)** (1.17) D 0.89 (4.39)* 1.33 (3.66)* (2.39) D 0.37 (2.62)** D 0.24 (1.00) E Surface grinding (n = 6) (n = 6) (n = 6) All (1.19) 4.38 (2.32)*** 3.06 (2.02)*** (1.15) 6.34 (2.99)** 3.93 (1.36)*** (1.15) 3.02 (1.47)*** 2.38 (2.66)*** Paver block cutting (masonry saw) (n = 6) (n = 6) (n = 6) All (1.20) 2.79 (1.35)*** 2.45 (1.97)*** (1.05) 3.34 (1.28)*** 2.41 (1.95)*** (1.31) 2.33 (1.30)*** 2.49 (2.33)** Brick cutting (masonry saw) (1.52) 0.64 (2.55)** 1.14 (4.93) Block cutting (hand-held saw) (1.36) (1.54) Emission Rate (mg/s) = Concentration (mg/m 3 ) * Tent Ventilation Rate (1.853 m 3 /s) A Geometric mean and geometric standard deviation B Comparison of low ventilation to no ventilation C Comparison of high ventilation to no ventilation * p<0.10 ** p<0.05 *** p<0.01 N = 3 per study subject - treatment unless noted: D N = 2, E N = 1

40 32 TABLE 5. Linear Models [β (SE)] Describing Log Respirable Dust Emission Rate (mg/s) Tuck Point Grinding Surface Grinding Paver Block Cutting (Masonry Saw) Brick Cutting (Masonry Saw) Block Cutting (Portable Saw) n Subjects Intercept 2.59 (0.55)** 4.21 (0.30)** 3.00 (0.22)** 2.08 (0.63) 4.67 (0.22)** Ventilation Rate A Low Airflow (0.43)** (0.37)** (0.26)** (0.89)* High Airflow (0.44)** (0.37)** (0.26)** (0.89) (0.30) Subject B (0.62) 0.34 (0.30) 0.01 (0.22) (0.62) (0.62) (0.62) Model r A Reference: no ventilation provided B Reference: N th subject where N = total number of subjects * p<0.05 ** p<0.01

41 Personal Respirable Dust Exposure (mg/m 3 ) Subject 1 Subject Respirable Dust Mass Emission Rate (mg/s) FIGURE 10. Personal respirable dust exposures (mg/m 3 ) vs. respirable dust emission rate (mg/s) for surface grinding work activity (r 2 = 0.718).

42 Personal Respirable Dust Exposure (mg/m 3 ) Subject 1 (paver blocks) Subject 2 (paver blocks) Subject 1 (bricks) Respirable Dust Mass Emission Rate (mg/s) FIGURE 11. Personal respirable dust exposures (mg/m 3 ) vs. respirable dust emission rate (mg/s) for paver block and brick cutting work activities (Blocks: r 2 = 0.748; Bricks: r 2 = 0.488).

43 TABLE 6. Comparison of Personal Dust Exposure Levels to PEL and Reduction from LEV No Ventilation Low Ventilation Rate High Ventilation Rate Work Times PEL A % Reduction Times PEL % Reduction Times PEL Activity k Mean (SD) Mean (SD) Mean (SD) Mean (SD) Mean (SD) Tuck point grinding (3.7) 70.0 (14.6) 1.4 (0.7) 82.8 (20.8) 1.0 (0.8) Surface grinding (6.5) 93.0 (2.1) 2.5 (1.0) 95.2 (0.1) 1.7 (0.5) Paver block cutting (masonry saw) (7.3) 85.1 (4.4) 2.8 (1.0) 94.9 (2.6) 0.9 (0.4) Brick cutting (masonry saw) (2.4) (0.2) (0.5) Block cutting (hand-held saw) (0.2) (0.3) k = number of subjects, n = 3 for each subject with exceptions noted in Table 2 PEL based on 8 hr exposure A Times PEL = arithmetic mean (study subjects) exposure concentration/osha 8-hour TWA-PEL 35