T. Ogansanya, P. Greenley, K. Ahn, L. DiBerardinis, Massachusetts Institute of Technology, Cambridge, MA; H. Palacios-Fernandea, Harvard University, Cambridge, MA.
The effect of training on chemical fume hood work practices will be presented for two MIT buildings where low flow fume hoods were installed. MIT’s chemistry building was renovated in 2001. One of the goals of the renovation was to increase the amount of fume hood space for each graduate student. For project budget reasons, the larger fume hoods had to be accommodated with very little increase in supply air to the building. This resulted in hoods with combination sashes being installed along with a reduced design opening vertical sash height. A survey was conducted in the summer of 2005 to evaluate hood sash use with regard to safety and energy conservation. It was observed that hoods were used only in the horizontal sash mode and were not closed when not being used. Training of fume hood users was conducted to see if hood use practices could be changed for increased safety and energy conservation purposes. Hood work practices before and after training will be presented. The Brain and Cognitive Sciences Building was opened in September of 2005. The research being conducted and the fume hood controls design is very different from the Chemistry Building. The setup of the constant volume, vertical sash, snf low flow fume hoods will be described. Training and monitoring of fume hood use will be conducted and reported on for this presentation.
R. Valladares, W. Sieber, J. Kratzer, CDC/NIOSH, Cincinnati, OH.
Respirable crystalline silica dust exposure in residential roofers is a recently recognized hazard resulting from cutting concrete roofing tiles. Roofers who cut tiles using masonry saws, can be exposed to high concentrations of respirable dust. Silica exposures remain a serious threat to nearly 2 million U.S. workers. Although it is well established that respiratory diseases associated with exposure to silica dust are preventable, they continue to occur and cause disability or death. The effectiveness of a commercially available local exhaust ventilation (LEV) system and a water suppression system to reduce silica exposures were evaluated separately. The LEV system exhausted 500 cubic feet per minute, while the water suppression system supplied 2 gallons per minute to the saw blade. Using a randomized block design, implemented under laboratory conditions, three trials were conducted (no control, water control, and ventilation control) on two types of concrete roofing tiles using the same saw. Each treatment was replicated for a total of eight 30-sec runs per treatment per tile. Analysis of variance was performed using mean concentration levels from each run and control. The use of water controls and ventilation controls resulted in a statistically significant (p < 0.05) reduction of mean respirable dust concentrations for each tile. Mean concentrations using the water control were statistically significantly less than that of the ventilation control. The percent reduction for respirable dust concentrations was 99% for the water control and 91% for the LEV. Water is a good method for reducing crystalline silica exposures. However, water source and disposal requirements, water damage potential, surface discolorations, material expansion, cleanup, and other requirements make use of water in many situations problematic. LEV may be more desirable, but designing a system with a sufficient capture velocity that will control silica concentrations below occupational criteria might be difficult.
B. Altemose, Johnson & Johnson, Somerville, NJ.
Isoflurane is a halogenated anesthetic agent commonly used during veterinary surgeries. Successful application of local exhaust ventilation reduced occupational exposures to isoflurane in veterinary applications where traditional waste anesthetic gas scavenging was inadequate. Adjustable local exhaust ventilation arms were installed at four surgical tables. In addition, exhaust ventilation was installed to exhaust 70% of the air circulating in a biosafety cabinet, which previously operated with recirculation only. Although 100% exhaust would have been preferred, that would have required a new biosafety cabinet, and mathematical modeling indicated the 70% exhaust option would achieve the desired results. The three tasks of greatest concern for exposure prior to installation of the ventilation arms were: (1) surgery on large animals anesthetized via a mask, (2) surgery on small animals inside the recirculating biosafety cabinet, and (3) surgery prep for large animals. Exposures during surgery on large animals anesthetized via a mask were reduced from a geometric mean of 2.7 ppm (maximum concentration 5.0 ppm) to 0.19 ppm (maximum concentration less than 0.34 ppm, the limit of detection). At the biosafety cabinet, exposures were reduced from 17 ppm (maximum concentration 20 ppm) to 0.27 ppm (maximum concentration 0.94 ppm). Exposures during surgery prep for large animals were not significantly reduced. Two causes were identified: the local exhaust ventilation in this area was not properly balanced, and the nature of large animal surgery prep made it difficult to position the arm close to the anesthesia mask. It is believed that increased ventilation, proper positioning of the ventilation arm, and other work practice modifications will allow for exposures to be maintained below 1.0 ppm.
J. Sheehy, A. Echt, A. Garcia, CDC/NIOSH, Cincinnati, OH.
A series of recent NIOSH Health Hazard Evaluations has highlighted a newly recognized hazard associated with the use of concrete tiles in the residential roofing industry. Roofers cutting these tiles with tools such as gasoline-powered saws are exposed to high concentrations of respirable dust, crystalline silica, and noise. Silicosis is an irreversible, progressive, respiratory disease caused by inhaling respirable crystalline silica dust. The hazardous nature of working on pitched roofs makes it difficult to use traditional engineering control solutions. The use of concrete tiles is growing, especially in the western states impacting thousands of construction workers. The primary focus of this study is to evaluate and document engineering controls effective in reducing respirable dust and silica exposures during tasks where roofers cut concrete tiles. The suite of silica and dust control options investigated in this project includes the use of hand-held tools with local exhaust ventilation, wet methods with the application of water while cutting, and mechanical tile cutters. Effective controls are those that maintain exposures below occupational exposure limits, NIOSH REL and OSHA PEL, or those that reduce exposure above 70% when controls are used. NIOSH researchers conducted demonstration and evaluation surveys at roofing tile training facilities and at a number of homes where concrete roofing tiles were installed. Area and personal respirable dust samples were collected and analyzed following NIOSH Method 600 and crystalline silica according to NIOSH Method 7500. Results from the surveys showed that worker exposures to respirable dust while using powered saws with local exhaust ventilation approach occupational exposure limits. Wet methods have numerous problems including staining of tiles. However, mechanical tile cutters produced very low levels of dust and silica. In conclusion, it appears that engineering control methods are available that maintain respirable dust and silica controls well below occupational exposure limits.
S. Guffey, W. El-Nahas, West Virginia University, Morgantown, WV.
Ethanol concentrations were measured on an anthropometrically correct, heated, breathing manikin holding a source in its hands at waist height while both sitting and standing in a wind tunnel with its back to the cross draft. Sampling probes were placed at the manikin’s mouth, nose, forehead, neck, both collars, center chest, and both lapels. Test conditions included five levels of cross-draft velocities (11, 27, 48, 82, and 104 ft/min), two levels of body heat (unheated/heated), and two levels of posture (sitting/standing). Wind tunnel velocity, heating, and posture each had a statistically significant effect for all sampling locations. For the unheated manikin, concentrations for all sampling locations declined monotonically with wind tunnel velocity. However, for the heated conditions, concentrations varied with an inverted-V relationship with wind tunnel velocity. For heated conditions, concentrations at the mouth were always higher for standing than sitting. Concentrations measured at the chest and shoulder levels were higher than mouth concentrations for the standing posture and were lower than mouth concentrations for sitting. Concentrations measured at the forehead location were always lower than concentrations measured at the mouth for both sitting and standing. Based on the results of this study, center chest, left and right lapels, neck, left and right collars, and forehead locations were unreliable surrogates for actual inhalation exposure. Surprisingly, adjacent to the nose also was not always a reliable surrogate, either. The lapels and collars were generally very poor surrogates for mouth concentrations. The dramatic effects of heating and postures suggest that manikins used to represent humans in exposure studies should always be heated and always tested in both sitting and standing postures.
S. Guffey, W. El-Nahas, West Virginia University, Morgantown, WV.
In a continuation to a previous study, ethanol concentrations were measured on an anthropometrically correct, heated, breathing manikin holding a source in its hands at waist height while both sitting and standing in a wind tunnel with its back to the cross draft. Sampling probes were placed at the manikin’s mouth, nose, forehead, neck, both collars, center chest and both lapels. Test conditions included Breathing (breathing/no breathing), two levels of hairstyle (wig/no wig), five levels of cross-draft velocities (11, 27, 48, 82, and 104 ft/min), and two levels of posture (sitting/standing). The substantial effects of velocity and posture were consistent with an earlier study whether breathing and the wig were included or not. Concentrations varied with an inverted-V relationship with wind tunnel velocity. Likewise, concentrations at the mouth were always higher for standing than sitting. Concentrations measured at the chest and shoulder levels were higher than mouth concentrations for standing posture and were lower than mouth concentrations for sitting. Concentrations measured at the forehead location were always lower than concentrations measured at the mouth for both sitting and standing. Wind tunnel velocity, breathing, and posture each had statistically significant effects on concentrations for all sampling locations. The effect of the wig on inhaled concentrations was significant for both sitting and standing postures. Based on this study, exposure studies using manikins as surrogates should include different hair lengths and postures. Manikins should have simulated natural breathing.
S. Guffey, A. El-Sotouhy, West Virginia University, Morgantown, WV.
Ethanol concentrations were measured on five human subjects, all with a source in a 9-inch covered pie pan at waist height and within easy reach. Subjects moved blocks across the top of the source to the other side and back again. Subjects “worked” sitting or standing in a wind tunnel with their backs to the cross draft. Sampling probes were placed at each subject’s forehead, adjacent to the nose (“nose”), mouth, neck, left and right collars, center chest, and right and left lapels. Test conditions included cross-draft velocities of 11, 27, 48, and 103 ft/min, breathing/not breathing, and sitting/standing. Effects of not breathing were simulated by having the subject breathe through a long tube. Concentrations varied with wind tunnel velocity (p< 0.01) in an inverted V-shape and were roughly twice as high for sitting as standing. Sitting/standing was significantly related to concentrations at all locations (p<0.01). Breathing through a tube appeared to reduce the concentrations at most sampling sites but was not significant. Concentrations at the forehead averaged 90% of the nose with 90% of values between 75% and 104%. All other locations were higher than the nose, with center chest averaging 180% of the nose. The ratio of lapels to the nose varied greatly with sitting/standing (120% and 170%, respectively) and frequently exceeded 200%. The corresponding values for the collars were 100% (sitting), 116% (standing), and 141% for the 95 percentile value. The concentrations at the neck averaged 112% of the nose but ranged from 60% to 160%. The dramatic effects of velocities and postures suggest that exposure studies should consider multiple postures and cross-draft velocities. The lapels and chest samples were poor surrogates for the nose, but the forehead modestly underestimated and the collars modestly overestimated concentrations at the nose.
J. Dessagne, R. Regnier, INRS, Vandoeuvre, France.
Most open ventilated booths frequently used to controlling pollution in workshops employ a horizontal airflow introduced on one side open to the workshop and extracted on the opposite side. Vertical airflow ventilation is an alternative that could improve pollutant exposure of the operator. Building constraints have led manufacturers to offer an intermediate solution in which the main airflow is not vertical, but directed obliquely. An experimental study has been carried out by INRS in the stonecutting sector on three cabins, one horizontal, two vertical, and two “oblique” airflow units. Measurements of dust concentration in the breathing area were performed under controlled working configurations close to those encountered in this field. The study showed the superiority of vertical airflow over horizontal airflow in many configurations in a ratio of between 20 to 200. On average, vertical airflow was more efficient than oblique airflow in a large number of tested situations. The two oblique airflow cabins gave different results. In some situations, one cabin’s performance characteristics approached those of vertical airflow cabins, whereas the other gave very scattered results, reflecting efficiencies lower than those of the other two cabins in many situations. For standard stonecutting operations (cutting, grinding), oblique airflow was more sensitive to position and stonecutters’ machining method than vertical airflow. Due to the interaction of many parameters (type of stone, moisture content, type of operation, position of operator), a modeling derived from a scoring method was used to analyse the results and to lead to guidelines for choice of the appropriate solution in given conditions.
G. Knutson, Knutson Ventilation, Inc., Edina, MN.
ANSI/ASHRAE Standard 110 “Method of Testing Performance of Fume Hoods” has been used to evaluate the performance of laboratory hoods (fume hoods) for over 20 years. The recent revision to the standard includes tools that can be used to investigate the variables that influence the performance of a laboratory hood. A new appendix addresses the diagnostic application of the standard in investigating the performance of laboratory hoods. Some apparent causes of poor performance can be attributed to leakage of tracer gas from sources other than through the face of the hood. More frequently, poor performance can be associated with specific causes that can be investigated. Finally, some techniques address the robustness of the laboratory hood.
Posted May 30, 2006