HHS Public Access Author manuscript Author Manuscript Author ManuscriptJ Occup Author Manuscript Environ Hyg. Author Author Manuscript manuscript; available in PMC 2015 August 17. Published in final edited form as: J Occup Environ Hyg. 2014 ; 11(10): D164–D173. doi:10.1080/15459624.2014.933959. EVALUATION OF LEAKAGE FROM FUME HOODS USING TRACER GAS, TRACER NANOPARTICLES AND NANOPOWDER HANDLING TEST METHODOLOGIES Kevin H. Dunn1,*, Candace Su-Jung Tsai2, Susan R. Woskie3, James S. Bennett1, Alberto Garcia1, and Michael J. Ellenbecker3 1Engineering and Physical Hazards Branch, Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, OH 2School of Health Sciences, Purdue University, West Lafayette, IN 3Department of Work Environment, College of Health Sciences, University of Massachusetts Lowell, Lowell, MA Abstract The most commonly reported control used to minimize workplace exposures to nanomaterials is the chemical fume hood. Studies have shown, however, that significant releases of nanoparticles can occur when materials are handled inside fume hoods. This study evaluated the performance of a new commercially available nano fume hood using three different test protocols. Tracer gas, tracer nanoparticle, and nanopowder handling protocols were used to evaluate the hood. A static test procedure using tracer gas (sulfur hexafluoride) and nanoparticles as well as an active test using an operator handling nanoalumina were conducted. A commercially available particle generator was used to produce sodium chloride tracer nanoparticles. Containment effectiveness was evaluated by sampling both in the breathing zone (BZ) of a mannequin and operator as well as across the hood opening. These containment tests were conducted across a range of hood face velocities (60, 80, and 100 feet/minute) and with the room ventilation system turned off and on. For the tracer gas and tracer nanoparticle tests, leakage was much more prominent on the left side of the hood (closest to the room supply air diffuser) although some leakage was noted on the right side and in the BZ sample locations. During the tracer gas and tracer nanoparticle tests, leakage was primarily noted when the room air conditioner was on for both the low and medium hood exhaust air flows. When the room air conditioner was turned off, the static tracer gas tests showed good containment across most test conditions. The tracer gas and nanoparticle test results were well correlated showing hood leakage under the same conditions and at the same sample locations. The impact of a room air conditioner was demonstrated with containment being adversely impacted during the use of room air ventilation. The tracer nanoparticle approach is a simple method requiring minimal setup and instrumentation. However, the method requires the reduction in background concentrations to allow for increased sensitivity. *indicates the corresponding author with, [email protected]. Disclaimer: Mention of a specific product or company does not constitute endorsement by the Centers for Disease Control and Prevention. The findings and conclusions in this manuscript are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Dunn et al. Page 2 Author ManuscriptKeywords Author Manuscript Author Manuscript Author Manuscript nanoparticle; fume hood; containment; tracer gas INTRODUCTION Occupational health risks associated with manufacturing and the use of nanomaterials are not yet clearly understood. However, initial toxicological data indicate that there is reason for caution. Pulmonary inflammation has been observed in animals exposed to titanium (1-3) dioxide (TiO2) and carbon. Other studies have shown that nanoparticles can translocate to the circulatory system and to the brain and cause oxidative stress.(4, 5) Perhaps the most troubling finding is that carbon nanotubes can elicit asbestos-like responses in mice.(6, 7) In light of these results, it is important for producers and users of engineered nanomaterials to reduce employee exposure and manage risks appropriately. A survey was conducted of producers and users of engineered carbonaceous nanomaterials (ECNs) in the U.S. at a research and development or pilot scale plant with plans to scale up within 5 years.(8) All participating companies reported using some sort of engineering control to reduce worker exposure to ECN. The most commonly reported control used to minimize workplace exposures to ECN was the chemical fume hood. Recent research has shown that the fume hood may allow releases of nanomaterials during their handling and manipulation.(9) This research evaluated exposures related to the handling (i.e., scooping and pouring) of powder nanoalumina and nanosilver in a constant air volume (CAV) hood, a bypass hood, and a variable air volume (VAV) hood. The study showed that the conventional fume hood in which face velocity varies inversely with sash height allowed the release of significant amounts of nanoparticles during pouring and transferring activities involving nanoalumina. New lower flow hoods adapted from pharmaceutical powder handling enclosures are being marketed and used for the manipulation of nanomaterials. The use of lower flows may reduce the impact of turbulence and the body wake on the potential for fume hood leakage. However, there is little information on their performance in the scientific literature. A common method used to evaluate performance of fume hoods is the quantitative tracer gas test. These tests are sometimes conducted with a mannequin in front of the hood to simulate the effect of the user on the air patterns surrounding the face of the hood. For these tests, a tracer gas (typically sulfur hexafluoride, SF6) is released inside the hood using a dispersion device. The performance of the hood is evaluated by measuring the tracer gas concentration at the breathing zone (BZ) of the mannequin or at the hood opening. Tseng et al. evaluated the results of British, European and American protocols for tracer gas fume hood testing using a traditional laboratory fume hood. This testing showed that airflow patterns and the performance of the hood are integrally related.(10) The choice of source position, hood design and presence of a mannequin are important to a careful evaluation of the fume hood. The American Society of Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) standard evaluates fume hood performance based on the traditional industrial hygiene precept of evaluating operator breathing zone exposure.(11) Tseng et al. J Occup Environ Hyg. Author manuscript; available in PMC 2015 August 17. Dunn et al. Page 3 found, however, that this method failed to detect serious leakages which may not be Author Manuscript Author Manuscript Author Manuscript Author Manuscript acceptable for hazardous materials. The British standard suffered from a measurement method which averages the spatial variability and dampened the effect of local leaks by combining sample flows from all locations across the hood face. New test methods need to be developed and evaluated. Most laboratory fume hood test protocols used today are based on utilizing SF6. SF6, however, has been identified as a strong greenhouse gas with a global warming potential 23,900 times greater than carbon (12) dioxide. The state of California has prohibited the sale and use of SF6 for a broad range of applications and allowed the use for one-time testing of fume hoods “for the purpose of reducing laboratory fume hood face velocity when the hood is unattended and realizing the associated energy savings”.(13) ASHRAE Technical Committee TC 9.10, Laboratory Ventilation, has recommended research to investigate potential replacement tracers critical for verification of laboratory fume hood devices. This study evaluated the performance of a new nano fume hood across three different hood exhaust air flows using three different test protocols. For the testing, tracer gas, tracer nanoparticle and nanopowder handling protocols were used to evaluate the hood. A static test procedure using tracer gas and nanoparticles and an active test using an operator handling nanoalumina were conducted. Samplers were placed in the operator breathing zone as well as at the left and right corner of the hood to assess leakage from the hood at areas known to have high turbulence. These containment tests were conducted with the room ventilation system turned off and again with the system on. The results of the three test methods are compared across the range of test conditions. METHODS Description of Hood and Laboratory Space The nano fume hood evaluated has interior dimensions of 20.3 inches (51.6 cm) (height) × 32 in (81.2 cm) (width) with an internal working depth of 30 in (76.3 cm) and a face opening of 9.5 in (24.1 cm) (height) × 32 in (81.2 cm) (width). The hood is constructed out of cast acrylic with a phenolic resin base. The enclosure includes a variety of features to reduce turbulence and improve containment performance. Molded airfoils are included at both sideposts, at the base of the hood inlet, and along the bottom of the hood sash. This enclosure was based on a pharmaceutical balance enclosure designed to protect workers during the handling of active pharmaceutical ingredients and to provide a low turbulence environment for weighing of materials on microbalances. This hood was located in a laboratory which was 10.5 feet (3.2 m) wide by 21 ft (6.7 m) deep with a ceiling height of 9.4 ft (2.9 m). A 2 ft (61 cm) × 2 ft (61 cm) ceiling-mounted supply air diffuser was located at the center of the room and slightly to the left of the hood face (Figures 1a and b). Ventilation measurements Airflow measurements were taken to characterize the inlet air flow profile at the face of the nano fume hood. A traverse of the hood face with a hot wire anemometer was conducted to evaluate the spatial and temporal variation in air velocities entering the hood. The air J Occup Environ Hyg.