TY - JOUR
AU - Urban, Jeffrey J
AB - Abstract A fume hood is the most central piece of safety equipment available to researchers in a laboratory environment. While it is understood that the face velocity and sash height can drastically influence airflow patterns, few specific recommendations can be given to the researcher to guide them to maximize the safety of their particular hood. This stems from the issue that fundamentally little is known regarding how obstructions within the hood can push potentially harmful particles or chemicals out of the fume hood and into the breathing zone. In this work, we demonstrate how the position of a typical nanoparticle synthesis setup, including a Schlenk line and stir plate on an adjustable stand, influences airflow in a constant velocity fume hood. Using a combination of smoke evolution experiments and the aid of computational fluid dynamics simulations, we show how the location and height of the reaction components impact airflow. This work offers a highly visual display intended especially for new or inexperienced fume hood users. Based upon our studies and simulations, we provide detailed guidance to researchers and lab technicians on how to optimally modify reaction placement in order to protect the breathing zone while working. breathing zone, CFD, fume hood, Schlenk, synthesis Introduction Nanoparticles are becoming increasingly common commercially (Kwon and Kim, 2006; Pardeike et al., 2009; Zamkov, 2017). Unfortunately, many of these materials are known to cause a wide variety of health problems (Dieter et al., 1993; Buzea et al., 2007; Kim et al., 2007; Mühlfeld et al., 2007; Poland et al., 2008; Bilberg et al., 2010; Fröhlich, 2012; Khatri et al., 2013). This is especially alarming for researchers developing nanoparticles (Schulte and Salamanca-Buentello, 2007; Schulte et al., 2009; Kumar et al., 2010; Kuhlbusch et al., 2011; Lee et al., 2011; Broekhuizen et al., 2012; Pietroiusti and Magrini, 2014; Wu et al., 2014) as the properties of inherently safe materials in bulk sizes may unexpectedly become hazardous on the nanoscale. As a result, it is crucial that laboratories safeguard the breathable air in a researcher’s work space and ensure that work areas are assessed and deemed safe. Beyond personal protective equipment, a fume hood is inarguably the most essential safety tool at a synthetic researcher’s disposal (Tsai et al., 2009; Mattox et al., 2017), so it is imperative that fume hoods used for chemical synthesis do not inadvertently leak nanoparticles and hazardous chemicals into the air (Ding et al., 2017). There are many styles and configurations of fume hoods, but there is no one-size-fits-all option for various fields of research (i.e. organic chemistry, biological research, inorganic chemistry, etc. all perform different operations). However, it is widely accepted that a fume hood face velocity of 80–120 ft/min is ideal for preventing nanoparticles in a hood from entering the breathing zone of a laboratory (Spinazzè et al., 2016). Unlike constant flow fume hoods, which have no features to control the face velocity when the sash is moved (Domat et al., 2017), constant velocity hoods maintain their velocity regardless of sash height (Vinches et al., 2017). The constant velocity feature is a marvelous achievement toward improving laboratory safety conditions, but their extreme ease of use may lead researchers to become complacent with regard to safety. It is well known that a constant velocity fume hood can easily keep nanoparticles out of the lab air, and several groups have modeled how external obstructions (Hu et al., 1996; Lan and Viswanathan, 2001) and workers moving their arms across the fume hood threshold impact airflow patterns (Karaismail and Celik, 2010). Unfortunately, the most pragmatic case remains unexamined—that is, the influence of a typical synthetic reaction setup on airflow remarkably has yet to be explored. The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. 110–2016 (ASHRAE) method of testing fume hood airflow is the industry standard in the USA (American Society of Heating, 2016). In this method, a mannequin with particle detectors is placed in front of a fume hood and a sulfur hexafluoride tracer gas is released through a gas ejector placed 6” from the hood face. According to ASHRAE, the breathing zone test height must be 22” (the average height of fume hood operators in the USA) from the work surface and particle concentrations measured digitally by the mannequin. This standard outlines steps to take in order to ensure that an empty fume hood is operating properly and not forcing air back into the breathing zone. The ASHRAE standard focuses on testing hood performance in an empty fume hood and does not take into account airflow obstructions resulting from a chemical reaction setup located within the hood space. When an object is placed in the fume hood, such as a Schlenk line or stir plate used for synthesis, the airflow pattern changes. In some cases, these obstructions can force hazardous chemicals back into the breathing zone, creating a potentially unsafe condition for the researcher. In this manuscript, we explore how typical synthesis obstructions in a constant velocity fume hood may influence airflow and, consequently, movement of nanoparticles and hazardous chemicals throughout a hood. We released colored smoke from various positions in a hood containing standard reaction components (Schlenk line, stir plate, and sample box) to give a visual of how the airflow looks when a chemical release would be expected during a reaction. This work is intended to compliment the guidance provided by the ASHRAE standard by giving researchers, especially those new to fume hood use and unfamiliar with testing protocols, a clear visual of what happens within the hood when a chemical reaction inadvertently releases particles. Researchers in many locations operate under space-confined conditions or share fume hoods and, therefore, do not always fit the typical model of the US average of a 22” breathing zone to work space distance established by ASHRAE. In removing the mannequin and treating our experiments as though the smoke released is from an unattended reaction, we are able to focus solely on the influence of obstructions on airflow. We hypothesize that the synthetic reaction components influence the airflow within the hood and that the insights gained from this work will help researchers improve their laboratory air quality simply by controlling the reaction placement within the volume of a fume hood. We report that a Schlenk line, stir plate, and sample box change airflow patterns, as observed in computational fluid dynamics (CFD) simulations, and show using colored smoke that the airflow is significantly impacted not only by the sash position but also by the height of the reaction. Materials and methods The fume hood smoke plume experiments were designed to provide readily discernable, informationally dense data (i.e. mesh sizes in CFD simulations are larger than fine-grained changes in experimental smoke plume evolution) on fume evolution in realistic lab environments. Colored smoke provides immediate visual feedback on the spatial and temporal evolution of effluent plumes and can be used to test the validity of the CFD simulations. Our smoke plume experiments involved 6” red and blue smoke sticks (Ox Fireworks) and 1” smoke balls or smoke “candles” of various colors (Joker). It is important to note that changing the color of the smoke did not change the physiochemical properties. Preliminary tests showed that the color did not change our observations of smoke movement through the fume hood regardless of sash height or smoke color. All of the experiments in this work were carried out at the Molecular Foundry of Lawrence Berkeley National Laboratory in the same constant velocity fume hood with internal floor dimensions of 63” wide × 34” deep and two 10” wide sliding vertical sashes (Fig. 1). The fume hood contained three fixed baffles in the rear, a 12” sample box and Kimwipe box mounted on the left wall, and was equipped with a metal support lattice made of 1/2” steel bars (VWR) installed 10” from the rear of the hood. The room temperature was 22°C and face velocity through the fume hood was maintained at 105 ft/min. All photographs were taken using a Pentax K-70 DSLR. Figure 1. Open in new tabDownload slide Illustration displaying various parts of a traditional constant velocity fume hood and the breathing zone of a researcher. Image includes the fume hood with airfoil, baffles, and sashes, as well as a typical reaction setup, including a stir plate and Schlenk line on a traditional support lattice. Figure 1. Open in new tabDownload slide Illustration displaying various parts of a traditional constant velocity fume hood and the breathing zone of a researcher. Image includes the fume hood with airfoil, baffles, and sashes, as well as a typical reaction setup, including a stir plate and Schlenk line on a traditional support lattice. Models of the fume hood, stir plate (represented by an 8” cube), Schlenk line, and support lattice were drawn to scale using Sketchup. Fig. 1 shows a typical fume hood setup used for chemical synthesis, which includes a Schlenk line supported by a lattice framework and a stir plate slightly raised on a jack (represented by the white cube). Though a mannequin was not used in this study, a stick figure is shown in the figure to show what is typically considered the breathing zone height in the USA. Fig. 2 shows the general movement of air through the fume hood (excluding air currents in the top of the hood for the sake of simplicity). Looking at this side view (Fig. 2A), (i) air enters from the right, (ii) moves around the Schlenk setup and between the baffles (which reduce turbulence (Hu et al., 1998)), (iii) moves up along the rear of the hood, then (iv) exits through the top. Air enters the fume hood only via two routes (Fig. 2B): (i) through an opening created by raising the hood sash and (ii) constantly under the airfoil, (Tsai et al., 2010) (Tseng et al., 2006), while the only exit is through a rectangular opening at the top rear of the hood (Fig. 2C). Figure 2. Open in new tabDownload slide (A) Side-view illustration of fume hood with arrows showing general path of airflow (i) entering the fume hood, (ii) moving around the reaction setup and through between the baffles, (iii) moving up through the back of the hood, and (iv) exiting into the building’s exhaust system; (B) illustration of air entering under the airfoil and under the open sash above the airfoil; and (C) illustration showing only air exit point of fume hood. Illustrations are all drawn to scale. Figure 2. Open in new tabDownload slide (A) Side-view illustration of fume hood with arrows showing general path of airflow (i) entering the fume hood, (ii) moving around the reaction setup and through between the baffles, (iii) moving up through the back of the hood, and (iv) exiting into the building’s exhaust system; (B) illustration of air entering under the airfoil and under the open sash above the airfoil; and (C) illustration showing only air exit point of fume hood. Illustrations are all drawn to scale. The CFD simulations were designed to replicate the conditions in the experimental study and to help develop a reliable simulation framework for optimizing conditions within the hood. The realizable k-ε turbulence model, which simulates flow conditions involving turbulent kinetic energy (k) and the rate of kinetic dissipation (ε), combined with enhanced wall treatment to predict the airflow field. The double-precision solver of a commercially available code, ANSYS Fluent 18.0, was employed to iteratively solve the governing equations. The incoming air was introduced to the domain from a volume-flow inlet boundary and exited via a pressure based outlet. No-slip boundary conditions were used for the solid fume hood walls. The QUICK scheme (Leonard and Mokhtari 1990) was adopted for the discretization of the equations and the SIMPLE algorithm was used to couple pressure and velocity. This algorithm obtains the pressure field by enforcing mass conservation based on a relationship between velocity and pressure corrections. The computational domain was divided into about 6 million grids using ICEM CFD software. A sensitivity analysis was performed making sure that the grid was sufficiently fine and the results were independent of its size. The CFD results were regarded as converged and the iterations were terminated when the residual flattened out with no further reduction. In this stage, root-mean-square (RMS) residuals of all equations fall below 10–5, except the continuity equation which was below 10–3. At the same time, pressure and velocity magnitude were monitored at three points close to the air inlet, outlet, and fin walls to monitor the convergence of the solution. In order to improve upon our understanding of how a standard synthesis setup impacts a researcher’s breathing zone, it was important to determine how traditional Schlenk reaction components impact airflow patterns. Using colored smoke candles and smoke sticks to make visualization possible, the airflow was observed and photographed for the following fume hood conditions: (1) Empty: completely unobstructed; (2) Wall obstruction: standard sample box installed on hood wall; (3) Stir plate obstruction: stir plate on support jack, using raised and lowered positions to mimic synthetic operations; (4) Schlenk line obstruction: all major components of a standard synthetic setup. For all fume hood conditions, smoke was released within the hood and observed for four varying hood sash heights (Fig. 3A), which mimic the sash positions routinely used by researchers performing synthetic experiments. The sash heights (distance from the hood floor to sash bottom) are labeled S-1 through S-4 and range from 28” (S-1) to 0” (S-4; closed). Initial tests showed no change in smoke observations when using a single smoke stick for multiple sash positions versus allowing to burn and extinguish completely before testing the next sash height. For consistency, a single smoke stick was used for multiple sash heights. Smoke was released in each of nine positions from a single smoke stick as designated by the stars in Fig. 3B, starting with the hood fully open and waiting 5 s to ensure arm movement from adjusting the sash was not a factor before moving the sash to the next lowest position until the experiment was completed. Sash remained lowered for approximately 5 min after smoke stick was extinguished. Three positions were selected in the center of the hood (31.5” from the hood wall) to mimic where single reactions are typically performed. We also observed smoke release from three positions on each side of the fume hood (10” from the hood wall), where additional apparatuses may be placed in a busy hood, maximizing the available space. The side positions selected were as close to the hood wall as feasible because of the size of the stir plate and the location of the vacuum tubing port in the back right of the hood. Figure 3. Open in new tabDownload slide (A) Side view of fume hood sash heights used for experiments and (B) top-down view of the fume hood floor showing positions where smoke was released (stars) and the corresponding distances (dashed lines) from the very back of the fume hood. Figure 3. Open in new tabDownload slide (A) Side view of fume hood sash heights used for experiments and (B) top-down view of the fume hood floor showing positions where smoke was released (stars) and the corresponding distances (dashed lines) from the very back of the fume hood. Results and discussion Smoke experiments were first observed in an empty fume hood to establish a baseline for unobstructed airflow circulating through the hood. Fig. 4 shows smoke released in the front right of the fume hood. At sash heights S-1 and S-2, the smoke moved toward the back right corner of the fume hood and exited under and around the top two baffles. At lower sash positions, the smoke dispersed throughout the hood rather than immediately exiting through the baffles, which is most noticeable at heights S-3 and S-4. It is clear that the operating sash height (S-1) is best at removing smoke without much dispersal throughout the hood. Figure 4. Open in new tabDownload slide Smoke flow resulting from varying sash heights with lit smoke stick in front right of fume hood. Sash heights are 28” (S-1), 18” (S-2), 9” (S-3), and closed (S-4). Figure 4. Open in new tabDownload slide Smoke flow resulting from varying sash heights with lit smoke stick in front right of fume hood. Sash heights are 28” (S-1), 18” (S-2), 9” (S-3), and closed (S-4). Fig. 5 shows smoke release from the very center of the empty fume hood floor, the preferred location for researchers where most reactions take place. The results were the same as those reported for smoke released at the front right, only the smoke was removed more quickly and did not concentrate as much throughout the hood. In this case, completely exhausting the smoke with a closed sash took only about 30 s once the smoke stick had burned out compared to <5 min when the smoke stick was positioned in the front right. It is clear that the removal of smoke emitted from the center of the hood was much more efficient in this position, which is ideal since most synthetic processes are performed in this work space. Similar observations were made for all smoke stick positions in the far back as well as across the center (see Supplementary Information), and the back most positions allowed very little dispersion even with a closed sash (S-4). Figure 5. Open in new tabDownload slide Smoke flow resulting from varying sash heights with smoke stick in very center of fume hood. Sash heights are 28” (S-1), 18” (S-2), 9” (S-3), and closed (S-4). Figure 5. Open in new tabDownload slide Smoke flow resulting from varying sash heights with smoke stick in very center of fume hood. Sash heights are 28” (S-1), 18” (S-2), 9” (S-3), and closed (S-4). In order to see how a single obstruction installed in an otherwise empty fume hood might impact the airflow, smoke was released directly under a sample box installed on the left wall of the hood (Fig. 6). The smoke was observed crossing the sash threshold and entered into the breathing zone with a completely raised sash (S-1), and the smoke smell was very noticeable in the laboratory air. This was not observed when the smoke stick was positioned at the same location in an empty hood. These results suggest airflow is indeed disrupted by such an obstruction and imply that it is best not to perform chemistry directly under installed equipment. Fortunately, at all lower sash heights (S-2–S-4), the smoke particles were completely contained. Thus, if a reaction must be located below a sample box on the hood wall, it appears that lowering the hood sash may protect the researcher. It is clear from these experiments that sash height S-2 is the most efficient for removal of smoke particles, while S-4 is most efficient at dispersing the particles throughout the hood. Though the following experiments were performed for all sash heights (see Supplementary Information), the remaining discussion will focus solely on smoke release from positions where chemistry typically occurs (in the front center of the hood). Figure 6. Open in new tabDownload slide Placement of smoke stick in front left under sample box with fume hood sash at positions S-1 and S-2. Sash heights are 28” (S-1) and 18” (S-2). Figure 6. Open in new tabDownload slide Placement of smoke stick in front left under sample box with fume hood sash at positions S-1 and S-2. Sash heights are 28” (S-1) and 18” (S-2). To further our understanding of how a typical synthetic setup might impact the breathing zone, we next looked at how airflow was impacted by introducing a stir plate. A support was used so the top of the plate was 8” from the hood floor, which mimics the actual position of a cooling reaction in a typical synthetic setup. Smoke was released on the stir plate in the center front of the fume hood, the nearest location to the breathing zone where a researcher might perform their synthesis, with a closed sash (S-4) to most easily observe smoke dispersion. As seen in Fig. 7, the smoke continually moved upward and dispersed across the middle of the hood space, exiting through all three baffles in the same manner as previously described for the smoke sticks. No smoke was seen to exit under the air foil but a slight smoke smell was detected, so it was not immediately clear if the obstruction of the plate in front of the hood caused smoke particles to enter the breathing zone. By contrast, repeating the experiment at a 14” raised sash height had a similar result, but the smoke moved upward more quickly and no smell was detected. Furthermore, repeating the experiment at both heights in the very center of the hood caused the smoke to immediately move up and toward the back of the hood. As a result, only the 8” height obstruction in the center front was suspected with regard to airflow being pushed into the breathing zone. Figure 7. Open in new tabDownload slide Progression of smoke flow with smoke released from top of raised stir plate (8” tall) in front center of fume hood sash completely closed (S-4). Figure 7. Open in new tabDownload slide Progression of smoke flow with smoke released from top of raised stir plate (8” tall) in front center of fume hood sash completely closed (S-4). In order clarify whether or not the stir plate obstruction impacted the breathing zone, we ran CFD simulations of the fume hood including an 8” cube (stir plate) obstruction in the center front of the hood with the sash both closed (S-4) and at the vendor suggested standard operating height (S-2). Fig. 8 shows the simulated velocity on a plane at the hood center. As seen in the velocity contour plot with a closed sash (S-4; Fig. 8A), air enters under the airfoil and immediately hits the stir plate, increasing the velocity of the air moving upward along the sash toward the hood ceiling while reducing the velocity along the hood floor. A similar result was seen with an open sash (S-2; Fig. 8B). However, the additional input of air reduces the velocity along the sash as the airflow moves upward, which in turn changes the airflow pattern at the top of the hood. Interestingly, the vector model of a stir plate-obstructed hood with a closed sash (S-4) shows that some of the air entering from under the air foil is forced back out of the hood and into the breathing zone (Fig. 8C). Though we could not see colored smoke exiting in this hood configuration, this model explains why the smoke could be smelled within the lab and supports the suspicion that smoke particles entered the breathing zone. Furthermore, a raised sash (S-4) allowed enough air to enter into the hood that the stir plate did not force air back under the air foil (Fig. 8D). These results suggest that even with an obstruction blocking a portion of the center front of the fume hood, raising the sash may prevent the release of chemicals involved in a synthesis from entering the breathing zone. Figure 8. Open in new tabDownload slide CFD simulations of airflow patterns for middle segment of a constant velocity fume hood containing only an 8” stir plate obstruction (black cube) showing velocity models with the hood sash in the (A) closed and (B) 18” open position. Vector models with the hood sash in the (C) closed, and (D) open position. Figure 8. Open in new tabDownload slide CFD simulations of airflow patterns for middle segment of a constant velocity fume hood containing only an 8” stir plate obstruction (black cube) showing velocity models with the hood sash in the (A) closed and (B) 18” open position. Vector models with the hood sash in the (C) closed, and (D) open position. Many reactions rely on the use of a Schlenk line in addition to a stir plate, which adds more complexity to the obstructions in a fume hood. To better represent an actual synthetic setup, we installed a Schlenk line on the hood’s support lattice in our standard operating position. In a typical synthesis, reaction flasks are clamped to a support lattice and the stir plate is raised so that, upon completion of a heating reaction (e.g. using a removable heating mantle), the stir plate can be quickly lowered to accommodate a water bath to facilitate cooling (Mattox et al., 2014) (Urban et al., 2007). To mimic this height, the smoke candle experiments were repeated with the stir plate in the center of the fume hood raised such that the smoke was released from a stir plate 14” above the fume hood floor, which is typical for many synthetic protocols. Fig. 9A shows an example of a raised smoke experiment with a Schlenk line installed in the hood. With a closed sash (S-4), the smoke dispersed mostly throughout the upper portion of the hood before exiting through the baffles. The result suggests that a higher sample height allows efficient removal of particles by the fume hood regardless of the Schlenk line obstruction (see Supplementary Information for additional images). It’s likely that the simple act of raising a reaction could improve safety by protecting the breathing zone with more efficient removal of chemicals from the hood, regardless of the sash height. Figure 9. Open in new tabDownload slide Smoke released with closed sash from the following: (A) 14” raised stir plate, (B) a lowered stir plate with Schlenk line installed, and (C) from a lowered stir plate in an empty fume hood. Figure 9. Open in new tabDownload slide Smoke released with closed sash from the following: (A) 14” raised stir plate, (B) a lowered stir plate with Schlenk line installed, and (C) from a lowered stir plate in an empty fume hood. Smoke experiments were repeated with the Schlenk line and stir plate obstruction with a lowered stir plate, 8” from the fume hood floor, which is the typical cooling position for many reactions. Smoke was released once more in the center front of the hood. Interestingly, the Schlenk line caused a very obvious change to the airflow when smoke was released at this lowered position. With a closed sash, the Schlenk line appeared to remove the particles through the back of the hood before they could widely disperse (Fig. 9B). Furthermore, no smoke smell was detectable in the breathing zone of the lab, which was not the case with only a stir plate obstruction present in an empty hood (Fig. 9C). Repeating the experiment with a raised sash had a similar result, with the smoke being directed more downward with the Schlenk line than without it and again no notable smoke or smell entered the breathing zone (see Supplementary Information). This supports the hypothesis that the synthetic reaction components influence the airflow within the hood. Comparing the CFD model of a fume hood with only a stir plate obstruction (Fig. 10A) to a model with a Schlenk line added (Fig. 10B) makes the differences in airflow very clear. Note that Fig. 10 displays models with sash height S-2, as this is the most common position used during synthesis (see additional models in the Supplementary Information). As seen in the velocity and vector images in Fig. 10B, air patterns change to circulate not only around the outer edges of the fume hood but also around the support lattice and Schlenk line (additional images in the Supplementary Information). The Schlenk line also causes the air to move toward the front of the hood and down more quickly than in an empty hood, which is in agreement with our observation of the smoke appearing to be forced more in a downward direction when released from an 8” stir plate. Figure 10. Open in new tabDownload slide Velocity vector and velocity CFD models of a constant velocity fume hood with an open sash (A) with only a stir plate and (B) with a stir place and Schlenk line on a support lattice (black cube in model represents stir plate on lowered jack). (C) Left segment of velocity CFD models of a constant velocity fume hood with an open sash (S-2) (left) with only an 8” raised stir plate as the only obstruction and (right) with and Schlenk line installed (black cube in model represents stir plate on lowered jack). Figure 10. Open in new tabDownload slide Velocity vector and velocity CFD models of a constant velocity fume hood with an open sash (A) with only a stir plate and (B) with a stir place and Schlenk line on a support lattice (black cube in model represents stir plate on lowered jack). (C) Left segment of velocity CFD models of a constant velocity fume hood with an open sash (S-2) (left) with only an 8” raised stir plate as the only obstruction and (right) with and Schlenk line installed (black cube in model represents stir plate on lowered jack). The influence of the full synthesis setup is also obvious in the side segments of the CFD models as observed in Fig. 10C for the left segment of the fume hood. When the Schlenk line is included in the simulations, the velocity is reduced around the support lattice and the slower airflow extends more toward the center of the hood. This explains why the smoke lingered at the bottom of the hood before exiting through the lower baffles. With particle movement being so influenced by obstructions caused by typical reaction setups, it is especially important for researchers to be mindful of what they introduce into the hood space when there is a potential for release of chemicals while they work. Though the addition of a Schlenk line does not necessarily push air into the breathing zone, it does change the airflow surrounding the reaction setup and also influences the rate at which air moves away from the front of the hood. This means that if more particles and chemicals are released from a reaction into the air, they have more chances to mix together before exiting, which may cause problems depending on the hazards of the chemistry involved. Conclusions This illustrative work should be especially useful to researchers new to fume hood use and provides insight into how the locations of typical Schlenk reaction components influence fume hood airflow using colorful smoke as a visual aid. The results are intended to compliment the ASHRAE method, which is widely accepted as the US method for hood performance testing; in this case, we are focusing solely on the visual aspect of airflow changes by releasing smoke only from positions where chemistry occurs. By coupling the visual observations of smoke experiments with CFD simulations, we determined that common reaction components (a stir plate, sample box, and Schlenk line) can be positioned in such a way as to force air beyond the hood sash and into the breathing zone of the researcher, causing a potentially dangerous situation. Furthermore, we found that a Schlenk line may also bring about potential unsafe conditions by drastically changing the airflow patterns around the tubing and glassware, allowing any released chemicals additional time to mix before removal compared to an empty fume hood. In order to protect the breathing zone of the researcher, it is important to minimize the obstructions in a hood, taking into account the impact of stir plates and Schlenk lines and keeping the airfoil and sash openings unobstructed. We offer the following recommendations to researchers in order to help protect their breathing zone when working with chemicals in a constant velocity fume hood: (1) Keep the sash height slightly lowered (S-2; 18”) to efficiently remove any released particles. (2) Move reactions out from under sample boxes and other equipment installed on hood walls. (3) Keep reactions as far back in the hood as feasible. (4) Raise reactions slightly (above 8”) whenever possible. (5) Be mindful that Schlenk lines keep airflow more concentrated around the reaction setup, so more mixing of chemicals is likely than in an obstruction-free hood. When researchers practice integrated safety management while planning their chemical reactions, they should take into account how their reaction setup may have a negative impact within the hood and the breathing zone. Many researchers become complacent about safety when it comes to fume hood use, and it is our hope that this work will help raise awareness. Acknowledgements This work was completed at the Molecular Foundry, Lawrence Berkeley National Laboratory, a user facility supported by the Office of Science, Office of Basic Energy Sciences of the US Department of Energy under contract no. DE-AC02-05CH11231. Conflict of interest: The authors declare there is no competing conflict of interest involved with this work. References American Society of Heating RaA-CE, Inc . ( 2016 ) ASHRAE standard, an American National Standard. Method of testing performance of laboratory fume hoods . Atlanta, GA . 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TI - Impact of Source Position and Obstructions on Fume Hood Releases
JF - Annals of Work Exposures and Health (formerly Annals Of Occupational Hygiene)
DO - 10.1093/annweh/wxz062
DA - 2019-10-11
UR - https://www.deepdyve.com/lp/oxford-university-press/impact-of-source-position-and-obstructions-on-fume-hood-releases-6vkLEJwLAx
SP - 937
EP - 949
VL - 63
IS - 8
DP - DeepDyve
ER -