INCREASING FUME HOOD SAFETY BY ELIMINATING ALL BENCH-LEVEL OBSTRUCTIONS Synthcon, LLC | 770 Wooten Rd., Unit 101, CO Springs, CO 80915 | 719.429.5376 Copyrighted Material © 2021 The Problem is Fume Exhaust Abstract This document will discuss the Pathway Obstruction importance of understanding Fume hoods are, first and foremost, safety devices. Their use should what affects efficient fume be carefully thought out to fit the user's specific needs. An amazing exhaustion from a chemical fume variety and quantity of equipment is often seen being used inside a hood and how to maximize the fume hood. Surprisingly, most volatile chemicals used inside a fume effectiveness of any existing fume hood produce vapors more dense than air; dense vapors will tend to hood by integrating a simple, sink while exiting the fume hood. Unfortunately, many bench single engineering control safety surfaces contain equipment that severely impedes direct, efficient measure to assure maximum fume exhaustion (airflow). This practice is so wide spread that it has exhaustion in any fume hood use become second nature to scientists who use fume hoods. The photograph above shows what a bench surface should and can look scenario. This new category of like with the same equipment still being used inside the hood, but safety devices is leading the way with the hood's lab bench surface free of equipment and chemical toward safer fume hood use for obstructions. More on this patent-pending, new category of safety all users. devices later in the paper. Let's take a closer look at the problem and then the solution. 2 Synthcon, LLC | 770 Wooten Rd., Unit 101, CO Springs, CO 80915 | 719.429.5376 Copyrighted Material © 2021 Some fume hoods have multiple baffles (e.g., entry points into the exhaust system) arranged at different heights in the rear of the hood. Preventing dense fumes from sinking to the lowest point to exit requires the internal airflow pattern to be fast enough to force denser-than-air fumes to rise or maintain a level path in order to exit the hood through an opening that is NOT the bottom baffle. This is often attempted by placing the fume- generating equipment or chemicals close to the rear part of the hood. If equipment or chemicals rest directly or indirectly on the lab bench, the primary exit pathway will be obstructed, impeding fume exhaustion. Much of the equipment used in a fume hood rests on the bench surface, even those items elevated using lab jacks, ring stands or clamps. Lab jacks and ring stands take advantage of the vertical space, but have a large footprint on the bench. Lattice materials usually represent only small obstructions, unless they are anchored to the bench surface using a larger brace or bracket. 3 Synthcon, LLC | 770 Wooten Rd., Unit 101, CO Springs, CO 80915 | 719.429.5376 Copyrighted Material © 2021 Unfortunately, Obstructions are the Norm, not the Exception. When fume hazards are invisible and accidents happen in someone else's lab, there is a tendency for complacency to set in. It can be difficult to fix what is not perceived as broken. Proof that problems exists: In 2018, the Chemical Safety and Hazard Board (CSB) published a list of 260 laboratory accidents from January 2001 - July 2018, resulting in 10 deaths and 507 injuries. The board also produced a video entitled: "Experimenting with Danger," which focuses on three university laboratory accidents. Ref. 1 | csb.gov/assets/1/6/csb_laboratory_incident_data.pdf Ref. 2 | csb.gov/csb-releases-new-video-on-laboratory-safety-at-academic- institutions 4 Synthcon, LLC | 770 Wooten Rd., Unit 101, CO Springs, CO 80915 | 719.429.5376 Copyrighted Material © 2021 Know Your Equipment and How it Works Awareness Training It is up to the hood There is no excuse for not user to know how knowing how to use the to use their equipment or how it works. equipment and This is the employer or how their educational institution's equipment works. responsibility to determine a worker's knowledge level and to teach them if necessary. Fume hoods are non-airtight safety devices that contain and then exhaust all generated fumes away from the lab space and workers inside the building. A hood user's actions can greatly impact the efficiency and effectiveness of any fume hood. By knowing how a fume hood works and knowing how the user's actions affect the hood's performance, a fume hood user can work safely without endangering themselves or others. Ironically, very few examples of thorough fume hood training exists at the university level. 5 Synthcon, LLC | 770 Wooten Rd., Unit 101, CO Springs, CO 80915 | 719.429.5376 Copyrighted Material © 2021 Side View of Fume Hood Airflow Patterns Under Different Fume Hood Use Scenarios (A) Sash closed, no equipment, a completely empty hood (B) Sash open to its working height, no equipment (C) Sash open, typical equipment placement (resting on bench surface). Obstruction item doesn't allow flow underneath to exit; requires rerouting of fumes and some fumes bounce back toward open sash and user. A-C: Effects are magnified with increasing number of items and/or increasing size of items on the bench (common and traditional use of a fume hood). D & E: MAC Hood Support Installed (D) Equipment elevated using a MAC hood support (simultaneous elevator safety device), sash closed (E) Equipment elevated using a MAC hood support (simultaneous elevator device), sash open D & E: Fumes can flow underneath all equipment exhausting quicker than without the device installed. A-C: Fume Hood Airflow in Typical Use Scenarios (A) Strong airflow pattern travels downward along interior sash window then merges with horizontal flow entering from the airfoil and travels along the lab bench surface to exit through the bottom baffle opening; fume direction reversal observed due to pattern change. (B) Fumes entering through sash opening split into a "<" pattern, with less dense fumes exhausting through the middle or upper baffle openings and dense fumes sinking and exiting through the bottom baffle opening. (C) Each individual object resting on the hood's bench surface causes an obstruction to direct fume exhaustion. Dense fumes are forced to go around, over the top, or deflect backward. D & E: Airflow With a MAC Hood Support Installed (D) All equipment is simultaneously elevated off the bench surface and rests above the dedicated air space created by the device. Unobstructed (unimpeded) air continuously flows along the bench surface, underneath ALL EQUIPMENT toward the bottom baffle exit. Individual upward, downward, and horizontal airflows are possible underneath all equipment, irrespective of the amount of equipment elevated. (E) Air continues to flow underneath all equipment and exit along the bottom baffle, while additional exhaustion of lighter vapors may occur at the middle and upper baffle exits. 6 Enhanced fume exhaustion ability is only available from Synthcon LLC. Synthcon, LLC | 770 Wooten Rd., Unit 101, CO Springs, CO 80915 | 719.429.5376 Copyrighted Material © 2021 Since many fumes are not visible, they can easily go undetected and back out of the hood due to any combination of poor equipment placement, fume quantity, fume generation location, and/or number and size of equipment pieces resting on the lab bench surface blocking the major exhaust pathway for dense fumes. 7 Synthcon, LLC | 770 Wooten Rd., Unit 101, CO Springs, CO 80915 | 719.429.5376 Copyrighted Material © 2021 (A) Dense fumes generated with equipment blocking the exit pathway - sash at working height and fumes wandering around objects to find an exit point. (B) Equilibrated airflow pattern for dense fumes after sash is closed. (C) A transitory "wave-like" airflow pattern lasting several seconds the moment the sash is closed; internal airflow is now more concentrated along the bench surface as the upper air intake area (sash opening) is eliminated, resulting in internal airflow pattern changes. 8 Synthcon, LLC | 770 Wooten Rd., Unit 101, CO Springs, CO 80915 | 719.429.5376 7 Copyrighted Material © 2021 Flow Above Containers Flow at Bench Level Upper Photo: With the sash open to the working height dense fume rise and escape the container then sink as they flow along the bench surface and exit through the bottom baffle opening. Lower Photo: With the sash closed or closing, fumes generated in the front and middle regions of the hood actually reverse direction and are carried toward the interior surface of the sash where the rapid downflow pattern merges with the incoming airfoil air supply traveling backward toward the exit. This is best viewed by videotaping visible movement patterns during testing. 9 Synthcon, LLC | 770 Wooten Rd., Unit 101, CO Springs, CO 80915 | 719.429.5376 Copyrighted Material © 2021 Dense fumes easily sink through spaces in a Multiple Air Channel (MAC) Hood Support safety device and in between the interior sash surface and front edge of the device when the sash is closed. This rapid, downward airflow merges with the fast horizontal air entering the hood underneath the lip (through the airfoil). The merged flow travels underneath all equipment along the lab bench surface and out the bottom baffle opening (exit). The airflow underneath all of the equipment is continuous irrespective of any sash position. 10 Synthcon, LLC | 770 Wooten Rd., Unit 101, CO Springs, CO 80915 | 719.429.5376 Copyrighted Material © 2021 (A) Dense fumes escape traveling backward and sinking as they approach the rear of the hood. (B) When the sash is at a point lower than the level of fume generation, the changing hood's internal airflow pattern forces fumes forward and strongly downward toward the bench surface. (C) Dense fumes from a flask positioned close enough to the middle baffle; fumes simply travel laterally and exit the hood.