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. Author manuscript; available in PMC: 2022 Sep 1.
Published in final edited form as: Morphologie. 2020 Dec 2;105(350):237–246. doi: 10.1016/j.morpho.2020.11.002

Local exhaust ventilation systems for the gross anatomy laboratory

Systèmes de ventilation par aspiration locale pour un laboratoire d’anatomie générale

Matthew J Zdilla 1,2,3,*
PMCID: PMC8169711  NIHMSID: NIHMS1647246  PMID: 33279395

Summary:

The inability to exhaust airborne formaldehyde and other volatile organic compounds from a gross anatomy laboratory is an impediment to gross anatomical education. Despite the importance of removing harmful airborne chemicals, there is scant information regarding how to build effective local exhaust ventilation systems. In this study, various exhaust systems were built and assessed for exhaust flow, airborne formaldehyde removal, and noise production with the aim of identifying inexpensive and simple exhaust systems that can create a healthy and quiet exhaust flow from a downdraft dissection table. The results of the study include details regarding 11 local exhaust ventilation systems, including an exhaust system that produces an exhaust flow of 777cfm, allows no detectable airborne formaldehyde (0ppm) despite a 1000mL pool of formalin (composed of 37% formaldehyde) positioned directly beneath a formaldehyde-meter, and operates at a very low noise level (maximum of 69.2dBA with coexisting baseline room noise of 38.6dBA). Furthermore, the aforementioned local exhaust ventilation system costs less than $400 (USD) to build and can be assembled in a matter of minutes with minimal know-how. The local ventilation systems assessed in this study were capable of down-drafting air away from the breathing zone; therefore, the utilization of such local ventilation systems may have the additional benefit of decreasing the person-to-person transmission of aerosolized pathogens. This information marks an improvement in laboratory health and safety measures, facilitates the creation of gross anatomy laboratories, and improves access to gross anatomical education.

Keywords: anatomy, cadaver, formalin, formaldehyde, ventilation

Introduction:

Air quality is of the utmost importance in a gross anatomy laboratory. Cadaveric materials are typically fixed with embalming fluids that contain harmful volatile organic compounds (VOCs) such as formaldehyde― a chemical that has recently been classified as a carcinogen [1–4]. Indeed, myriad negative health effects can manifest among individuals exposed to volatile organic compounds in a gross anatomy laboratory, even with short-term exposure [5,6]. Therefore, the presence of volatile organic compounds in a gross anatomy laboratory may affect the capacity for optimal learning, teaching, and research activities among the students, staff, and faculty within the gross anatomy laboratory. Furthermore, because of the health risks associated with exposure to VOCs, the inability to exhaust airborne VOCs from a laboratory is an impediment to the creation of gross anatomy laboratories and gross anatomical education, in general [7,8].

Several organizations provide guidelines regarding airborne chemical exposure and its effects on human health. Such organizations include, but are not limited to, the American Conference of Governmental Industrial Hygienists (ACGIH), the Occupational Safety and Health Administration (OSHA), and the National Institute for Occupational Safety and Health (NIOSH). The unsafe levels of airborne chemical exposures identified by the ACGIH, OSHA, and NIOSH are typically listed in the Safety Data Sheet (SDS) which accompanies laboratory chemicals (i.e., embalming materials and re-wetting solutions).

The ACGIH defines so-called Threshold Limit Values (TLVs) in order to aid in air quality assessment. The TLVs include 1) a time-weighted average (TLV-TWA) which is defined as a “concentration for a conventional 8-hour workday and 40-hour workweek, to which it is believed that nearly all workers may be repeatedly exposed day after day, for a working lifetime without adverse effect”; 2) a short-term exposure limit (TLV-STEL) which is a 15-minute time-weighted average exposure that should not be exceeded at any time and; 3) a ceiling level (TLV-C) which is a maximum concentration that should not be exceeded during exposure (not an average) [9]. The OSHA defines Permissible Exposure Limits (PELs), which are values similar to the TLVs defined by the ACGIH. Some older OSHA PELs have been “vacated,” that is, retracted under court order and are accordingly referred to as Vacated Permissible Exposure Limits (VPELs). The NIOSH also defines thresholds similar to both ACGIH and OSHA, including the TWA and ceiling; however, the NIOSH also defines the level that is immediately dangerous to life or health (IDLH). The aforementioned values may differ between organizations. As an example, exposure guidelines for formaldehyde according to the ACGIH, OSHA, and NIOSH are summarized in Table 1 [9–11].

Table 1:

Formaldehyde exposure guidelines according to varied organizations.*

Organization IDLH (ppm) Ceiling (ppm) STEL (ppm) TWA (ppm)
ACGIH TLV - - 0.3 0.1
OSHA PEL - - 2 0.75
NIOSH 20 0.1 - 0.016
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*

Data acquired from the National Institute for Occupational Safety and Health (2014) and Occupational Safety and Health Administration (2019).

In addition to safety considerations regarding air quality, consideration must be given to ensure safe noise levels for the protection of hearing. Therefore, the noise generated by means of ventilation/exhaust must be taken into consideration in laboratory settings. For example, OSHA standards require that protection against noise be provided when sound levels exceed 90dBA TWA (8-hour), whereas NIOSH standards require protection when sound levels exceed 85dBA TWA [12].

Recently, the “Working Group for Reduction of Formaldehyde Exposure in Dissection Courses” of the Anatomische Gesellschaft reported guidelines regarding the reduction of formaldehyde in anatomy laboratories [13]. The group identified that the integration of exhaust of individual dissecting tables into the ventilation system of the anatomy building was “unavoidable” [13]. Certainly, effective, quiet, local exhaust of VOCs from cadaveric dissection tables is a valuable safety measure; however, there are scant reports providing specific details regarding how to build such local exhaust ventilation (LEV) systems. Therefore, this study assesses varied LEV systems with the aim of identifying simple and inexpensive exhaust systems that can create a healthy quiet exhaust flow.

Materials and Methods:

This study was conducted in the United States where it is customary for nomenclature regarding air handling materials such as fans and ducts to conform to United States customary units (e.g., inches, feet, cubic feet per minute), as opposed the International System of units employed in most scientific writing. This study, therefore, breaks with the conventional International System of units due to the nature of the materials used in building the exhaust systems utilized in the study. For the ease of reference, conversion factors are as follows: 1 inch (in) = 2.54cm; 12in = 1 foot (ft) = 0.3048m; 1cfm =1ft3/min = 1.699011m3/h.

Building the Exhaust Systems:

A total of nine exhaust configurations were built; the details regarding the schematics of each system may be found in Figure 1. Each system was able to be assembled and disassembled in a matter of minutes. In addition to duct tape, a screw driver, wire cutting pliers, and a tape measurer, the materials utilized to build the exhaust systems included two Hydroplanet™ 12-inch 1500cfm inline duct fans with built-in free variable speed controllers (American Seechance Inc., Ontario, CA); two VIVOSUN 6-inch 440cfm inline duct fans with variable speed controllers (VIVOSUN; Los Angeles, CA); two sheet metal duct reducers (12-inch to 6-inch) crimped on the small end (SHM Ducting, Part number: SHMSFT2812U); two packs of LOKMAN 12-inch stainless steel worm gear adjustable hose clamps (five clamps per pack); two 12.5-inch Hon & Guan stainless steel round bull nosed external extractor wall vent outlets (Shenzhen Hongguan Mechatronics Co., Ltd, Longhua District, Shenzhen); two Imperial 7.5-inch by 3.25-inch galvanized steel airtight adhesive duct take-offs (for 6-inch ducting) (Imperial Manufacturing Group, Richibucto, NB); one Hydro Crunch 12in by 25ft aluminum duct; one LamaFlex™ 6in by 25ft foil flexible duct (Lambro Industries, Inc., Amityville, NY); and one Ideal-Air™ 12-inch wye branch (Ideal Air, Vancouver, WA).

Figure. 1:

Figure. 1:

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Varied downdraft-table exhaust schemes. A: 5ft of 6in diameter duct > 6in inline duct fan > 2ft of 6in diameter duct > 6in diameter duct takeoff > external wall vent. B: 3ft of 6in diameter duct > 6in inline duct fan > 2ft of 6in diameter duct > 6in inline duct fan > 2ft of 6in diameter duct > 6in diameter duct takeoff > external wall vent. C: 5ft of 6in diameter duct > 12in to 6in duct reducer > 12in duct fan > 2ft of 12in diameter duct > external wall vent. D: 12in to 6in reducer > 5ft of 12in diameter duct > 12in duct fan > 2ft of 12in diameter duct > external wall vent. E: 3ft of 6in diameter duct > 12in to 6in reducer > 12in duct fan > 2ft of 12in diameter duct > 12in duct fan > 2ft of 12in diameter duct > external wall vent. F: 1ft of 6in diameter duct > 6in X 6in X 6in wye connector > two 5ft long 6in diameter ducts running in parallel > two 6-inch fans in parallel > two 2ft long 6in diameter ducts in parallel > two 6in diameter duct takeoffs in parallel > two external wall vents. G: 1ft of 6in diameter duct > 12in to 6in reducer > 1ft of 12in diameter duct > 12in X 12in X 12in wye connector > two 4ft long 12in diameter ducts running in parallel > two 12-inch fans in parallel > two 2ft long 12in diameter ducts in parallel > two external wall vents. H: 1ft of 6in diameter duct > 6in X 6in X 6in wye connector > two 5ft long 6in diameter ducts running in parallel > two 12in to 6in reducers in parallel > two 12-inch fans in parallel > two 2ft long 12in diameter ducts in parallel > two external wall vents. I: 3ft of 6in diameter duct > 6in X 6in X 6in wye connector > two 6-inch fans in parallel > two 2ft long 6in diameter ducts in parallel > two 12in to 6in reducers in parallel > two 12-inch fans in parallel > two 2ft long 12in diameter ducts in parallel > two external wall vents.

Testing the Air Flow from the Exhaust Systems:

A HoldPeak® 866B digital anemometer (Zhuhai JiDa Huapu instrument Co., Ltd.; Zhuhai, China; Resolution: 0.1m/s, 19ft/min; Accuracy: ±5%) was used to measure air velocity in each exhaust system with all fans on high speed as well as with all fans on low speed settings. Exhaust flow was then calculated as the product of the air velocity and area of the exhaust duct.

Testing the Exhaust Effectiveness by Measuring Airborne Formaldehyde Levels:

The “I” exhaust system, seen in Figure 1I, was affixed to a 6-inch flange on a downdraft dissection table (TBJ Model 32–86 DD-AT-M-AH; TBJ Inc., Chambersburg, PA).

An Extech FM200 formaldehyde meter (FLIR Commercial Systems Inc., Nashua, NH; Range: 0.00 to 5.00ppm; Resolution: 0.01ppm; Accuracy: ±5%) was mounted to a tripod and positioned 22in above the center of the dissection table, in order to approximate the breathing zone during dissection. A dissection tray with a length of 25in (63.5cm), width of 9in (22.9cm), and depth of 1in (2.54cm), having a total area 225in2 (1451.61cm2) was filled with 1000mL of “Formaldehyde laboratory Grade” (Item #86–3463, Carolina Biological Supply Company, Burlington, NC), composed of 37% formaldehyde, 10–15% methanol, and 48–53% water. The tray was placed in the center of the dissection table, directly beneath the formaldehyde meter, either flat on the table or atop a bucket which stood at 8in (20.3cm) (Fig. 2). The heights of the dissection tray were intended to represent vapors emitted from embalming fluids pooled at the surface of a dissection table as well as vapors emitted from the surface of an embalmed cadaver.

Figure. 2:

Figure. 2:

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To test airborne formaldehyde levels, a 37% solution of formaldehyde was placed in a 25 × 9 × 1in (63.5 × 22.86 × 2.54cm) dissection tray. A formaldehyde meter was positioned above the pool of formalin and continually monitored airborne formaldehyde levels. The location of the formaldehyde meter is representative of the typical location of a dissector’s face and the origins of vapors emitted from embalming fluids pooled on the surface of a dissecting table as well as from the surface of a cadaver. A: Airborne vapors tested at 21in (53.3cm) above the surface of a pool of formalin located at the surface of the dissection table. B: Airborne vapors tested at approximately 13in (33.02cm) above the surface of a pool of formalin located atop a bucket with an 8in (20.32cm) height.

The exhaust flow of configuration “I” was adjusted from high exhaust flow (all fans set to high speed), to the lowest possible exhaust flow (one 6-inch fan set to low speed). Formaldehyde levels were tested every minute for 15 minutes at each tested exhaust rate and average (Mean±SD) airborne formaldehyde levels were calculated accordingly. Because of safety risks, control tests were adapted to take place for an abbreviated time span wherein formaldehyde levels were tested every 15 seconds until airborne formaldehyde levels exceeded the OSHA STEL of 2ppm.

Testing Noise:

Noise was assessed with an HHSL402SD sound level meter (Omega Engineering Inc., Norwalk, CT). A-weighting, which mimics the response of the human ear, was applied to sound levels to best assess environmental sound. Slow time weighting (500ms) was applied to best assess the average sound from the ongoing process of fan operation. Noise was assessed by using the “I” system with all four fans on high speed and all four fans on low speed. Sound readings were taken in two locations: 1) just above the cadaver in accordance with the height of formaldehyde levels to simulate ear position during dissection and 2) 5ft (1.524m) above the ground, alongside the table, in order to approximate an individual standing alongside the dissection table. Noise exposure calculations were based upon current OSHA, NIOSH, and ACGIH standards.

Results:

The exhaust flows from each of the nine exhaust systems can be found in Table 2. A summary of airborne formaldehyde levels as a function of exhaust flow generated from varied fan speed settings from the “I” exhaust configuration can be found in Figure 3.

Table 2:

Exhaust flow generated by varied exhaust systems.

Exhaust System Flow (cfm) at Low Fan Speed Flow (cfm) at High Fan Speed
Control* 0* 0*
A 255 332
B 286 334
C 285 417
D 301 429
E 359 495
F 437 545
G 479 653
H 498 672
I 529 761
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*:

Measurement taken with anemometer held to downdraft table flange without exhaust system attached. Fan speed is not applicable.

Figure. 3:

Figure. 3:

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Airborne formaldehyde levels, emitted from a 1000mL pool of formalin (37% formaldehyde) located in a dissection tray positioned at the surface (A and B) and 8in above the surface of the dissection table (C and D). Exhaust flow was measured from the “I” exhaust system seen in Figure 1I using varied fan speeds. A: Results of a control experiment with no exhaust (0cfm) and a pool of formalin located on the dissection table surface. Measurements were taken every 15 seconds until formaldehyde levels exceeded the OSHA STEL of 2.0ppm, which occurred in less than three minutes. B: Average formaldehyde levels (Mean ± SD) as a function of exhaust flow. Formaldehyde levels were recorded every minute for 15 minutes / fan setting. C: Results of a control experiment with no exhaust (0cfm) and a pool of formalin located 8in above the dissection table surface. Measurements were taken every 15 seconds until formaldehyde levels exceeded the OSHA STEL of 2.0ppm, which occurred in less than one minute. D: Average formaldehyde levels (Mean ± SD) as a function of exhaust flow. Formaldehyde levels were recorded every minute for 15 minutes / fan setting. (ALPHA represents the OSHA TWA of 0.75ppm; BETA represents the OSHA STEL of 2.0ppm; and DELTA represents the current NIOSH TWA of 0.016ppm.)

The maximum exhaust flow among the nine prototypes was 761cfm, produced by the “I” configuration. The “I” configuration was able to generate 0ppm airborne formaldehyde levels with the pool of formalin (37% formaldehyde) located both on the table and 8in above the table. The “I” configuration was the only configuration capable of maintaining an airborne formaldehyde exposure level below the NIOSH TWA of 0.016ppm, regardless of the location of the formalin.

In the control experiments (i.e., formaldehyde measurements in the absence of any exhaust flow), formaldehyde levels elevated rapidly. When the formalin pool was located directly on the dissecting table, formaldehyde levels exceeded the OSHA STEL of 2.0ppm in less than three minutes in the absence of exhaust (Fig. 2A). When the formalin pool was located eight inches above the dissecting table, formaldehyde levels exceeded the OSHA STEL in less than one minute in the absence of exhaust (Fig. 2B).

All fan settings of the “I” configuration were able to reduce exhaust vapors to 0ppm from the formalin pool located at the surface of the table except for the setting wherein one 6-inch duct fan was set to its lowest speed (producing 174cfm) (Fig. 3). On the other hand, the only “I” configuration setting able to reduce airborne fumes to 0ppm, or below the NIOSH TWA of 0.016ppm with the formalin pool located eight inches above the table was when all four fans were set to high speed (producing 761cfm) (Fig. 3). Yet, average (Mean) levels below the OSHA TWA of 0.75ppm were produced by the following settings: two 12-inch fans set to low speed (exhausting 394cfm); all fans set to low speed (exhausting 491cfm); and two 12-inch fans set to high speed (exhausting 556cfm) (Fig. 3).

The baseline noise in the room (without downdraft ventilation) with the sound meter held both above the dissection table and alongside the dissection table was 38.6dBA. When all four fans of the “I” exhaust system were set to high speed, the noise level was 69.6dBA directly above the table and 65.5dBA alongside the table. When fans were all set to low speed the noise level was 63.6dBA directly above the table and 59.5dBA alongside the table. Therefore, an individual exposed to eight-hours of the maximum noise level (69.6dBA) from the “I” exhaust system would receive an OSHA noise dose percentage of 5.9%. Occupational noise doses and TWAs from the “I” exhaust configuration with all fans set to high speed according to OSHA, NIOSH, and ACGIH are summarized in Table 3.

Table 3:

Noise doses and eight-hour time weighted averages from the “I” exhaust configuration with all fans set to high speed.

Exposure Time (hr) at 69.6 dBA* OSHA† NIOSH / ACGIH ‡
Dose (%) TWA (dBA) Dose (%) TWA (dBA)
1 0.7 54.6 0.4 60.6
2 1.5 59.6 0.7 63.6
3 2.2 62.5 1.1 65.4
4 3.0 64.6 1.4 66.6
5 3.7 66.2 1.8 67.6
6 4.4 67.5 2.1 68.4
7 5.2 68.6 2.5 69.0
8 5.9 69.6 2.8 69.6
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*:

Sound level is that of the “I” configuration with all fans on high speed

†:

Criterion time = 8 hr; Criterion level = 90 dB; Exchange rate = 5 dB

‡:

Criterion time = 8 hr; Criterion level = 85 dB; Exchange rate = 3 dB

Discussion:

Historically, adequate laboratory ventilation has been one of the principal gross anatomy laboratory design concerns [7,8]. This report details the design and functional capacity of several LEV systems that are capable of eliminating harmful airborne volatile organic compounds. The systems are versatile and can be utilized in conjunction with downdraft tables or “snorkel” exhaust systems. They may also be used as a source of general exhaust from laboratories. This study is unique in its detailed description of simple, effective, and relatively inexpensive LEV systems. The LEV systems can make the creation of gross anatomy laboratories a possibility for institutions that would, otherwise, be hindered by financial obstacles or nonconductive infrastructure. Furthermore, the utilization of the LEV systems will improve safety in gross anatomy laboratories.

A wide variety of chemicals with varied levels of toxicity and health-related effects on humans are used in modern embalming [2,14,15]. Brenner [14] details myriad chemicals used in embalming including preservatives and fixatives such as aldehydes (e.g., formaldehyde, glutaraldehyde, glyoxal / oxaldehyde), tetrakis(hydroxymethyl)phosphonium chloride, 1-methyl-3-octyloxymethylimidazolium tetrafluoroborate, alcohols (e.g., methanol, ethanol, isopropanol, phenoxyethanol), sodium nitrate, and borid acid / sodium borate; disinfectants such as phenol, phenolic derivates (e.g., salicylic acid, sodium pentachlorophenate, thymol, 4-chloro-3-methylphenol, 1,4-dichlorobenzen, chinosol/oxyquinoline, quaternary ammonium compounds) benzalkonium chloride, tetradecylamine, polyhexamethylene guanidine hydrochloride; and varied other buffers, humectants, wetting-solutions, softeners, anticoagulants, and salts. Of course, the aforementioned chemicals and compounds have varied properties and, in practice, are used in varied amounts and proportions. Moreover, there is no established standard embalming method that has been espoused by the anatomical community. Therefore, different anatomy laboratories, possessing diverse chemical milieux, are each likely face unique challenges with ventilation and maintaining healthy air-quality. This study assessed only formalin / airborne formaldehyde. Other chemicals may prove more difficult to exhaust; although, by creating a current of air flow away from the face of the dissector, it would seem likely that local exhaust ventilation systems would help decrease levels of airborne embalming chemicals, in general.

While there are many chemicals utilized in embalming, formaldehyde is utilized around the world and remains one of the most common materials utilized in embalming [2,4,16]. Further, formaldehyde has recently been reclassified as a carcinogen [3,4,17]. Furthermore, formaldehyde exposure is particularly dangerous for vulnerable populations including those who are pregnant [18]. Embalming fluids often contain some fraction of formaldehyde; however, they are not composed of 37% formaldehyde, as was utilized in these experiments. Indeed, in the control experiment, airborne formaldehyde levels rose to 5.0ppm within only a minute— two-and-a-half times the OSHA STEL of 2.0ppm (Fig. 3C). This study, therefore, tested an unrealistically high concentration of formaldehyde. Still, the ventilation system using all four fans left no trace of airborne formaldehyde.

While the LEV system that produced 761cfm of exhaust flow reduced formaldehyde levels below the NIOSH TWA of 0.016ppm, it was the only prototype that was capable of doing so, at least when the formalin pool was 8in above the table. While seemingly intuitive, it must be noted that the farther away from the downdraft table a fixed tissue is located, the more likely airborne chemicals will be liberated into the environment and, therefore, the greater the demand for strong exhaust.

The cost of materials used to build the nine local exhaust ventilation systems tested in this study included $250 (USD) for the two 12-inch duct fans ($125/fan); $120 for the two 6-inch duct fans ($60/fan); $58 for the two wall vent outlets ($29/outlet); $71 for the wye branches ($53 for the 12-inch wye branch and $18 for the 6-inch wye branch); $62 for the two duct reducers ($31/reducer); $30 for 25ft of 12-inch ducting; $24 for 25ft of 6-inch ducting; and ~$30 for gear-adjustable clamps and duct tape. The total cost of materials amounted to $645. However, if one were to only build the “I” configuration LEV system, which exhausted 761cfm and left no detectable airborne formaldehyde, it would not require the 12-inch wye, 6-inch take-offs, nor as much ducting / duct clamps and would, therefore, cost less than $600.

Series, Parallel, or Series-Parallel: Pros and Cons of Varied Fan Arrangements:

Fans arranged in series generate more air flow in a high-resistance setting relative to fans arranged in parallel. However, in a low-resistance setting, fans arranged in parallel will produce more air flow than they would if they were arranged in series. A series-parallel arrangement of fans shares qualities with both series and parallel arrangements and may be useful when a large amount of airflow is desired in spite of high-resistance. This study shows prototypes with fans arranged in series, parallel, and in series-parallel. The “I” arrangement of fans (series-parallel fan arrangement) created the best exhaust from the dissection table. Indeed, the negative pressure generated by the “I” arrangement created mild difficulty opening the hinged covers due to the suction it produced. By contrast, other arrangements (e.g., the “A” arrangement) created minimal difficulty in opening the closed table. Hence, different exhaust flow and negative pressure will be created by different combinations of fans based upon size, power, and arrangement. The desired amount of airflow and the capacity to overcome the resistance generated by ducting and the downdraft table should be kept in mind while designing LEV systems.

An LEV system can incorporate a chemical adsorption filter in order to capture embalming vapors [19]. A chemical adsorption filter can decrease output of VOCs from an exhaust system; however, at the same time, it can increase resistance and thus decrease exhaust flow and removal of VOCs from the breathing area above the downdraft table. Therefore, if a chemical adsorption filter were to be utilized in conjunction with a local ventilation system, the system would have to have the capacity to generate adequate exhaust flow from the downdraft table in spite of the added resistance imposed by the chemical adsorption device. Further, a chemical absorption device that vents clean air back into a dissection room would need to be maintained or changed regularly; otherwise, it could vent VOCs into the same area from which the VOCs are trying to be removed.

Could other systems exhaust fumes effectively and cost less? Introducing a Novel Exhaust System:

Based upon the nine LEV systems introduced thus far in this report, another exhaust system was subsequently designed, built, and tested. The system incorporated three 6-inch wye connectors, four 6-inch duct fans in parallel mounted to plastic shelving, heavy-duty 6-inch ducting, and four 6-inch bull-nosed external extractor wall vent outlets. The LEV system can be seen in Figure 4 alongside a compact version of the “I” ventilation system. The new system was tested as per the protocols identified in the Materials and Methods of this report. The system created an exhaust of 777cfm with all fans set to high speed (603cfm with all fans set to low speed), allowed no detectable airborne formaldehyde (0ppm) despite utilizing a 1000mL pool of formalin (consisting of 37% formaldehyde) positioned directly beneath a formaldehyde-meter, and operated at a very low noise level (maximum of 69.2dBA directly above the table with coexisting baseline room noise of 38.6dBA; 63.5dBA alongside the table). Furthermore, the exhaust system cost less than $400 (USD), was assembled in a matter of minutes, and required minimal know-how to build. The only tools required were a screwdriver, scissors, and cutting pliers. Further, there were no heavy parts (the heaviest item was the 6-inch fan = 4.7kg (10.35lb)) and it took only one individual to assemble.

Figure. 4:

Figure. 4:

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Novel local ventilation systems capable of effectively eliminating airborne formaldehyde levels. A: An exhaust system capable of quietly exhausting 777cfm. The system consists of 3ft of 6in diameter duct > 6in X 6in X 6in wye connector > two 6in X 6in X 6in wye connectors > four ~1.5 – 2ft long 6in diameter ducts running in parallel > four 6-inch fans in parallel > four 2ft long 6in diameter ducts in parallel > four external wall vents. B: A modification to the “I” exhaust system capable of exhausting 761cfm. The system consists of 3ft of 6in diameter duct > 6i n X 6in X 6in wye connector > two 6inch fans in parallel > two 1ft long 6in diameter ducts in parallel > two 12in to 6in reducers in parallel > two 12inch fans in parallel > two 6in long 12in diameter ducts in parallel > two external wall vents.

A comparison between the exhaust of the “777” system and the “I” system (Fig. 4) was performed by holding the anemometer to the slotted exhaust openings on the downdraft table. Both systems created identical exhaust flow at the table surface. To assess how the LEV systems performed under a challenge of increased resistance to flow, a 6-inch-to-4-inch reducer was affixed to the terminal 6-inch wye and air flow was assessed at the 4-inch opening. Airflow from the “777” system decreased to 402cfm (48% drop) whereas airflow from the “I” system decreased to 516cfm (32% drop). Therefore, the “I” system was able to produce greater flow under higher resistance. Indeed, the result was expected since, as mentioned earlier, fans arranged in series create more flow under higher resistance while fans in parallel create more flow under low resistance settings. With regard to sound production, the noise between the two tables with both prototypes operating at high speed was 63.7dBA― essentially the same as standing alongside an individual downdraft table.

The LEV systems tested in this study were independent of any other source of negative pressure (e.g., building exhaust ventilation) as other LEV systems have been described previously [19–23]. In fact, the LEV systems overcame a source of positive pressure from the outside environment. If the novel systems were affixed to pre-existing laboratory exhaust ducting, there would likely be a greater exhaust flow (i.e., >777cfm). Recently, the author reported the utilization of a retrofitted fume hood paired with a 6-inch inline duct fan: The flow of air from the retrofitted fume hood measured 305cfm. The inline duct fan alone produced a flow of 363cfm. Together, the fume hood and the duct fan produced a 471cfm exhaust [8]. Parenthetically, the 471cfm exhaust was capable of effectively eliminating airborne volatile organic compounds emanating from a cadaver that had been recently embalmed with Carolina’s Perfect Solution® Concentrate with Phenol (Carolina Biological Supply Company, Burlington, NC) [8]. Also, Klein et al. [24] reported success in controlling formaldehyde in a gross anatomy laboratory at Yale University with 275cfm of exhaust flow per downdraft table.

As aforementioned, a LEV exhaust eliminated airborne volatile organic compounds which included phenol [8]. It is important to note that phenol-embalmed cadavers may liberate flammable vapors [25]. Local exhaust ventilation systems remove potentially flammable vapors directly from their source of emanation, whereas general ventilation systems typically move potentially flammable vapors toward the floor of the room before being exhausted from the room. Therefore, LEV systems should be preferred to general laboratory whole-room ventilation systems with regard to rapid elimination of vapors that are potentially flammable.

This manuscript has been composed in the setting of a pandemic, namely that of COVID-19, a disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The SARS-CoV-2 pathogen may be transmitted by aerosol [26–29]. In the light of this pandemic, it should be noted that respiratory droplets or aerosol containing any type of pathogen (not exclusive to SARS-CoV-2) may be influenced by air currents. Accordingly, utilization of LEV systems may aid in limiting the spread of infection by encouraging downdraft and elimination of aerosolized pathogens. The aforementioned point is particularly important in a gross anatomy laboratory setting where close person-to-person contact is common and optimal social distancing is difficult.

The LEV systems shown in this report required no modification of existing building infrastructure. The LEV systems only required an open window. Thus, these systems can avoid unnecessarily modifying buildings. However, when determining where to locate the LEV, appropriate consideration should be taken to eliminate risk of re-entrainment of vapors into the building ventilation system. Likewise, consideration should be taken to eliminate risk of exposure to pedestrians outside of the building.

With regard to ventilation, Goldman [30] emphasized the fortuitous circumstance of creating a gross anatomy laboratory on the top floor of a building at Philadelphia University. This author shared similar views with the creation of a gross anatomy laboratory at West Liberty University [8]. Indeed, building modifications and upgrades to air handling systems in order to accommodate for a gross anatomy laboratory can cost hundreds of thousands of dollars [31]. Yet, the LEV systems described in this report make such structural considerations practically moot. They also allow for dissection laboratory to be mobile and dynamic with regard to temporal and spatial changes― the capacity to breakdown, move, and rebuild the LEV systems with ease.

Limitations to the Study:

The experiments performed in this study were done in a controlled environment and, therefore, are not representative of an active laboratory environment. An active laboratory environment includes individuals walking past dissection tables, thus creating their own drafts which would influence airborne chemical movement. Also, this study measured the noise produced by only two simultaneously active prototypes. While the noise generated by each individual system was quiet, the simultaneous utilization of multiple exhaust systems might increase noise levels, especially when operating at the same time as an active laboratory environment; this scenario was not assessed by this study. Also, this study utilized only one model of downdraft table; therefore, results may vary when the LEV systems are used on other downdraft table models. Additionally, this study only assessed two brands/models of inline duct fans. There are many brands, models, and sizes of inline duct fans. Some can create high air flow despite being subject to high static pressure, whereas others create very low flow even when subject to minimal static pressure. Further, some fans are designed to be particularly quite at the sacrifice of air flow. Thus, different inline duct fans will produce different air flow, airborne chemical removal, and noise. Further study should assess similar LEV systems using different fans in different environments and at different scales.

Conclusion:

An inability to exhaust harmful fumes is an impediment to gross anatomical education. Overcoming this hurdle will facilitate gross anatomical education. This study identifies simple and inexpensive LEV systems that utilize in-line duct fans to create healthy and quiet exhaust flow. The exhaust systems can be assembled rapidly and with little know-how. This information marks an improvement in laboratory safety measures, facilitates the creation of gross anatomy laboratories, and improves access to gross anatomical education.

Highlights:

  • Explains how to build local exhaust ventilation systems from a gross anatomy laboratory.

  • Details local exhaust ventilation systems that are effective, easy-to-build, and inexpensive.

  • Results mark improvements in laboratory safety and improves access to gross anatomy education.

Acknowledgements:

The work was made possible through funding from the West Virginia IDeA Network for Biomedical Research Excellence [P20GM103434] and NIH-NIAID [5K22AI087703]. The author declares no conflicts-of-interest.

Footnotes

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