Presentation on theme: "Frank R. Demer, MS, CIH, CSP University of Arizona, Tucson, AZ 85721"— Presentation transcript:
1Frank R. Demer, MS, CIH, CSP University of Arizona, Tucson, AZ 85721 Engineering Controls to Reduce Formaldehyde Exposures: What works, what doesn’t, and why?Frank R. Demer, MS, CIH, CSPUniversity of Arizona, Tucson, AZ 85721My name is Frank Demer. I’m a Health and Safety Officer at the University of Arizona where I have worked for 23 years.In my tenure at the UA, I’ve been involved in the occupational (or industrial) hygiene evaluation and review of a number of gross anatomy laboratories including: the 1995 remodel and expansion of our College of Medicine’s lab in Tucson; our new College of Medicine’s lab in Phoenix - which is in final phases of construction - and other smaller labs in between.The title of my talk today is: Engineering Controls to Reduce Formaldehyde Exposures: What works, what doesn’t, and why?My goals are to:1) share some of what I’ve learned from my gross anatomy lab experience, and2) help you become conversant with basic anatomy lab ventilation concepts and approaches to better advocate for effective lab design, maintenance and operation at your institution.
2Gross Anatomy - The problem All projects usually begin with identification of problem to be solvedAs with most projects, I’d like to begin by first defining the problem, which is important when you are communicating with those who may not be so familiar with the issues of concern (e.g. architects, engineers, administrators).Gross Anatomy - The problem
3The Problem Preserved donors needed for extended dissection against decomposition, microbial contamination, desiccationTraditional preservations method include formaldehydeirritant, sensitizing gas and known human carcinogenvery low OELClose access to donors required, without significant formaldehyde exposure, in teaching environmentexposure primarily by inhalation and also skin contactrelative quite required for communicationThe problem in the gross anatomy environment can be summarized as follows:1) preserved donors are needed for extended dissection;2) traditional preservation methods include formaldehyde, and3) close access to donors is required - without significant formaldehyde exposure - in a teaching environment.The primary route of exposure to formaldehyde in these environments is by inhalation and that’s the main problem I would like to address - along with some ancillary issues.
4Hierarchy of Exposure Controls Elimination/SubstitutionProcess ModificationEngineering ControlsAdministrative ControlsPersonal ProtectionThe hierarchy of exposure controls is shown here. This is the order in which hazard controls should be applied – starting at the hazard source – and working your way down the list as necessary to control the hazards.While the first two controls in the hierarchy are worthy controls to pursue - currently available controls by these methods do not completely replace traditional anatomy teaching techniques, or are not developed to the point where formaldehyde can be completely eliminated from the donor preservation process.Therefore - engineered ventilation controls continue to be the most critical aspect of formaldehyde control in a gross anatomy lab environment.
5ACGIH Industrial Ventilation – A Manual of Recommended Practices (1951 - 2010) In occupational (or industrial) hygiene, the “gold standard” of engineered ventilation controls (at least in the US) is the Industrial Ventilation Manual, from the American Conference of Governmental Industrial Hygienists. This Manual has been in publication since 1951 – for over 60 years - and is in its 27th edition.I would like to apply the proven, established principles in this manual to formaldehyde control in the gross anatomy environment and compare the assortment of engineering methods that have been employed and described by numerous investigators with varying degrees of success.I will refer to this publication for the remainder of my presentation as “The Manual.”Engineered ventilation controls – Applying proven established principles
6Bibliography of Articles on Formaldehyde American Association of Anatomists websiteBecause of time, my presentation is mostly void of study references and details. I will instead focus on basic concepts supported by these references and my experience.For details, I recommend that you refer to a bibliography of articles on formaldehyde, which is posted on the American Association of Anatomists website.
7Engineered Ventilation Controls Dilution “General” ventilationDilution of contaminated air with uncontaminated airLocal exhaustCaptures contaminants at generation point(s) and remove from workplace through duct systemThe two categories of engineered ventilation control are dilution or “general” ventilation and local exhaust.The easiest engineered ventilation control to apply is dilution ventilation where the contaminant is diluted with uncontaminated air – hopefully to a safe level - so let’s first look at dilution ventilation with respect to this problem.
8Dilution Ventilation Criteria (per ACGIH Vent. Manual) Toxicity of contaminant must be lowTypically used to control organic liquids with OELs >100 ppmPeople must be far enough away from source ORGeneration of contaminant must be in low concentrations so that workers will not have exposures >OELContaminant generation must not be too great or dilution airflow rate will be impracticalGeneration of contaminants must be reasonably uniform“The Manual” defines criteria for determining if dilution ventilation is applicable for a particular application and the gross anatomy environment fails on almost all counts.1) The toxicity of formaldehyde is significant;2) people are close to the source;3) where exposures are above occupational exposure limits, and4) the amount of dilution air required to reduce exposures below these limits is impractical.
9Dilution Ventilation Alone is Inadequate Therefore – dilution ventilation - by itself - is inadequate as a formaldehyde exposure control in gross anatomy and exposures in these environments inevitably exceed occupational exposure limits. Unfortunately, this is the primary control employed in most gross anatomy labs.
10Dilution Ventilation as Supplemental Control However – dilution ventilation can be useful as a supplemental control – especially if applied appropriately.A poor application of dilution ventilation introduces clean air across the contaminant source, through the breathing zone of the worker and out the exhaust – exposing the worker and short circuiting most of the workspace.The best application introduces clean air from one side of the workspace, through the worker, then through the contaminant source and out the exhaust.
11Dilution Ventilation Maximized By: Lowering ceiling to reduce room volumeIntroducing and exhausting air in a top to bottom “plug” fashionTo increase effective room air exchangesIn gross anatomy labs, dilution ventilation as a supplemental control can be maximized by:1) lowering the ceiling to reduce the room volume, and2) introducing and exhausting air in a top to bottom “plug” fashion – both to increase effective room air exchanges.
12Lowering Ceiling 9 ft (2.7 m) Here is a before and after lab remodel in which this was done – going from a 13½ ft ceiling to 9 ft ceiling.
13Top to Bottom “Plug” Airflow So ideally, you want to supply clean air through the ceiling and exhaust contaminated air through the floor or below the anatomist – not because formaldehyde is significantly heavier than air (a common misconception) - but because you want clean air to flow through the breathing zone of the anatomist, then through the contaminant source and out the exhaust.
14Is Formaldehyde Heavier Than Air? Specific density of formaldehyde gas = (air = 1)Specific density of 10 ppm formaldehyde in air =(10 ppm x 1.067) + (999,990 ppm x 1) =1,000,000 ppmLow ppm formaldehyde-contaminated air does not sink– it diffuses in all directions and moves with air currentsBefore I proceed, let me answer the question – Is formaldehyde heavier than air?Pure formaldehyde gas is times heavier than air but low ppm formaldehyde-contaminated air, like that found in a gross anatomy environment - even at its worst - is not significantly heavier than clean air.Contaminated air in these environments does not sink but rather diffuses in all directions and moves with air currents.
15Top to Bottom “Plug” Airflow Local ExhaustTo maximize dilution ventilation, the goal is to supply clean air through the ceiling and exhaust it below the anatomist’s breathing zone.Ideally, exhaust it at the contaminant source – the donor - and remove it through a duct system. This we call “local exhaust.”This diagram shows the general idea and these video clips visualize the concept using a fog machine.
16Local Exhaust Hood Design Principles (per ACGIH Vent. Manual) Minimize all opposing air motion about the processEnclose operation as much as possible“The Manual” defines basic principles for local exhaust design and these can be applied to the gross anatomy lab.First – minimize all opposing air motion about the process. Second – enclose the operation as much as possible – while still allowing necessary access.
17Local Exhaust Hood Design Principles (per ACGIH Vent. Manual) Minimize all opposing air motion about the processEnclose operation as much as possiblePlace hood as close to source as possibleThird - place the hood as close to the sources as possible – to minimize the amount of exhaust required and maximize hood capture.
18Local Exhaust Hood Design Principles (per ACGIH Vent. Manual) Minimize all opposing air motion about the processEnclose operation as much as possiblePlace hood as close to source as possibleLocate hood so contaminant is removed away from breathing zone of userFourth - locate the hood so contaminant is removed away from the breathing zone of the user – not through it.
19Local Exhaust Hood Design Principles (per ACGIH Vent. Manual) Minimize all opposing air motion about the processEnclose operation as much as possiblePlace hood as close to source as possibleLocate hood so contaminant is removed away from breathing zone of userCreate air flow past source sufficient to capture contaminant in hoodLastly - create air flow past the source sufficient to capture the contaminant in the hood. These are the principles of local exhaust design.Now let’s look at some of the various types of local exhaust designs that have been applied to the gross anatomy lab and consider their effectiveness in controlling formaldehyde inhalation exposure.
20Local Exhaust Enclosing hoods Included is the enclosing hood design where the contaminant source is inside the exhaust hood.
21Enclosing Hood Anatomy Table Here is a successful example of this design in gross anatomy with the enclosing hood structure created by flexible foam sides to allow donor access by the anatomist.As you can see, the donor is enclosed by the flexible sides.
22Local Exhaust Enclosing hoods Capturing hoods Another type of local exhaust design is the capturing hood, which does not enclose the source but instead relies on a flow of air into the hood opening to carry the contaminated air into the hood.
23Local Exhaust Plain opening capture hood Slotted capture hood Enclosing hoodsCapturing hoodsPlain openingSlot hoodTo force uniformity of air flow across, and along length, of slotsPlenum cross-sectional area must be > 2 times slot areaThe simplest form of this design is the plain opening capture hood but these hoods have greater suction closer to the exhaust duct.Adding slots to the plain hood makes a slot capture hood, which forces uniformity of air flow across, and along the length, of the slots.But in order for the slot hood to work like this, the plenum cross-sectional area (shown in blue) must be greater than 2 times the slot area (shown in red).“The Manual” includes a section of successful local exhaust designs for specific operations. Included in this section are several slot hood designs that are applicable to the gross anatomy lab.
24Side Slot Mortuary Table (per ACGIH Vent. Manual) There is the side slot mortuary table design, with exhaust on both long sides of the table. This design is one of the more recent additions to “The Manual.”
25Undersized Side Slot Plenum Too much flex ductHere is an adaptation of this design but unfortunately, the plenum is not appropriately sized for the slots so the far side of the slots will have less exhaust. Also, there is an issue with excess flexible duct. I’ll mention this more later.
26Side Slot Table (per ACGIH Vent. Manual) “The Manual” also has a generic side slot table design. Being that it has an appropriately-sized plenum, it will have equal suction all along the slots.
27Perimeter Slot Anatomy Table Here is a successful adaptation of this design in gross anatomy with the slot extending around the entire perimeter of the table. However – this table is too wide for ergonomic reasons, which I mention more about later.Table too wide
28Solvent Degreasing Tank Side Slot Ventilation (per ACGIH Vent. Manual) “The Manual” also has a solvent degreasing tank side slot ventilation design, which adapts well to the gross anatomy lab. Instead of a tank, you design for an anatomy table. It also has an appropriately sized plenum which provides equal suction all along the slots.
29Solvent Degreasing Tank Ventilation w/ Side Slots and Sloping Plenum (per ACGIH Vent. Manual) A variation of this design is also in “The Manual” – instead of a straight plenum, it has a sloping plenum.The plenum in this design is only as large as it needs to be at any point along the slot length to provide equal suction all along the slots.
30Side Slot Anatomy Station and Table w/ Sloping Plenum Here are a couple successful adaptations of these designs in gross anatomy – except the duct size is too small. I’ll mention more on this later.One of the designs is a table with side exhaust slots - the other is a side slot exhaust station that accepts a standard anatomy table.Ducts too small
31Side Slot Anatomy Table Station w/ Sloping Plenum Here are a couple other similar side slot exhaust station designs.
32Side Slot Embalming Table w/ Sloping Plenum And a successful, commercially available adaptation of the design to an embalming table.
33Local Exhaust Enclosing hoods Capturing hoods Slot hood Downdraft hood Another capture hood design is the downdraft hood, where the table top has exhaust holes or slots in it and air is sucked into the plenum underneath.The problem with this design, as applied to gross anatomy, is the donor blocks some of the exhaust openings – and, to keep the donor from desiccating, it is wrapped in plastic, which further blocks the exhaust - limiting the hoods effectiveness.Therefore, this design is not recommended.
34Downdraft Anatomy Tables Unfortunately, the majority, of commercially available exhausted anatomy tables come with this downdraft design.
35Local Exhaust Enclosing hoods Capturing hoods Receiving hoods Another type of local exhaust design is the receiving hood, which is a capture hood that is positioned so that gas and vapor contaminants are lifted by convection, or other directional air movement, towards the hood opening.
36Local Exhaust Enclosing hoods Capturing hoods Receiving hoods Canopy hoodThey are typically used as a canopy to receive contaminants mixed with heated air and are an inappropriate design for the gross anatomy because the process is not heated and the anatomist would be inappropriately positioned between the contaminant source and the hood.
37Canopy Hood Over Embalming Table Although, you will find this design used.
38Local Exhaust Enclosing hoods Capturing hoods Receiving hoods Canopy hoodPush-pull hoodAnother type of receiving hood is a push-pull hood, where clean air is discharged or “pushed” at one side of the hood and exhausted or “pulled” at the other side.
39Local Exhaust Enclosing hoods Capturing hoods Receiving hoods Canopy hoodPush-pull hoodAirflow obstructions are a significant problem with these hoods. In a gross anatomy lab the donor and the anatomists are significant, problematic obstructions.
40Local Exhaust Enclosing hoods Capturing hoods Receiving hoods Canopy hoodPush-pull hoodAlso, even without obstructions, push-pull air balance is very tricky. For these reasons, this design is not recommended for gross anatomy - although, it has been tried.
41Push-Pull Hood Anatomy Table RecirculatingHere is one such design. This particular push-pull design also includes an air cleaning feature, which allows for recirculation of cleaned air back into the lab.
42Engineered Ventilation Controls Dilution ventilationLocal exhaustEnclosing hoods \Capturing hoods } Recirculating or 100% exhaustReceiving hoods /This recirculation feature can be applied to all the designs discussed.
43Recirculating Side Slot Table Formaldehyde filtering media - expensive, requires frequent changingReliable and sensitive monitoring system required to detect filter breakthroughNoisy w/ significant room air turbulenceNot IdealIt has been successfully applied to the side slot exhaust table design. Here are two versions with one more successful than the other.Each has problematic design issues, some of which I’ve mentioned already or will mention more on later.Recirculating designs can work but:1) the filter media is expensive and requires frequent changing;2) a monitoring system is required to detect filter breakthrough, and3) noise and room air turbulence are issues - because the fan and air discharge is in the room.For these reasons recirculating designs are not ideal.“Unfriendly“ wide edgeDuct too small – too much flex duct – plenum too small
44Recirculating Downdraft Table Here is it applied to the downdraft table design, which I’ve already mentioned, is not a recommended design.
45100% Exhaust Preferred to exhaust to outside 5-10% less make-up air than exhaust to keep room negative in pressureNote - recirculating side slot table will require some general exhaust(5 – 10% of supply) to keep lab negative in pressure to surrounding areasAir flow sufficient to adequately capture formaldehydeSo – 100% exhaust to the outside is preferred;with 5-10% more exhaust than supply to keep the room negative in pressure to surrounding areas – to prevent the spread of formaldehyde contaminated air, andsufficient airflow to adequately capture the formaldehyde in the enclosed or side slot exhaust hood.
46Effective Zone of Hood Capture Airflow is what defines the effective zone of hood capture - and this zone - even with adequate airflow - is relatively small.
47Blowing vs. ExhaustingAt one diameter away from an exhaust opening, the air velocity drops to 10%. In contrast, when the same volume of air is blown through a similarly-sized opening, the air travels 30 diameters before its velocity drops to 10%.
48Effective Capture Zone - Capture Velocity or Proper Volume (per ACGIH Vent. Manual) Conditions ofContaminantDispersionReleased with practically novelocity into quite air(e.g., evaporation)ft/min cfm/ft ( m/s) ( m3s/m2)Large hoods- Large air massmoving into hood- Contaminant underSmall Hoods influence of hood forlonger time- More dilution due toaboveWhen a contaminant is released with practically no velocity into quite air, like formaldehyde is in gross anatomy, “The Manual” recommends a capture velocity of 75–100 fpm to transport the contaminant into the hood. This recommendation applies to smaller hoods.With large hoods, like an exhausted anatomy table, because of the larger mass of air moving into the hood and as a result, greater contaminant dilution, the recommendation is converted to a proper volume of cfm/ft2 of exhausted area.
49Proper Exhaust Volume - Anatomy Table ~16 ft2 (~1.5 m2) table area at 50 – 100 cfm/ft2 ( m3s/m2)800 – 1600 cfm (0.38 – 0.76 m3/s) per tableFor a standard gross anatomy table with a 16ft2 table top, this translates to a recommended airflow of between cfm per table.
50Tracer Gas Testing Hood Capture Efficiency = as-used tracer gas capture conc. / 100% tracer gas capture conc.100% tracer gas capture concentration(measured in duct)as-used tracer gas capture concentration(measured in duct)Using a tracer gas (e.g., sulfur hexafluoride) to simulate formaldehyde emitted from a donor, this range can be further defined.
51Proper Exhaust Volume – Anatomy Table (tracer gas testing by NIOSH and University of Arizona) 700 – 1600 cfm (0.33 – 0.76 m3/s) per tableLowest end of range only applicable with ideal conditionsTracer gas testing of the side slot exhaust table design by two independent research groups concluded that the recommend airflow range could be safely extended to as low as 700 cfm, where the capture efficiency is still 95%. However, the lowest end of this airflow range is only applicable with ideal conditions.
52Factors Affecting Choice Within Hood Flow Range 700 – 1600 cfm (0 Factors Affecting Choice Within Hood Flow Range 700 – 1600 cfm (0.33 – 0.76 m3/s) per tableLower End of Range (700 cfm)Upper End of Range (1600 cfm)Large hood – large air mass in motionContaminants of low toxicityIntermittent, low productionMinimal room air currentsUse of table top, flanges and bafflesUnobstructed airflow into hoodSmall hood - local control onlyContaminants of high toxicityHigh production, heavy useDisturbing room air currentsFree standing hoodObjects and surfaces that impede air flow into hoodSo … cfm/table is quite a range. To help narrow down the airflow choice “The Manual” defines a list of factors to consider.In gross anatomy, we are dealing with a large hood; the toxicity of the contaminant (i.e., formaldehyde) is significant, and the table use is intermittent.Considering the first three factors on the list, neither end of the range is strongly favored over the other.But the last three factors on this list – room air currents, air channeling features and airflow obstructions – can greatly influence the airflow choice. Of these three factors, room air currents is probably the most important.
53Effects of Cross Drafts High velocity room air currents can create cross drafts that interfere with effective hood capture.
54Make-Up (Replacement) Air Exhaust air from hood (air out) = Make up air to hood (air in)V = Q/A, Air velocity (V) = air flow (Q) / area (A)Make-up air to hoodThe most significant cross draft is the make-up (or replacement) air for the hood.Ignoring the 5-10% negative offset in make-up air to keep the lab negative in pressure - exhaust air from the hood has to more-or-less equal supply air to the hood – air out has to more-or-less equal air in.The velocity of the make-up air is equal to the airflow divided by the area of the make-up air diffuser.Since airflow is constant – to reduce the make-up air velocity, it is necessary to increase the area of the make-up air diffuser.Exhaust air from hood
55Make-Up Air (Replacement Air) Exhaust air from hood (air out) = Make up air to hood (air in)V = Q/A, Air velocity (V) = air flow (Q) / area (A)Release make-up air above table, over large area in direction of exhaust (goal is <25% capture velocity)>24 ft2 (>2.3 m2) make-up air area (3, 2’ x 4’ ceilings tiles)Ideally, you want to release make-up air above the table, over a large area, in the direction of exhaust.The goal is to reduce the make-up air velocity to less than 25% capture velocity.This translates to a supply air diffuser area greater than 24 ft2 or three 2’ x 4’ ceilings tiles equivalents of area.
56Make-Up Air (Replacement Air) Preferred Avoid(large, laminar flow diffuser above table) (small, directional diffusers)On the left is the preferred means of doing this - large, laminar flow diffuser above the table. On the right is what you want to avoid - small, directional diffusers.
57Table Tops, Flanges and Baffles Plain openingOther significant influences of hood airflow choice are air channeling features. Plain opening hoods exhaust air from all directions.
58Table Tops, Flanges and Baffles Plain openingTable topTable tops - like the anatomy table -
59Table Tops, Flanges and Baffles Plain openingFlangeflanges and
60Table Tops, Flanges and Baffles Plain openingBafflebaffles can be used to channel more airflow over the contaminant source and reduce the required airflow necessary for contaminant capture
61Table Tops, Flanges and Baffles Channel more airflow over source reducing required airflow (flanges by as much as 25%)Plain openingBaffled slot hood Hood on table Flanged slot- flanges can reduce the required airflow by as much as 25%.
62Flanged and Baffled Slot Tables Flanged slot on tableHere are examples of flanged and baffled slot exhaust anatomy tables where more airflow is channeled over the formaldehyde source – the donor.Baffled slot on table
63Airflow Obstructions Preferred Avoid (tight plastic sheeting that lies flat) (loose plastic sheeting)Lastly airflow obstructions are another important factor to consider – the biggest concern being the plastic used to retard donor desiccation.On the left is the preferred means of avoiding this - tight plastic sheeting that lies flat and is only opened to access the portion of the donor being used.On the right is what you want to avoid - loose plastic sheeting that blocks the slots. If the slots get blocked, the system doesn’t work.
64Factors Affecting Choice Within Hood Flow Range Lower End of Range (700 cfm)Upper End of Range (1600 cfm)Large hood – large air mass in motionContaminants of low toxicityIntermittent, low productionMinimal room air currentsUse of table top, flanges and bafflesUnobstructed airflow into hoodSmall hood - local control onlyContaminants of high toxicityHigh production, heavy useDisturbing room air currentsFree standing hoodObjects and surfaces that impede air flow into hoodIf the previously mention factors can be satisfactorily addressed, it is not unreasonable to design enclosed or side slot exhaust tables with airflows between 900 and 1200 cfm and still have an adequate margin of safety.900 – 1200 cfm (0.42 – 0.57 m3/s) per table
65Duct Design Issues Air turbulence = noise Remember - the gross anatomy lab is a teaching environmentAir turbulence, friction and high air speed = moneyThe harder it is to move air - the greater capital equipment/operating costsA couple general comments on duct design – Air turbulence = noiseRemember – the gross anatomy lab is a teaching environment – andair turbulence, friction and high air speed = money.The harder it is to move air - the greater the capital equipment/operating costs
66Duct Design IssuesSmooth round duct preferred over rectangular or flex duct(< friction & turbulence, > structural integrity)Rectangular duct only when space requirements preclude round – as square as possible (< resistance)Use non-collapseable flex duct only where necessary and as little as possible (<2 ft)Avoid abrupt changes in duct direction and size when possibleSmooth round ducts are preferred.Only use rectangular and flex duct where necessary and as little as possible and avoid abrupt changes in duct direction and size when possible.
67Duct Design Preferred Avoid Excessive flex duct On the left is the preferred means of minimizing air turbulence and friction.Duct work should ideally look like freeways where imaginary miniature cars can smoothly drive through.On the right is what you want to avoid. Flexible duct is like a windy, bumpy road - using the freeway analogy.
68Duct Design Preferred Avoid On the left are examples of preferred ductwork configurations – minimal flex duct with a purpose and aerodynamic transitions.On the right are examples of what you want to avoid – excessive flex duct, rectangular duct, abrupt changes in duct direction and size.
69Economics1000 – 2000 fpm (5.1 – 10.2 m/s) is economic optimum duct velocity for gases and vapors8 – 16 in round duct (0.20 – 0.41 m) for 700 – 1600 cfm (0.33 – 0.76 m3/s)12 in round duct (0.30 m) for 900 – 1200 cfm (0.42 – 0.57 m3/s)1 fume hood (equivalent to side slot exhaust table) represents energy equivalents of 3.5 households in same climate (EPA estimate)Consider “In use” and “Not in use” modes and performance indicatorsIncorporate existing equipment where possibleWith regards to economic issues –2000 fpm is the economic optimum duct velocity.Remember - high air speed = money. Extremely low air speeds require too much duct space.This range is a happy medium.Listed here are appropriate duct size ranges if all a table’s exhaust air goes through one duct.Most commercially available exhausted table designs come with duct connections that are too small - 6 inches.In addition, side slot exhaust tables represents the energy equivalents of 3.5 households in same climate so it is important to consider “In use” and “Not in use” modes and have performance indicators –because tables need much less exhaust airflow when the donor is in a sealed bag and not being used as it is for most of the time.It is also important to incorporate existing equipment where possible when remodeling labs because lab equipment and furniture is extremely expensive.
70“Not in use” Mode300 – 600 cfm (0.14 – m3/s), field verified by authorBelieved to be very conservativeA “Not in use” ventilation range of between 300 – 600 cfm per table is believed to be a very conservative recommendation, based on tracer gas and field testing.
71Performance Indicators A simple performance indicator is a magnehelic gauge. Each table should have something like this and simple instructions to let the user know if the table exhaust is working adequately.
72Using Existing Equipment Here are two ways of utilizing existing equipment – modify standard anatomy tables to have side slot exhaust and plenum or use standard anatomy tables in a side slot exhaust station.Ducts too small
73ErgonomicsDesign for comfortable user posture - Ideally adjustable heightSpecimen at standing elbow height, 37 – 44 in (0.94 – 1.12 m), if not adjustable, work at upper range and use step stoolsStanding foot rail at 6 in (0.15 m), 1 in (0.254 cm) diameter rodMinimize reach distance by keeping side slot plenums narrowAvoid “unfriendly” edges (e.g., contact stresses)Consider ease of cleaningMock-up or prototype is highly recommendedWith regards to ergonomics considerations - design for comfortable user posture – Ideally tables should be adjustable in height.Some recommended table height ranges are listed here.Consider a standing foot rail and narrow side slot plenum to minimize reach distances and reduce back strain.Avoid “unfriendly” edges (or contact stresses) and consider ease of cleaning.Mock-ups or prototypes are highly recommended for working out these ergonomic issues in the design phase.
74Ergonomics Preferred Avoid On the left are examples of preferred ergonomic features – height adjustable, narrow table width, rounded edges.On the right are examples of what you want to avoid – tall table heights, unfriendly edges, wide tables, bulky table covers.
75Summary recommendations Engineering Controls to Reduce Formaldehyde Exposures in AnatomyIn conclusion, the following summarizes my recommendations with regards to engineered ventilation controls for formaldehyde exposure a gross anatomy lab environment.Summary recommendations
76Summary Recommendations Reduce ceiling height, if possible - 9 ft (2.7 m)Flanged, side slot exhaust table/station design with appropriately-sized plenum100% exhaust with 5 – 10 % less make-up air to keep room negative in pressure“On” mode: 900 – 1200 cfm (0.42 – 0.57 m3/s) depending on lab conditions“Off” mode: cfm (0.14 – 0.28 m3/s), very possibly less, with specimen sealed in plastic bag when not in useMake-up air through large laminar flow diffuser directly above table - >24 ft2 (>2.3 m2)1000 – 2000 fpm (5.1 – 10.2 m/s) duct velocity, round exhaust duct with < 2 ft (<0.6 m) flex duct and aerodynamic design features throughout, if possibleConsider ergonomics and economicsReduce the ceiling height, if possible - 9 ft is adequateUse the flanged, side slot exhaust table or station design with appropriately-sized plenumUse 100% exhaust with 5 – 10 % less make-up air to keep the lab negative in pressure with respect to surrounding areasDesign for an “On” mode airflow rate somewhere between 900 – 1200 cfm, depending on lab conditionsand an “Off” mode airflow rate somewhere between cfm, very possibly less - assuming the donor is well sealed in plastic bag when not in useProvide for make-up air through a large laminar flow diffuser directly above table – diffuser area should be 24 ft2 or greaterSize the ductwork for a 1000 – 2000 fpm duct velocity, use round exhaust duct and other aerodynamic features where possible - no more than 2 ft flex duct, if necessaryConsider ergonomics and economics
77Thank you for your attention Questions?/Comments Contact InformationPhone: (520)Thank you for your attention. Here is my contact information if you would like a copy of the presentation and text or would like to contact me for other reasons. If there is time, I’ll take questions or comments.