exposure risk of laboratory fume hoods · (aiha*), ansi/aiha z9.5-2012, laboratory ventilation...
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2019 IAQA Annual Meeting
Lawrence Meisenzahl
Vortex Hoods, LLC
Phone: 302-660-6516
Exposure Risk of Laboratory Fume Hoods
2019 IAQA Annual Meeting
Acknowledgements
In honored memory of Frank Fuller (deceased) and colleagues from DuPont: Barbara Dawson, Gee Joseph, Aaron Chen, John Rydzewski, Frank Olszewski, William Moye, Mark Mueller, Joseph Lala, John Fitzpatrick, colleagues at Delaware Engineering & Design Corp., Steve Krinsky, John Leslie, and at Pennoni Engineering, Robert Hayden, Bill Davison and Bob Opreska. The United States Patent number US 9,731,335 B2, Vortex Baffle for a Ventilated Enclosure, issued 8/15/2017, is for the design shown in Figure 3.
2019 IAQA Annual Meeting
References:
American Industrial Hygiene Association (AIHA*), ANSI/AIHA Z9.5-2012, Laboratory Ventilation
American Conference of Governmental Industrial Hygienists (ACGIH*), Industrial Ventilation, a Manual of Recommended Practices, 28 Edition
ASHRAE Standard 110-1995, Method of Testing Laboratory Fume Hoods
Existing Standards
2019 IAQA Annual Meeting
Q=VA ?
V – Face Velocity (Ft/min)
Q – Volumetric Flow (cfm)
A – Face Area (Ft2)
Check the Logic
2019 IAQA Annual Meeting
Understand The Problem
BAFFLE
SLOT
SLOT
Exterior Width = 2.51m (99”)
Interior Width = 2.33m (92”)
0.84m (33”)
1.50m (59”)
0.81m (32”)
2019 IAQA Annual Meeting
Make a Safe & Efficient Laboratory Fume Hood
Investigate a Direct Causal Relationship Between Containment
and Volumetric air Flow
Objectives
2019 IAQA Annual Meeting
DESIGN of EXPERIMENT
• Identify a Chemical Fume Hood
• Test the Hood (ASHRAE 110 – 1995)
• Modify the Hood Interior Shape
• Repeat the Test
• Analyze the Data / Compare the Results
Methodology
2019 IAQA Annual Meeting
How Much Data?
The Test (3 Minutes Ea.)
3 Air Flows (500, 800, 1200 cfm)
3 Diffuser Locations (R, L, C)
2 Static Vs. Dynamic
18 Tests Repeated 3 Times
54 Tests per Condition
10 – 12 Readings per Test
~600 Readings per Condition
Data Collection
2019 IAQA Annual Meeting
1
1.618…
The Golden Rectangle / Spiral
THE VORTEX SHAPE
Derived From the Fibonacci Series
1, 2, 3, 5, 8, 13, 21, 34, 55…………
The Golden Number Φ = 1.618…….
Geometry
2019 IAQA Annual Meeting
Demonstration Chamber
A Plexiglas enclosure; 24” wide, 24” high, 15”deep
A semicircular baffle in the topInterior with a single exhaust slot
An in-line fan draws 70 cfm
A perforated PVC pipe dischargesSmoke from a theatrical Fog Machine
Actual Model
2019 IAQA Annual Meeting
The Vortex Effect
Empirical observation confirms that
The air inside the enclosure flows in
the direction predicted by the
Golden Spiral of Fibonacci
2019 IAQA Annual Meeting
0
2000
4000
6000
8000
10000
12000
14000
16000
240 L/s - 500 cfm 380 L/s - 800 cfm 570 L/s - 1200 cfm
Co (ppb)-Traditional Co (ppb)-Vortex
Air FlowL/s (cfm)
Co-Traditional(ppb)
Co-Vortex(ppb)
240 (500) 14075 8973
380 (800) 4354 1484
570 (1200) 4370 309
Distribution by Air Flow
2019 IAQA Annual Meeting
8917
1460
316
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 200 400 600 800 1000 1200 1400
Co
-C
on
cen
trat
ion
Ou
tsid
e (
pp
b)
Air Flow (cfm)
Concentration - Co / Air Flow
A Logarithmic Curve
2019 IAQA Annual Meeting
0.000
0.500
1.000
1.500
2.000
2.500
3.000
240 L/S - 500 CFM 380 L/S - 800 CFM 570 L/S - 1200 CFM
HO
OD
IND
EX –
LOG
(C
0/C
I)AIR FLOW – L/S (CFM)
HI-Traditional HI-Vortex
Air FlowL/s (cfm)
HI-Traditional HI-Vortex
240 (500) 1.196 1.395
380 (800) 1.705 2.176
570 (1200) 1.704 2.858
Ci (ppb) 220856 222600
HI = -Log (Co/Ci) Eq. (1)Co = Concentration Outside the HoodCi = Concentration Inside the Hood
The Hood Index
2019 IAQA Annual Meeting
HI = Vc (Q) + b Eq. (2)
-Log (Co/Ci) = Vc (Q) + b Eq. (3)
Q= [-Log (Co/Ci) – b] / Vc Eq. (4)
HI = Hood IndexCo = Concentration Outside HoodCi = Concentration Inside HoodVc = Vortex Constant (slope)Q = Volumetric Air Flow (cfm)b = Y-intercept (Q = 0)
Doing the Math
2019 IAQA Annual Meeting
Q = 425 L/s (900 cfm) is an Intuitive Estimate
Divided by The Hood Internal Volume is 12 Air Changes / Minute
The Hood Index, HI = 2.28
The Dilution Ratio (Co/Ci) Becomes (1/190)
Expressed as a Percent 99.5% of the Tracer Gas Emitted is dissolved inside the Hood with the Sash Fully Open
Work the Problem Backwards
2019 IAQA Annual Meeting
Verification
Perform Operational Test
425 L/s (900 cfm)
Include Sash Positioning
The Result Is 36 ppb (0.036 ppm)
PASS!
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Researcher & Industrial Hygienist
Improved Safety
- Constant Volume / Variable Face Velocity
- Known Dilution Ratio (Co/Ci) = (1/190)
- Design of Experiments – TLV in (ppm)
2019 IAQA Annual Meeting
Engineers & ArchitectsHarness Turbulence
Vortex Ventilation
• Simplified Design using 12 Air Changes / Minute
• Rigid Structure with no Moving Parts, no Utility Connections
• Simplified Controls, High / Low Switch
2019 IAQA Annual Meeting
Laboratory Facility Owners
$ - Reduced Operating Cost (~1/2)
$ - Easily Retro-fit Existing Facilities
$ - One Year Pay-back on Capital Projects
$ - Uniform Hoods That Meet Standards
2019 IAQA Annual Meeting
Bibliography
• Fuller, F., Etchells, A. W.: The Rating of Laboratory
Hood Performance. ASHRAE J. 21(10):49-53
(1979)
• Meisenzahl, L.. R., Vortex Ventilation in the
Laboratory Environment. Journal of Occupational
and Environmental Hygiene (2014)
• Meisenzahl, L. R. Energy Solution for Laboratory
Facilities. ASHRAE Translation (LV-17-013) (2017)
2019 IAQA Annual Meeting
Key Learnings
• Fume Hood operation is a dilution process, not velocity capture
• Air flow inside a fume hood is turbulent, not laminar
• Fume hood containment (safety) is a function of volumetric air flow (cfm),
not face velocity (Ft./in.)
2019 IAQA Annual Meeting
Benchmarks
• A fume hood needs 12 air changes per minute (acm)
• The vortex hood has a dilution ratio (1/190)
• A fume hood only needs 2-position controls
2019 IAQA Annual Meeting
Practical Application
• Survey – Go to the Lab. Is the user safe?What information is posted on the hood.What is the hood Volume?What is the air flow when the hood is in use?
• Evaluate – Compare to benchmarks< 12 air-changes/min. – Unsafe!> 12 air-changes/min. – Wastes Energy
• Monitor – Constant Volume when in use.A static pressure gauge indicates air flow