exposure risk of laboratory fume hoods · (aiha*), ansi/aiha z9.5-2012, laboratory ventilation...

2019 IAQA Annual Meeting

Lawrence Meisenzahl

Vortex Hoods, LLC

[email protected]

Phone: 302-660-6516

Exposure Risk of Laboratory Fume Hoods


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.


An Enigma

Safety Vs. Energy


Engineer

Research Chemist

Industrial Hygienists

Cast of Characters


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


1979 – 60 Ft./min. - W/ Sash Fully Open

Define the Problem


ERGONOMICS

Use of the Hood


Q=VA ?

V – Face Velocity (Ft/min)

Q – Volumetric Flow (cfm)

A – Face Area (Ft2)

Check the Logic


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”)


Make a Safe & Efficient Laboratory Fume Hood

Investigate a Direct Causal Relationship Between Containment

and Volumetric air Flow

Objectives


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


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


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


H

DD

O O SS

1

2 2

3 4

55

Fig. 3a Fig. 3b

Design / Architecture


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


The Vortex Effect

Empirical observation confirms that

The air inside the enclosure flows in

the direction predicted by the

Golden Spiral of Fibonacci


The ASHRAE 110 Tracer Gas Test

MeasuresSpill

Concentration


Results

VortexTrad

50000

40000

30000

20000

10000

0

Enclosure

Co

, P

PB


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


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


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


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


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


Verification

Perform Operational Test

425 L/s (900 cfm)

Include Sash Positioning

The Result Is 36 ppb (0.036 ppm)

PASS!


Researcher & Industrial Hygienist

Improved Safety

- Constant Volume / Variable Face Velocity

- Known Dilution Ratio (Co/Ci) = (1/190)

- Design of Experiments – TLV in (ppm)


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


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


Conclusion

Face VelocityFt./Min.

12Air

ChangesPer Minute

Paradigm Shift


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)


Questions?

Lawrence (Larry) Meisenzahl

[email protected]


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.)


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


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

exposure risk of laboratory fume hoods · (aiha*), ansi/aiha z9.5-2012, laboratory ventilation...

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