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Gary Carlin, MS, MBA, CIH, CHMM

Associate Manager, Safety, Health and Emergency Response

Battelle Memorial Institute, Columbus, OH

Phone: 614-424-4929

Email: carling@battelle.org

EEI Spring Occupational Safety & Health Committee Conference

May 3, 2011

Laboratory Fume Hood

Safety

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Hoods

• Outline

– Why important

– Basic Hood Function

– Smoke Test Demonstrations

– Basic Fume Hood Use Safety Guidelines

– Summary

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Importance of Learning About

Hoods• We rely on hoods to capture harmful chemical

emissions

- Volatile, toxic, and/or odiferous

- OEL < 50 ppm or 100 mg/m3

- LC50 < 200 ppm or 2000 mg/m3

- Animal studies

• PRIMARY engineering control in a laboratory setting. Trusted the hood to protect staff.

• They are very protective if they are used correctly

• If used improperly, can have potential exposures.

• The key to proper use is understanding how they operate

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Hood Design

• Normal Hood (side view)

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Hood Design

• Variations of Hood Design

– Standard (no bypass)

– Bypass

– Variable Air Volume

• Variations of Hood Control

– Switch to lower flow when sash is closed

– Switch to lower flow when no one is in front of hood

- Usually for energy conservation. Not the best choice if working with high hazard materials.

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“Standard” Fume Hood

• In constant volume systems, the face velocity will increase with reduced sash height.

• Face velocity could be three or more times than the measured velocity.

• The hood performance does not usually deteriorate because the hood opening is reduced and the lowered sash acts as a partial barrier. It is important to check to verify this point (usually visual smoke). (ANSI/AIHA Z9.5)

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Bypass Fume Hoods

• As you close the sash, the bypass is opened. You have the same volume of air passing through the hood, it is just re-directed. There may be some increase in face velocity as you close the hood sash.

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Variable Air Volume Fume Hood

• With a variable air volume hood, a damper or variable speed motor reduces total air volume through the hood as the sash is closed. This maintains average face velocity essentially the same throughout the sash operating height.

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Hood Function

• Normal Hood function (Top View)

• ANSI/AIHA Z9.5 Recommends chemicals/operations not be closer than 6” from the sash face.

• Important to keep nose/face out of the hood!

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Hood Function

• Normal Hood function (side view)

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Hood Function

• Normal Hood function (Sash Closed)

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Hood Function

• Hood function (Sash Raised Quickly)

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Challenged Hood Air Flow

• Normal Hood function (Blocked)

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Challenged Hood Air Flow

• Hood function (Two Too Close)

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Hood Function

• General Information

– Users should not make any adjustments to the baffles

- This may affect the air balance of the hood

- Baffles help accommodate heating items in the hood which makes vapors rise

- Adjustments should only be undertaken by a qualified individual followed by flow and smoke testing the hood

– Whenever you have placed a substantial amount of items in the hood, it is a good practice to measure the flow and conduct a visual smoke test to ensure proper operation

– Do not remove hood appliances to accommodate work (I.e., air foil)

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Smoke test Demonstrations

• Smoke is used to visualize hood capture and containment.

• First video demonstrates good capture with little obstruction to flow:

– Note that most of the smoke flows to the rear

– Small amount circulates up by the hood sash

– lip on tray causes build up of smoke in container

– Video

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Smoke Test Demonstrations

• Next Video demonstrates the effects on capture in spite of large objects in hood that have been properly placed

– Due to large objects in hood, more smoke ends up circulating high in the hood

- Caused by direct pathway to bottom baffle being obstructed

– Note how the smoke circulates near the sash

– Back side of sash has chemical vapor right up against it. Opening a closed sash quickly can result in these vapors entering the room.

– Movement in the hood, and further blockage of the flow can cause momentary excursions of such a large build up of vapors (smoke)

– Video

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Smoke Test Demonstrations

• Loss of Containment

– First with good set-up, then with large item in front of hood and projecting into hood

– Loss occurred due to a combination of things

- Item in front of hood blocks about a foot of the left side of the hood

- Structures outside the hood project into hood

- Individual blocks the rest of the left side of hood

– Video

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Room Placement of Laboratory

Hoods

Guidelines for placement of laboratory fume hoods include:

• Locate so that exit from the laboratory will not be impeded in the event of a fire or explosion within the hood structure itself

• Locate away from high pedestrian traffic lanes in the laboratory to avoid disruptions to the airflow entering the hood.

• Cross currents from room ventilation should be avoided.

• Hoods should not be installed in a location where it is likely to be affected by another piece of equipment, (e.g., another fume hood)

• A fume hood should not be installed without first considering whether the laboratory’s supply air system will be able to replace all of the air exhausted.

• The National Fire Prevention Association (NFPA) Code 45 calls for replacing the laboratory with slightly less than the amount of air exhausted from the hood. This causes a slight inflow of air into the laboratory.

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Hood Flow Monitoring/ Design

• New Installation

– ASHRAE 110-95 gives a relative, quantitative determination of hood capture.

1. Average opening Flow check @ each 1’ square section of opening

2. Smoke testing to visually verify capture.

3. Tracer gas released in hood. Mannequin put at hood face to check breathing zone.

Take measurements at the approximate center of one-

foot squares across the face of the hood.

Sash

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Hood Flow Monitoring/ Design

• Ongoing Use

– Should have audible/visual alarms on hood to indicate low and high flow situations (sometimes you CAN have too much of a good thing.)

– ANSI/AIHA Z9.5 “Laboratory Ventilation” gives additional guidelines for routine testing, design and use of laboratory fume hoods.

– ACGIH Industrial Ventilation Manual also provides guidance on design and work practices in hoods.

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Basic Fume Hood Use Safety Guidelines

• SET UP

– Ensure a recent face velocity check has been completed for your hood.

– Good practice to check it with vaneometer (daily before use)

- Check a few spots

- 60 feet/minute has been used as a reference in the past; however, must have ideal conditions and at this flow rate, very susceptible to movement in and around hood.

- 100 feet/Minute +/- 20% (80 to 120 feet/minute) is the standard used at Battelle. Additional guidance provided in ANSI/AIHA Z9.5

- Don’t get too close to side/top/bottom

- Check it with the hood setup as you will use it

- Stand away from the hood face as you take a measurement

– Set things up ergonomically

- Can you easily reach all of the necessary items

- Without reaching across items that can be tipped over

- Without having to put your head in the hood

- Are things setup for a natural flow of events?

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Basic Fume Hood Use Safety Guidelines

– Do not block the air-flow

- Two individuals in same hood should leave some space between

- Do not bunch together items in a hood

- Turn items to smallest side to keep from blocking air flow

- Keep items away from the side of the hood

- Raise larger objects up off the floor of the hood

- Work with the sash down such that it is between your work and your face (look through the glass)

- Try keep hood sash height so it is less than 18” whenever possible. (Sash stops may be appropriate)

- Communicate with the individuals conducting your face velocity checks indicating the maximum height you use.

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Basic Fume Hood Use Safety Guidelines

• General Requirements (Cont)

– Move the sash slowly (especially when raising)

– Do not walk around near the hood

– Back away from the hood slowly

– Move your arms slowly

– Pay attention to items in the hood that move air

- Pumps

- Motors

- Heat Sources

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Spill Containment & Control

• Trays, sorbent mats, etc. to contain possible spills

• Use minimum amount, smallest containers, metering pumps

• Use safety jackets around glass bottles

• Keep appropriate spill kits easily accessible (along with PPE)

• Ensure hazard assessment is appropriate to the materials being used. Extremely hazardous materials may require additional engineering or administrative controls. A fume hood may not be the best choice…

Don’t use your fume hood as a

chemical storage facility.

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Summary• To be safe, you must understand

the use and limitation of fume hoods.

• It is all about air flow, do not block it or divert it, if there is any question, have it evaluated

• Make sure the hood works before beginning operations

• Keep items behind at least 6” behind the sash plane

• Evaluate your operations and make sure a fume hood is the best protective measure for your application.

• There several excellent references available to help install and maintain laboratory hoods

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References

• ASHRAE 110-95

• AIHA/ANSI Z9.5

• ACGIH Industrial Ventilation: A Manual of Recommended Practice

• How to Select The Right Laboratory Hood System. LabConco(http://labconco.dayitech.com/brochure/hood/select_fume_hood.pdf)

• National Fire Protection Association 45

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Questions?