Laboratory Fume Hoods
Laboratory fume hoods are one of the most important used and abused hazard control devices on campus. We should all understand that the combined use of safety glasses, protective gloves, laboratory smocks, good safety practices, and laboratory fume hoods are very important elements in protecting us from a potentially hazardous exposure.
Laboratory fume hoods only protect users when they are used properly and are working correctly. A fume hood is designed to protect the user and room occupants from exposure to vapors, aerosols, toxic materials, odorous, and other harmful substances. A secondary purpose is to serve as a protective shield when working with potentially explosive or highly reactive materials. This is accomplished by lowering the hood sash. If you believe your hood is not working properly contact EHS at (573) 882-7018 for an evaluation.
Guidelines for Using a Hood Effectively
- Check to be sure the hood has been inspected within the last 12 months.
- Read the Safety Data Sheets for materials being used in a hood. Note the physical, chemical, and toxicological properties of materials being used before hand.
- Turn on the light for proper illumination.
- Keep the hood clear of clutter and unused materials. Do not use a hood for long term storage. Storage reduces air flow and compromises hood capture efficiency.
- All work should be done at least six inches from the front of the hood.
- When large equipment is used, place on blocks to allow for a two inch air flow gap under the equipment.
- Always lower the sash when not working in the hood.
- Never place your head in the hood while an experiment is on going.
- Avoid quick movements while working or passing in front of the hood. Rapid movements may cause turbulence or a backwash resulting in hazardous vapor escape.
- Campus Facilities Maintenance can adjust the baffle according to the nature of the work:
- For hot or lighter than air compounds, position the baffle to exhaust from the top of the hood.
- For normal operations, place the baffle in the center position.
- For work with heavier than air compounds place the baffle to exhaust the majority of the air from the bottom vent.
- Fume hoods are not to be used for disposal of unwanted material. The cap of the unwanted materials bottle must seal the container.
- Hoods designated for radioactive material use need to be approved by Radiation Safety before use.
- Use of perchloric acid must be in a properly operating Perchloric Acid Hood with water wash capabilities.
A fume hood is a piece of safety equipment that can be misused to the extent that they can be less effective than expected. Injury from misuse can arise from two causes.
- From the fume hood not providing adequate flow rates for the work required (i.e. sash being left open or from excess clutter that reduces the containment of noxious substances).
- From the hood itself (i.e. if the fan belts are slipping, the exhaust duct has blockage due to paper towels being sucked into the duct, the duct damper is restricted).
Always realize the most likely person to be injured is the hood user. Escaping noxious material into the laboratory can also effect all laboratory occupants.
In case of a power outage, the hood sash should be lowered within an inch to maintain a chimney effect to keep some air flowing into the hood.
Care should be taken with use of paper products, aluminum foil, and other lightweight materials within a hood. For example, a single paper towel or chemical wipe can potentially decrease the airflow into the hood if it restricts exhaust flow.
How is the Fume Hood Inspected?
The air flowing into the hood is measured with a calibrated velocimeter. The sash is placed in the normal operating height, about 18 inches from the closed position for most hoods. A number of air velocity measurements are made by traversing the hood face. These flows are in units of feet per minute (FPM). The readings are then averaged. A smoke tube may also be used to characterize air flow movement.
The draw from a hood in good working repair should be between 80 to 120 FPM. Hoods operating between 60 to 79 FPM need service to increase air flow. Hoods with air flow in excess of 120 FPM should be serviced to reduce air flow. Hoods that have an airflow of less than 60 FPM must not be used and must be taken out of service. Never use a hood that has been tagged "Out of Service."
After a hood has been checked for air flow one of two stickers (green or red) will be attached to the front side of the hood. These stickers show the last date of inspection.
- A green sticker indicates by the checked box that either:
- The Hood meets the EHS average face velocity requirements (80 - 120 FPM).
- Service is requested (60 - 79 FPM). Keep the sash as low as possible during operation.
- A red sticker indicates a hood velocity that doesn't meet EHS average face velocity (less than 60 FPM).
How often is the hood checked?
Campus hood surveys are conducted annually. The sticker should not be more than one year past the current date.
What is the sash position sticker?
This is a reminder that the hood shouldn't be used above the sash stop or about 18 inches above the closed position.
Who will service my hood?
Campus Facilities Maintenance will service only standard Laboratory hoods (not biosafety cabinets or perchloric acid hoods.) For maintenance of fume hoods, users should contact the Campus Facilities Work Order Desk at 882-8211. (In most cases, Campus Facilities is financially responsible for the maintenance of fume hoods.) The Principal Investigator or Laboratory Supervisor is responsible for maintenance of biosafety cabinets or perchloric acid hoods.
For more information of biosafety cabinets or laminar flow hoods go to the corresponding Biosafety page.
For more information on perchloric acid hoods contact the office of Industrial Hygiene at (573) 882-7018.