Fume hoods are a type of local exhaust that removes the contaminant at the source of generation. It is the most common type of ventilation engineering control used on campus.
The fume hood face velocity (in feet per minute or fpm) should be checked at least annually to verify proper flow rate. Check to see if there is a sticker on the side of the fume hood that indicates the maximum operating sash height with a date of the last inspection. EHSRM makes an effort to check all fume hoods annually but we need your help.
Some rules of thumb when using fume hoods
- Do not store chemicals in the fume hood
- Work at least 6” inside the hood
- Larger objects should be up on blocks or feet to allow air flow to travel underneath
- You can raise the sash higher than the indicated maximum operating height to place large objects in the hood, but always work with the sash at or lower than the maximum operating height
- When you are finished working in the hood, shut the sash and, if possible, turn the fume hood off.
- If the power goes out when you are using the fume hood, immediately shut the sash and evacuate the lab. Wait 15 minutes after power is restored before re-entering lab.
- Too much air flow is not necessarily a good thing. Eddies can occur which may push the contaminant back out of the fume hood. Call EHSRM if you suspect the fume hood is pulling too much air.
- If your fume hood is loud, it may indicate that mechanical attention is needed. Call EHSRM for a hood evaluation.
- Perchloric acid must be used in a dedicated fume hood with wash-down capabilities. Call EHSRM if you plan to use perchloric acid.
Other typical ventilation hoods on campus include laminar flow hoods, biosafety cabinets, snorkels (also called elephant trunks), and canopy hoods.
Laminar flow hoods use a HEPA or ULPA filter and vertical or horizontal air flow to blow air into the hood to protect the contents in the hood from contamination. These types of hoods do not necessarily protect the user of the hood.
Biosafety cabinets are designed to protect the user of the cabinet, the environment from the contents of the cabinet and in some cases the product or process in the cabinet through the use of HEPA filters.
NOTE: EHSRM does NOT certify laminar flow or biosafety cabinets.
Snorkel and canopy hoods
Snorkel and canopy hoods use the physical properties of the chemical or process to capture the exhaust (e.g. heat or lighter than air vapors). Snorkels are mobile and allow the user to place the hood directly over the work area.
NOTE: the snorkel face needs to be placed no further than one duct diameter away from the duct to be effective.