Helpful Hints on Effective Use of Fume Hoods
A fume hood is a ventilated, enclosed work space intended to capture, contain and exhaust harmful or dangerous fumes, vapors and particulate matter generated by procedures conducted within the hood.
Fume Hood Locations
Proper location of the fume hood is a matter of great importance. The fume hood should be located in a place that is not exposed to excessive traffic, cross drafts and air turbulence from windows or doors. It must not block the means of egress in case of fire, explosion or the release of toxic materials from the hood.
Most Common Types of Fume Hoods
- Conventional fume hood - As the sash is lowered the air flow increases.
- Air by pass fume hood - Slots allow air to be pulled in at the top. This keeps the air flow from increasing rapidly as the sash is lowered, and decreases the turbulence.
Types of Sashes
- Vertical Sash - Up and down.
- Horizontal Sash - Side to side.
- Combination Sash - Both vertical and horizontal.
Operations and Procedures
- Make sure the fume hood is operating before starting work. Although it is not the most scientific, a simple way to tell if the fume hood is working is to tape a piece of tissue to the bottom of the sash. This will act as a wind sock to indicate the direction of air flow. When the hood is operating properly, the tissue should be pulled into the hood.
- If the fume hood has a monitor it will indicate air flow to the hood. If the alarm sounds or the monitor lights indicate low flow, work should be stopped, equipment turned off, the sash lowered, and lab personnel should leave the area if highly toxic or volatile chemicals are being used. If the fume hood is not functioning, call Building Maintenance at (7-2059). If it works, but you are not sure it is operating correctly or if you have questions regarding operation or safety, please call OSEH (3-6973).
- Fume hood alarms should never be disengaged or turned off.
- Fume hoods with manual controllers should be set to minimum and the sash closed when not in use. Make sure to turn the controller to maximum for the 100 fpm position before using the fume hood.
- Recognize the limitations of the fume hood. Only use fume hoods for those activities which can be performed safely.
- Always wear required personal protective equipment, (gloves, goggles, lab coats, aprons, etc.).
- Whenever possible, lower the sash to the lowest position when working in the fume hood to provide a safety shield for the face and upper body.
- All experimental materials and equipment should be placed towards the back of the fume hood, and at least 6 inches back from the face. This will allow maximum air flow draw and minimize the effects of cross drafts. Avoid blocking off rear baffle openings. For proper air circulation, large objects should be blocked up 2 to 3 inches above the work surface. When putting objects on blocks, leave spaces between blocks.
- Many things can affect air flow: room air supply vents, windows, doors, even a person passing by can create a 200 fpm air movement. Try to keep all windows and doors shut and pedestrian traffic to a minimum when working in the fume hood. Also, avoid rapid or excessive movement in front of the fume hood. These steps will help prevent turbulence caused by cross drafts.
- Avoid placing one's head in the fume hood.
- While performing any ongoing procedures or reactive experiments, the fume hood should not be left unattended for long periods of time.
- Fume hoods are not to be used as permanent storage for chemicals or equipment.
- Good housekeeping for fume hoods is important to keep surfaces and equipment from being damaged. Periodically clean the interior and exterior surfaces and the sash. Spills should be cleaned up immediately with surfaces wiped with water or an appropriate neutralizing agent.
- Keep papers, paper towel, work surface diapers, vials, or any other small objects from being pulled up the back, if no grill is present to prevent it.
- Close the sash fully when the fume hood is not in use.
- All personnel using the fume hoods should be fully trained in their proper operation. This includes knowledge of designed sash height to allow 100 fpm face velocity, controller operation, and monitoring devices.
Standards
- The face velocity, which is the air moving into the fume hood entrance or access opening, should be 100 fpm for standard fume hoods.
- No other types of exhaust can be connected to the fume hood exhaust system without proper engineering by Plant.
- Use of perchloric acid requires a special fume hood.
- Labels and arrows are placed on the face of the fume hood by OSEH. These indicate a measured velocity of 100 fpm at a specific sash height. Work in the fume hood should not be performed with the sash at any height higher than that marked by the label and arrow.
- Whenever maintenance work is performed (new motor, repairs, modifications, relocation, a new fume hood being installed, etc.) the air flow should be checked and the fume hood certified by OSEH.
- Periodically, routine maintenance will need to be performed, requiring one or more fume hoods to be shut down. Depending on the type of repair, your cooperation may be required in sealing and/or removing all chemicals from within the fume hood. This is to prevent exposure to workers on the roof who may be exposed to the effluents from the stacks.
- All fume hoods should have the air flow checked and be certified once a year by OSEH. If your fume hood has not been certified within the last year or if you have any questions regarding fume hoods please call OSEH (3-6973).