Thompson Rivers University
Thompson Rivers University

Fumehoods

Fumehoods

A Fumehood is an enclosed work area that:

  • is designed to prevent the spread of fumes/vapours to operators and other personnel in the area
  • is ventilated by an induced flow of air through a sash opening or working aperture, the height of which may be adjusted, which dilutes the fume/vapour
  • by means of an exhaust system, provides for the safe and remote discharge of the fume/vapour outside the building

Definitions

Baffle Removable plates incorporated into the rear or top of the work chamber to form a plenum between the work chamber and the exhaust duct connection to promote uniform scavenging of fume and the point of discharge.
Exhaust System All exhaust air ductwork, fan and associated equipment installed between the point of connection to the fumehood and the point of discharge.
Face Velocity The velocity of the air passing through the work opening measured in the plane of the sash. Measured in feet per minute or litres per second
HVAC System Heating, ventilation and Air Conditioning system (H-vac) relates to air handling systems designed for air quality, temperature, humidity and odour control. It also provides make-up air.
Make-up Air Air needed to replace the air exhausted from a room by the fumehood and other ventilation devices.
Plenum A low-velocity chamber used to distribute static pressure (from the fan in the system) throughout its interior.
Sash A transparent safety screen in the work opening of the fumehood, which can be positioned between the operator and the work chamber for protection. The opening can be adjusted vertically to vary the size of the opening and control the face velocity of air into the hood.
Sash Opening The dimension of the opening in the direction of the sash movement.

Operating Procedures

  1. Conduct all experiments that generate air-borne contaminants inside a fumehood. Always wear chemical splash goggles and a lab coat when working in a lab.
  2. The hood should be inspected annually by OH&S. Check the arrow sticker. If the date is not within the last year do not use the fumehood. Next to the date will be the average air velocity for the fumehood measured in feet per minute (fpm). The velocity should be greater than 100fpm for use with non-carcinogen chemicals. If carcinogens are being used the face velocity must be greater than 150fpm. Do NOT use carcinogens in a fumehood that has a red notice on it saying that it does not meet WCB's minimum airflow requirements for use with carcinogens. Departments have indicated which fumehoods they need to meet the requirements to use carcinogens - these hoods do not have any notices on them.
  3. The hoods were tested at specific sash openings. To achieve the same face velocity seen during testing the stickers with arrows should be lined up. During renovations to the HVAC system in the Science building in 1999 these were standardized to provide a 12-inch sash opening. Raising the sash higher than the labelled height will reduce the hood's efficiency. If the opening is not suitable to your needs phone 5139 to have it retested at a different sash opening.
  4. Prior to the start of any lab that requires the use of a fumehood a check should be made to ensure that the hood is drawing air. Taping a Kimwipe to the inside of the sash can do this by checking to see that it is moving. If it is not or there does not seem to be sufficient flow phone 5139 to have the hood checked. OH&S do not charge to test hoods. Be aware of changes in airflow as you are working.
  5. The face velocity normally ranges between 100 and 200 fpm, air (and associated chemical fumes) can be pulled from the hood and into the breathing zone by a number of factors including: Foot traffic, rapid arm/body movements, open doors and ventilation systems. Foot traffic in front of the hood should be avoided. Doors should be kept closed when the hood is operating.
  6. Chemicals and equipment should be at least 6-inches inside the hood. If work is done at the face of the hood contaminants may be 300 times greater than if done at the 6-inch mark. Tape at the 6-inch mark will help to keep the experiment inside the hood.
  7. Do not put your face inside the plane of the sash when air-borne contaminants are being produced.
  8. If a hood is working when people are not present because the experiment is still going on, information should be posted on the sash showing the name of the person conducting the experiment, what the experiment is and what are the potential hazards of the experiment.
  9. Do not use the fumehood as an extra storage cabinet. Chemicals and apparatus obstruct the airflow of an experiment using the fumehood. If there is an incident in the fumehood clean-up will be more difficult. Keep all chemical containers sealed to prevent the build-up of fumes. One hood in S237 has been designated for waste storage and cannot be used for experiments.
  10. Large pieces of apparatus should be elevated to allow airflow, with minimal turbulence, to flow under the apparatus to the baffle.
  11. No sources of ignition or spark must be present when flammable liquids or gases are being used. Permanent electrical plugs are not allowed in fumehoods.
  12. Keep the fumehood clean - remove old apparatus and chemicals. Clean any spilled chemicals. Make sure the glass of the sash is clean so you can see what you are doing.
  13. When not in use the sash should be closed down and the fan knocked off.