Chemical Fume HoodsThe laboratory chemical fume hood is the most common local exhaust ventilation system used in laboratories. Local exhaust ventilation is the primary method used to control inhalation exposures to hazardous substances. The system consists of a hood, ductwork, and an exhaust ventilation fan.
All fume hoods should have a continuous monitoring device to allow convenient confirmation of adequate hood performance. If a hood is found to have an improperly operating continuous monitoring device or lacks a device, contact REM to request repairs or installation of a continuous monitoring device. Common types of continuous monitoring devices are oil gauge manometers, Magnehelic gauges, and digital control indicators.
Fume hoods are surveyed annually by the Industrial Hygiene section of REM. The survey consists of measuring airflow velocity at the face opening of the hood, checking the hood sash for ease of movement as well as cracks and breaks in the glass, checking the hood light, and maintaining and recording the reading on the visual continuous monitoring device on the hood. Below are the method used by REM to measure airflow velocity of the various types of hoods found on the West Lafayette campus.
Horizontal Sash Opening Hoods: Position the sashes to obtain maximum face opening of the hood (half-sash). Ideally the measurement will be taken from the center of the face of the hood.
Vertical Sash Opening Hoods: The hood face will be defined as the area from the hood work surface or airfoil to the bottom of the hood sash. Raise the sash to the halfway point, or the sash stop if unit is equipped with a stop.
Combination Sash Hoods: Measure both ways (with vertical sash at half-sash; with horizontal sash positioned to obtain maximum face opening of the hood). Ideally the horizontal sash measurement will be taken from the center of the face of the hood. Two labels will be placed on the hood indicating the different approved working height/opening size.
Walk-in Hoods: close the bottom sash to the floor and raise the top sash 100%. If obstructions are in the area of the face of the hood, preventing proper sash placement, the hood will be posted with a "STORAGE ONLY." sign. Repairs will not be requested. A REM note will be left for the user, notifying of the status of the hood and instructing the user how to change the hood status.
Current Standard for Face Velocity Range and Appropriate Use
- General Use = Face Velocity (FV) 80 to 125 fpm
- 80 fpm ≤ FV ≤ 125 fpm
- Storage Only = Face Velocity less than 80 fpm or greater than 125 fpm
- FV < 80fpm or FV > 125 fpm
If adjustments to airflow or the continuous monitoring device are necessary, REM will request these adjustments. If other maintenance and/or repairs to the fume hood are required (such as broken sash glass or a burned out hood light), REM will contact the appropriate party, i.e., Building Deputy or Principal Investigator, and give a written notice of the specific repairs needed.
Upon completion of the survey of the hood, REM will record the:
- Face velocity measurement,
- Approved use status
- Date of inspection
- Name of person inspecting
- Expiration date
This information will be on a label and placed at the indicated approved working height related to that face velocity measurement. Hood users should place the hood sash at the working height indicated by the black arrow on the label when operating the hood.
Before using the hood, users should compare the reading indicated on the visual continuous monitoring device with the recorded reading on the sticker on or near that device. Instructions are printed on this sticker in the event of a variation in the two readings.
If You have any questions or comments about your chemical fume hood contact REM.
REM keeps an inventory of all of the chemical fume hoods, biological safety cabinets, and laminar flow clean benches on campus. For that reason, changes in location of these types of hoods should be reported immediately.