Chemical Fume Hood Testing

Testing Procedure

  1. Position the sash so that the fume hood opening is 18 inches.
  2. Puff smoke around the opening of the hood by using the Ventilation Smoke Tubes. No smoke should come out of the hood.
  3. Divide the fume hood opening into nine squares.
  4. Turn the Alnor thermoanemometer to the Temperature position to check the battery. The reading must be 1, if 0, recharge the battery. Turn the Alnor now to the Velocity position.
  5. Measure the velocity of the air at the center of each of the nine squares. This is accomplished by placing the probe of the Alnor at the center of the square. Face the red dot on the probe directly outward and hold the probe directly in line with the sash. Allow the Alnor time to stop fluctuating between readings. When a fairly constant reading is shown on the Alnor, push the Hold button, then release. This will enter the reading into the Alnor's memory. Continue taking readings and holding them until all nine are done. After "holding" the ninth reading be sure to "release" it. To obtain the average of the nine readings, push the Hold button and hold it down until the word "hold" appears on the display. Push the Change button to see if nine readings were entered. If any number other than nine appears, you will have to start over.
  6. Put the sash at a six inch open position.
  7. Divide the fume hood opening into three squares.
  8. Follow step 5 above for the three measurements.


  1. Fill out the information asked for on the top of the Fume hood Face Velocity Profile form. Write in the Room no. and Hood no.
  2. Fill in the readings in the appropriate squares on the form and write in the average reading.
  3. If a fume hood does not pass, tape a Warning sign onto the sash, and cross out any earlier inspection stickers. Note: After a work order number has been assigned, go back to the Warning sign and write in the work order number.
  4. If a fume hood does pass, fill out an inspection sticker and affix it to the front of the hood. The metal frame of the hood is a good location for the sticker.
  5. If there is not a yellow "Sash Warning" sticker on the hood, affix one to the sash at either the left or right bottom corner.

Determining Whether to Pass a Hood

The following three conditions must all be met in order for the hood to pass:

  1. The average face velocity with the sash at an opening of 18 inches must be a minimum of 100 fpm.
  2. The average face velocity with the sash at an opening of six inches can not be greater than 300 fpm.
  3. Smoke can not come out of the hood.
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