Knowledge about Face Velocity of Laboratory Fume Hood

The rate at which air moves through the front of a laboratory fume hood into the fume cupboard is known as face velocity. To prevent the escape of harmful gases or materials, fume hoods must meet specific face velocity requirements. The most common face velocity requirement is 100 ft/min (0.5m/s), with a permissible deviation of ±20 ft/min (0.1m/s).

United States Occupational Health and Safety Administration (OSHA) – 0.3 to 0.5 m/s

American Board of Industrial Hygiene (ACGIH) – 0.3 to 0.5 m/s

American National Organization for Standardization (ANSI) – 0.4 to 0.6 m/s

Prudent Practices — 0.3 to 0.5 m/s

American Fluid Power Society (NFPA) – “The fume hood shall strictly limit possible hazards to ensure personnel safety.”

German National Standard Institute (DIN) – 0.3m /s

China construction industry industry standard (JG/T) – 0.5m/s

In most cases, the recommended face velocity for the hood is 80-100 ft/min (0.4-0.5 m/s).

If there may be high toxicity in the lab fume cupboard or the external environment of the fume hood may have a serious impact on the performance of the fume hood, the face velocity requirement can be appropriately increased to 100-120 ft/min (i.e. 0.5-0.6 m/s).But the operating energy consumption of the fume hood is proportional to the size of the face velocity, and the higher the face velocity, the greater the energy consumption.However, at no time should the face velocity approach or exceed 150 ft/min (i.e. 0.75 m/s), as excessive face velocity can cause turbulence on the operating surface of the hood or inside the hood, resulting in leakage of air inside the hood.

In a typical fume cabinet operation, the operator will stand on the front of the fume cupboard and operate the instruments and equipment in the laboratory fume hood.At this time, the airflow from the front into the fume hood will generate eddy currents around the operator, and the eddy currents may bring out the polluted gas generated in the fume hood and pull up to the breathing area along the operator’s body around.The higher the face velocity on the fume hood, the greater the eddy current will be.

Having a higher face velocity does not necessarily provide better protection. Conversely, a low face velocity can disrupt airflow within the laboratory, especially when operators are moving around, compromising the fume hood's effectiveness. Standard operating procedures and laboratory fume hood guidelines should be established to maintain safety. Operating a fume hood below 60 ft/min (0.3 m/s) is not recommended, as it may compromise the hood's protective capabilities.