Knowledge about Face Velocity of Steel Fume Cupboard

The speed of air flow through the operating surface of the fume cupboard into the fume hood is called face velocity.Due to the storage or operation of toxic and harmful substances in the fume hood, the fume hood should have specific face velocity requirements, in order to avoid possible harmful gas or material leakage.The most widely adopted mean face velocity requirement is 100 ft/min (i.e., 0.5m/s), and control deviation can be within ±20 ft/min (i.e., 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 wind speed for the hood is 80-100 ft/min (0.4-0.5 m/s).

If there may be high toxicity in the fume hood 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 hood operation, the operator will stand on the front of the fume hood and operate the instruments and equipment in the 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 wind speed on the fume hood, the greater the eddy current will be.Therefore, it is not the higher the face velocity will produce better protection effect.

Similarly, when the wind speed of the fume hood is low, the dynamic changes inside the laboratory, such as the movement of the operator, will have a significant negative impact on the airflow suppression effect of the fume hood.

Therefore, it is necessary to establish standard laboratory operating procedures and fume cupboard use specifications.It is not recommended to operate the fume hood at face velocity below 60 ft/min (0.3 m/s).In too low face velocity, the protection performance of the fume hood can not be guaranteed.