LABORATORY CHEMICAL HOODS AND OTHER ENGINEERING CONTROLS

Laboratory chemical hood Face Velocities

All Laboratory chemical hoods at University of Kentucky facilities should have face velocities between 80-120 feet per minute (fpm) with the sash at a "working height" (approximately 12 inches).  As a rule, Laboratory chemical hoods should not be operated with the sash fully open and should have the sash closed when not being used.  The office of Occupational Health and Safety (OHS) will conduct an annual Laboratory chemical hood inspection and certification program for all Laboratory chemical hoods at the university.  Laboratory chemical hoods with face velocities within the 80-150 fpm range may be used without restriction and will be marked with a Laboratory chemical hood sticker showing face velocity at a height designated with an arrow.  The face velocity range from 120 to 150 fpm does not significantly increase the safety of the user but does pose a large energy cost.  That is why UK tries to keep face velocities below 120 fpm.

Hoods Needing Repairs

Laboratory chemical hoods with face velocities below 60 fpm or above 150 linear fpm must be marked with a sign indicating that the hood may not be used for chemical manipulations.  A work order to repair these hoods should be processed as soon as possible.  For UKMC this can be done online or by contacting the MCPPD at 323-6281.  For Lexington Campus, contact your building administrator and/or operator.  Once the hood has been repaired, OHS will need to be contacted to reevaluate the hood’s performance.

Safe Work Practices for Laboratory Chemical Hoods

A Laboratory chemical hood cannot provide complete safety against all events that may occur in the hood, especially for toxic airborne contaminants with an exposure limit in the low part per billion range.  For ordinary exposures, however, a properly designed hood in a properly ventilated room can provide adequate protection.  Nevertheless, certain work practices are necessary for the hood to perform efficiently.  The following work practices are required; more stringent practices may be necessary in some circumstances.  From The American Conference of Governmental Industrial Hygienists in their text:  "Industrial Ventilation: A Manual of Recommended Practices:"

• All operations that may generate air contaminants at levels above the exposure limit must be conducted inside a hood.
• Keep all apparatus at least 6 inches back from the face of the hood.  A stripe on the bench surface is a good reminder.
• Do not put your head in the hood when contaminants are being generated.
• Do not use the hood as a waste disposal mechanism except for very small quantities of volatile materials.
• Excessive storage of chemicals or any apparatus in the hood will impair the performance of the laboratory chemical hood.  Store flammable chemicals in an approved flammable storage safety cabinet.  Store corrosive chemicals in a corrosive storage cabinet. 
• Be sure that the switch is in the "on" position whenever the hood is in use and test hood often for airflow (for example using a Kim wipe).
• Using hazardous solids (powders) in the hood may not be appropriate.
• Keep the slots in the hood baffles free of obstruction by apparatus or containers.
• Minimize foot traffic past the face of the hood.
• Keep laboratory doors and windows closed (exception: some laboratories are designed for the lab doors to be open).
• Do not remove hood sash or panels except when necessary for apparatus set-up. Replace sash or panels before operating.
• Do not place electrical receptacles or other spark sources inside the hood when flammable liquids or gases are present.  No permanent electrical receptacles are permitted in the hood.
• Use an appropriate barricade if there is a chance of explosion or eruption.
• If hood sash is supposed to be partially closed for operation, the hood should be so labeled, and the appropriate closure point clearly indicated.
• Where perchloric acid is heated above ambient temperature, vapors may condense within the exhaust system to form explosive perchlorates.  In such instances, specially designed Laboratory chemical hood exhaust systems must be utilized. These systems will have dedicated exhausts and a water washdown system and may be used for perchloric acid digestions only.
• All Laboratory chemical hoods should have spill protection lips (at the front of hood and for cup sinks located in the hood).

For more information about types of fumes hoods and their function, please take the Chemical Fume Hood training class online: https://ehs.uky.edu/classes/classes_ohs_0001.php#chemical_fume_hood.

Any questions or requests for assistance in evaluation of Laboratory chemical hoods may be directed to OHS (257-2924).

Most fume hoods on campus now are equipped with flow monitors.  These monitors are designed to give the user a guide for the proper function of the face velocity of the fume hood.