LABORATORY FUME HOOD SAFETY GUIDE
Laboratory fume hoods are designed to protect you by
providing an enclosed work area that has an air barrier between you and the
hazardous materials you work with in the hood. The fume hood directs airflow to
carry harmful contaminants away from you toward the rear of the hood and out
through the exhaust duct. By venting the harmful contaminants from the
laboratory, the fume hood maintains a safe and healthy environment for you and
those working near you.
Fume hoods should always be used when working with a
substance that has a threshold limit value *(TLV)
of less than 50 ppm. The TLV for a substance will be listed on the Material
Safety Data Sheet (MSDS).
Do not use fume hoods to evaporate hazardous wastes.
This practice is illegal. It violates the Clean Air Act and is punishable by
large fines and imprisonment.
Keep the fume hood sash closed at all times when the
hood is not being used.
Minimize the quantities of materials that might be
involved in a fire or explosion by limiting the amount of chemicals used in the
hood.
Fume hood airflow velocities are relatively low
(approximately 100 feet per minute) and airflow can be easily disrupted. Avoid
making rapid movements while working in a fume hood and avoid walking close to
a fume hood that is being used by a coworker.
Working with the sash at the proper level provides
protection against inhalation of hazardous vapors, chemical splashes and
splatters, fire, or explosion. The sash should be opened only as far as necessary
to access your work. All SPC fume hoods are tested annually and labeled to
indicate the proper sash stop point. This is the maximum opening for safe
operation of the fume hood. Do not exceed the sash stop point because airflow
will be insufficient to provide protection against contaminants in the hood.
Do not lean into the hood to work with hazardous
chemicals. This negates the protection the hood provides against inhalation of
hazardous vapors.
Chemicals should be placed
no closer than 6 inches from the front opening of the fume hood. Placing them
closer to the front opening interferes with the airflow and reduces the level
of contaminant protection for individuals working at the fume hood.
Place heating units at least 12 inches behind the sash opening.
In most cases, a baffle position of equal openings
at top and bottom gives the best performance because it provides good airflow
in both the lower and upper parts of the hood. However, when substances are
heated in the hood, the heat will cause the contaminants to rise within the
hood. In this case the baffle(s) should be adjusted so the top vent is fully
open and the bottom vent is partially closed. This will permit more air to be
exhausted from the upper part of the work area. When large volumes of dense
vapors are given off in the hood, they tend to sink within the hood. In this
case, the baffle(s) should be adjusted so the top vent is partially closed and
the bottom vent is fully open to allow increased airflow across the lower part
of the work area. Before setting up apparatus in the hood, verify that the
baffle(s) are set in the correct position for the procedure to be performed.
Place equipment so that it does not block airflow to
slots or vents in the baffle plate at the back of the hood. When possible,
elevate bulky equipment to allow air to flow under the equipment, as well as
around and over it.
Do not store chemicals inside a fume hood. Store them in designated chemical storage rooms or in flammable liquid or acid cabinets. If it is necessary to leave a small amount of chemicals in a fume hood, the fume hood should be kept running.
DANGER - If chemicals are stored inside fume hoods when
the exhaust fan is turned off, fumes will accumulate inside the hood and
ductwork creating the potential for dangerous accumulations of flammable and/or
corrosive vapors. This creates fire and health hazards in the vicinity of the
fume hood and these vapors will eventually be vented into the lab which will
extend the fire and health hazards even farther.
Do not use multiple electrical outlets inside the
hood. Run all equipment underneath the hood airfoil, along the front edge of
the fume hood, to external electrical outlets. In an emergency the sash can be
closed completely and cords can be unplugged without reaching into the hood or
creating the potential for sparks inside the hood. Cords should be secured with
ties to route them in such a manner that prevents trip hazards and accidentally
pulling them from their connections.
Gas, vacuum and water hoses that are required to
operate equipment used inside the hood should be routed under the airfoil,
along the front edge of the fume hood, so the sash may be closed completely. It
will also permit disconnection of equipment in the event difficulties occur
with an experiment. Hoses should be secured with ties to route them in such a
manner that prevents trip hazards and accidentally pulling them from their
connections.
Fume hoods that are not used regularly, should be operated periodically to ensure the sash moves freely and the exhaust fan and lights operate properly.
*TLV Threshold limit value is a
term used by the American Conference of Governmental Industrial Hygienists
(ACGIH) to express the airborne concentration to which nearly all persons can
be exposed day after day, without adverse effects. ACGIH expresses TLVs in the
following three ways:
TLV-C Ceiling
limit – the concentration that should not be exceeded even instantaneously.
TLV-STEL Short Term
Exposure Limit or maximum concentration for a continuous 15 minute
exposure
period.
TLV-TWA The allowable Time
Weighted Average concentration for a normal 8 hour workday or 40
hour
workweek.
Laboratory Chemical Hygiene an AIHA Protocol Guide, American Industrial Hygiene Association, Fairfax, VA 1995.
Occupational Exposure to Hazardous Chemicals in Laboratories, U. S. Occupational Safety and Health Standards for General Industry, 29 CFR 1910.1450, U. S. Government Printing Office, Washington, DC.
Prudent Practices in the Laboratory Handling and Disposal of Chemicals, National Research Council, National Academy Press, Washington, DC 1995.
SPC Safety/Environmental Services 3/00
Rev. 3/02