|
4: Chemical
Fume Hood Use
A well designed fume hood, when
properly installed and maintained, can provide a substantial degree
of protection for
the experimenter,
provided its proper use and limitations are understood.
The determination that a hood
is necessary for a particular process should be based on a hazard
analysis of the process under consideration. Such an analysis would
include a review of the physical characteristics, quantity, and toxicity
of the materials to be used, the volatility
of the materials present during the procedure, the probability of
their release, and the number and sophistication of manipulations,
etc. More subjective factors such as the skill and expertise of the
individual performing the work should also be considered.
The Office of Environmental Health & Safety
categorizes chemical fume hoods as described below, primarily on the
basis of face velocity .*
| Class A: |
Appropriate
for most operations requiring local exhaust ventilation to control
the exposure of
personnel to hazardous materials; however, if absolute containment
is required, the use of a glove box should be considered. (Average
face velocity between 95 and 125 feet per minute) |
| Class B: |
May not be appropriate for
some operations. The hood user should evaluate its suitability
for current and anticipated uses on a case-by-case basis. |
| Class C: |
Not suitable for the manipulation
of hazardous materials. |
Not all class B and C hoods must
be brought up to the class A standard. Many less hazardous operations
can be performed in a hood not meeting the class A criteria. Each fume
hood is rated during the semi-annual survey conducted by the Environmental
Health & Safety Office. The Class is indicated on the hood inspection
sticker and on the Fume Hood Survey Report sent to the individual designated
by the Department as responsible for the hood. Any changes or improvements
to a particular hood must be initiated by this individual. If you have
questions about the current status of a specific hood or its adequacy
for a particular application, contact Environmental Health & Safety.
Fume Hood Work Practices
The protection afforded by a
fume hood is only as good as the work practices of the hood user. The
following are general guidelines to be followed when working in the
hood:
- Know the toxic properties
of the chemicals with which you work. Be able to identify signs and
symptoms of overexposure.
- Mark a line with tape 6 inches
behind the sash and keep all chemicals and equipment behind that
line during procedure. This will help to keep vapors from escaping
the hood when air currents from people walking past the hood, etc.
interfere with air flow at the face of the hood.
- Keep the sash completely lowered
anytime "hands-on" experiments are not in progress or whenever
the hood is on and unattended.
- Never utilize the hood unless
there is some indication that the hood is operating. A tissue taped
to the sash or inside the hood provides a good indicator of air flow.
- Check the magnehelic gauge
reading and compare it with the reading documented on the hood inspection
sticker. If the reading differs significantly from that on the sticker,
the hood may not be operating sufficiently.
- The hood is not a substitute
for personal protective equipment. Wear gloves, safety glasses, etc.,
as appropriate.
- Visually inspect the baffles
(openings at the top and rear of the hood) to be sure the slots are
open and unobstructed.
- Do not block baffles. If large
equipment is in the hood, put it on blocks to raise it approximately
two inches so that air may pass beneath it.
- Do not use the hood as a storage
cabinet. Keep only the materials necessary for the procedure inside
the hood. If chemicals need to be stored in the hood for a period
of time, install shelves on the sides of the hood, away from the
baffles.
- Keep the sash clean and clear.
- Clean all chemical residues
from the hood chamber after each use.
- All electrical devices should
be connected outside the hood to avoid sparks which may ignite a
flammable or explosive chemical.
- DO NOT USE A HOOD FOR ANY
FUNCTION FOR WHICH IT WAS NOT INTENDED. Certain chemicals or reactions
require specially constructed hoods. Examples are perchloric acid
or high pressure reactions. Most special use hoods are labeled as
to the uses for which they are designed. If you have any questions
about the capabilities of a particular hood, contact Joan
Hutzly, EHS at 8-6251.
Return to Top
|
