Guidelines for care & Use of Dry Solvent Stills [Example]

3. VENTILATION AND PROPER USE OF HOODS
1. Ventilation System
Laboratory hoods serve as very convenient “designated areas” for working with dangerous
chemicals and you should take advantage of them whenever you feel it necessary.
The hoods in the Salem Hall are designed to keep the concentration of all airborne chemicals
below the Threshold Limit Values (TLVs) or Permissible Exposure Limits (PELs) as defined by
OSHA and explained in the subchapter of this manual titled “A Guide to OSHA Air Concentration
Acronyms”. Active laboratory areas are constantly provided with 100% fresh air from the ventilation
system, with the exception of laboratories in room #s 101, 103, 105, 107 and 109. The room #s 19 and 20
have been given an entirely separate air-control system with 8 air changes per hour, again of 100% fresh air.
The exhaust system for the building as a whole provides for complete separation of intake air from
exhaust air. The two enormous fans on the roof drive the exhaust air through the exit stacks approximately
fifty feet upward, away from intake air openings.
2. Supply air for all Laboratory Hoods
The hoods located in all research laboratories of Salem Hall are “Kewaunee Hoodaire Airflow”
fume hoods, of the Variable-volume non-bypass type. This means that the hoods are constructed to
maintain a constant velocity air flow at the opening of the hood (face velocity) as one opens or closes the
horizontal window-sashes. In a non-bypass hood, air is fed into the hood through the sash opening and
through the air-foil only. Since the hoods empty air from the room at differing rates, as one opens or closes
the sashes, air must be fed into the room at matching rates, or one cannot maintain even air flows.
One make-up air valve is located above the ceiling tile in each research and newly renovated
undergraduate lab. These “Phoenix Control” air valves track the exhaust valves above each hood and
automatically adjust the make-up supply air for the room as the exhaust valve air volume changes.
If you do not notice changes in the noise level of these valves when a majority of the sashes in the
lab are closed or opened, the valve is functioning abnormally. Another indication, of course, is whether the
air flow in the room is normal and unchanging as one opens and closes the sashes or whether the air
pressure in the room feels normal as one opens or closes the door to the room. If the valves are obviously
malfunctioning, call maintenance at Physical Facilities (phone # 4255). Call this number if any problem
with the ventilation arises in research labs, undergraduate labs, or storage rooms.
The Kewaunee hoods with vertical sashes, made from standard Kewaunee sash plate glass, are
located in the back bench areas of the newly renovated undergraduate labs in room #s 102, 106 and 111
(and soon to be in rooms 101 and 105). They are Kewaunee “Visionaire” brand by-pass hoods. They have
face velocities of 60 feet per minute. These hoods are used for dispensing reagents to undergraduate labs
and storage of hazardous waste.
The small bench top hoods in the newly renovated undergraduate labs are Kewaunee “Visionaire
View 2010” hoods, with polycarbonate safety shields, sidewall slots on the outer wall rims to reduce air
turbulence at the face opening, and clear tops and sides to allow maximum visibility which working, thus
encouraging the student to work inside the hood. The safety shield in front provides added protection.
These constant volume individual station hoods were designed by Wake Forest University Chemistry
Department faculty members and Kewaunee representatives. They have face velocities of about 30 to 40
feet per minute.
TLVs and PELs are safe air concentration levels based on 8 hour average workdays, 5 days a
week. Since undergraduate students work an average of 4 hours one afternoon per week, their exposures
are not likely in any case to exceed the PELs or TLVs of common laboratory chemicals. If one can smell a
chemical, one has in most cases just reached the boundary line of concern and one should seek to make
more efficient use of the nearest laboratory fume hood. Take the chemical you are working with and place
it closer to or further back into the hood. Proper planning for lab experiments beforehand, however, will
take into consideration the need for working in a hood. You should not rely on smell as a safeguard against
potential hazards. Some chemicals with low PELs can be hazardous at levels below the odor threshold.
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