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

3. Preliminary Considerations for Safe Operation of Hoods
All hoods in Salem Hall have air slots in the back (bottom, mid, and top) to allow passage of air
from the “face” of the hood straight through to the back surface and out. The larger hoods have airfoils,
which prevent vertical displacement and guide the air horizontally. Air flow is much smoother if the slots
are not blocked by packing the hoods with everything imaginable. Do not overcrowd these hoods. Air
flows will be much smoother if equipment is raised 2 or 3 inches with support racks, lab jacks, or makeshift
raised platforms. The degree of air flow (referred to as “face velocity”) is not in itself an adequate measure
of hood efficiency. High flow rates of 100 - 150 feet per minute through hoods which are packed with
extraneous equipment, bottles, unnecessary chemicals, etc., only create high air turbulence and do not
operate as hoods, but rather as “expensive fans.”
The cabinets upon which these hoods rest contain venting holes leading to the hood. Therefore,
THESE CABINETS ARE IDEAL FOR STORAGE OF TOXIC OR OTHERWISE ODORIFEROUS
CHEMICALS. They also are lined with fireproof material. The hoods are in continual operation - they are
never turned off, unless there is a building ventilation shutdown, in which case you should evacuate your lab
if you are working with chemicals in the hoods or storing toxic chemicals below them in the storage
cabinets.
OSHA recommends 2.5 linear feet of hood space per worker if they spend most of their time
working with chemicals. Our research hoods have 3.5 linear feet per research student. The newly
renovated undergraduate laboratory hoods have 2 linear feet of hood space per student, each of whom will
spend at most 6 hours per week working with a hood. These undergraduate hoods are built much better
than most academic undergraduate hoods in other universities.
All electrical outlets, light switches, water and gas valves are located just outside of the research
hood chamber. The hood sashes SHOULD BE CLOSED when not in use, to save energy and cut down on
the expense of air maintenance. All hoods in Salem Hall will be inspected periodically and certified when
possible.
4. Hood Air Flow Monitors
All research laboratories, including one undergraduate teaching laboratory in room #7, the physical
chemistry lab, contain Phoenix Control Corporation Fume Hood Monitors. These monitors electronically
monitor the flow rate through your hoods and sound alarms when the flow rate falls below 70 feet per
minute. This indicates that you should evacuate the lab, unless there is merely a temporary malfunction of
the monitoring device itself. Read and follow the operating procedure for these monitors which follows this
section.
The monitor also regulates the air flow as sash doors are opened and closed during use. Horizontal
bar magnet sensors, located on top of the sashes and electrically connected to the Phoenix monitors,
increase the flow rate through the sash opening as the sash opening widens to a maximum flow rate of 100
linear feet per minute. As the door closes, the rate decreases to a minimum of 70 feet per minute. During
an emergency requiring a much higher air flow, such as a runaway reaction generating clouds of toxic
vapors, an emergency button can be depressed on the monitor to activate a sudden increase to 120 feet per
minute flow, simultaneously sounding an alarm. The mute button can then be depressed to silence the alarm
while maintaining the higher flow rate. Press the red emergency button again to return the flow to its
normal rate.
The large Kewaunee “Visionaire” hoods, located in back of the newly renovated undergraduate
hoods, also contain air flow monitors. The air-flow rate is 60 feet per minute. When the air flow falls
below this level, the Kewaunee “Air Alert 300” fume hood monitor will sound an alarm, indicating that
the flow rate will no longer maintain concentrations below the permissible exposure limits for hazardous
chemicals in the hood.
The green light on the monitor indicates normal air flow. When the air flow falls to a lower level,
a red alarm indicator light will flash and the alarm will sound. Please see the following diagram and
accompanying directions for use. IF ANY PROBLEM IS ENCOUNTERED WITH HOOD
MONITORING EQUIPMENT, WIRING, SASH SENSORS, OR HOOD AIR FLOW IN GENERAL,
STOP WORKING AND CONTACT THE LAB MANAGER AND CALL PHYSICAL FACILITIES
(PHONE #4255).
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