Rob McClain, Chair 608-262-5615 mcclain@chem.wisc.edu
Berry, J.
Hill, N.
Ivancic, M.
Whitlock, H. W.
Wilkinson, C.
Safety Equipment and Practices in Chemistry Department Laboratories
Fume hoods - general principles
First and foremost, fume hoods are a safety device. In order to achieve the greatest margin of protection for yourself, you must adhere to the proper operating procedures.
From the perspective of personal self-interest, you should strive to:
maintain the sash at the lowest possible position when you are working at your hood
keep the sash closed when you are not actively working at your hood
make sure that the horizontal sliding panels are in place. Do not remove any of the sliding panels from the fume hoods! They are there to protect you and your lab-mates. The vertical sash should be lowered at all times, except when setting up a large apparatus.
Adjustments
face velocity sensor -- in case of malfunction, contact Tom Foseid.
baffle adjustment -- follow instructions on the hood to make adjustments depending upon the density of the evolved gases and location in the hood
Specialty gas connections -- each hood can be connected to two different gas tanks to allow easy access to these gases inside the hood
In the vacuum pump cabinet, the tygon tubing with the plastic clamp is the drain line for the trough at the front edge of the fume hood. (Note the tiny drain hole on the left-hand side of the trough.)
Cabinets under the fume hoods are vented into the hood. These cabinets are intended for chemical storage (acids, bases, corrosives) but not for flammable solvents.
See further down the page for lots more useful information about fume hoods.
Snorkel drops. At several places in each lab an air intake is provided which can be connected to snorkel tubing to directly vent fumes and vapors (e.g, vacuum pumps). These air intakes are active whether or not tubing is connected to them; the air flow does not need be adjusted if you make a connection.
Waste solvent containers. A cabinet under one of the fume hoods in each lab is designed for waste storage containers. This cabinet contains two small pallets on wheels.
Red light switches (Shain wing only). The red light switches are to be left on at all times unless some particular procedure requires that the lab be more completely darkened. In case of a power outage, an emergency generator will provide power to these lights whether the switches are on or off.
Emergency power circuits (Shain wing only). The red electrical outlets will be powered by the emergency generator in case of a power outage.
Please locate these items in your new lab: fire extinguisher, safety shower, emergency eye wash. Try out the shower and the eye wash so you know how they work; you might want to place a bucket in the appropriate place first!
Ideally all solvent stills would be set up in a hood.
An emergency call station, which automatically connects you to the Campus Police, is located next to the elevators in the Shain wing.
Know the location of fire alarm switches. The fire alarm system may be activated by pulling the switch, and may also be activated by various heat or smoke sensors throughout the building. The sprinkler system (Shain wing only) is activated only by heat. And only those sprinklers near the heat source are activated. If you activate the fire alarm:
Fight or contain the fire if you can do so safely. Otherwise do as instructed in (b).
Send someone, or go yourself, to the Central Control Station, room 1239. Report the nature and extent of the fire to chemistry and/or Madison Fire Dept. personnel who will respond to this location.
Eye protection -- Wisconsin law requires eye protection for all laboratory workers. No one should enter a lab with out proper eye protection. Safety glasses are the minimum requirement for eye protection. Wear enclosed goggles or a face shield when working with anything under pressure or where there is danger of splashed liquids or shattering glass. If you work with ultraviolet or laser light, wear protective lenses specific for the wavelength.
Secondary containment for chemical transport -- Use secondary containment. No matter how careful you are, containers can drop and bottles can break. Use a tray or a bucket to hold your chemicals in transit and contain these possible accidents. Good secondary containment can mean the difference between a small inconvenience and a major building evacuation. Safety buckets are available in the 5th floor stockroom.
Keep incompatible chemicals separate -- Keep incompatible chemicals separate. Use your knowledge of chemical reactions to separate chemical stocks into compatible categories. Appendix F of the UW Chemical Safety and Disposal Guide provides guidelines for compatible storage of chemicals.
Minimize use of Particularly Hazardous Substances. The UW-Safety department has established a list of chemicals that are considered (by various US Government agencies) to present an unusual threat to laboratory workers. A number of these are very common chemicals in synthetic laboratories. If you need a substance on this list, please complete the approval form and have it signed by your supervisor. Note: if certain compounds from the list (e.g. methylene chloride, chloroform) are in routine use in the lab it is not necessary for each researcher to complete an approval form. However, new researchers joining the group should be informed about the use and toxicity of these chemicals during orientation to the lab.
Safety considerations when moving a lab.
Elevators -- Large amounts of chemicals do not belong on the same elevator as the general public. Use the freight elevator (Daniels wing) or move large volumes of chemicals outside of normal business hours if you must use the elevators in the Shain wing.
Compatibility -- When moving, think about what would happen if two containers near each other both broke. Examples: Don't move acids and bases together. Don't move strong oxidizers with combustibles.
Secondary containment -- Any chemical container which could leak or spill must be placed inside an unbreakable container. See #11 above.
Containing spills If you will be moving large volumes of liquid chemicals, talk to the building manager about obtaining a supply of absorbent to use in case of a spill.
Safety related questions should be addressed to the building manager or the chair of the Safety Committee. The UW-Madison chemical safety website is http://www2.fpm.wisc.edu/chemsafety/
More information on Fume Hoods
Airflow Characteristics
The sash, in combination with the bypass grille located above the sash, determines the airflow characteristics of the fume hood. Although the sash position does not control the volume of air that passes through the fume hood, the sash position does control the velocity of air that passes through the fume hood. The relationship between sash position and velocity of air through the face of the fume hood depends on the specific design of the hood and bypass grille.
The University's Safety Department inspects our fume hoods once each year. Yellow sash height markers are adjusted on the basis of actual measurements of fume hood face velocity. In order to maintain a face velocity of 80-100 linear feet per minute, your sash must be located at or below the yellow sash height marker. For most of our hoods, the face velocity remains relatively constant at any position below the sash marker. When you raise your sash above the marker, you compromise your own safety, because the face velocity will drop below the recommended threshold. From the perspective of personal self-interest, you should strive to maintain the sash at the lowest possible position when you are working at your hood.
A potentially confusing issue arises because many of our fume hoods have two sash height markers. The black marker stating "100 FPM face velocity with sash at this line" dates back to the major fume hood upgrade project of 1985. The yellow marker stating "Sash Level" reflects a measurement of 100 FPM face velocity under actual operating conditions by the University's Safety Department.
A common misconception: The greater the face velocity of your fume hood, the greater your margin of safety.
Not Necessarily: Optimum face velocity is 80-120 linear feet per minute. At lower velocity, the fume hood may not capture and remove vapors at a sufficient rate. At higher velocity, air flow may become turbulent, producing eddies and backflows that retard the rate of removal or cause leakage of vapors outside the hood (through the sash or the bypass grille).
The Sash Functions as a Blast Shield
The sash is a blast shield, and the sash provides primary containment in the event of fire. Your sash should be closed when you are not actively working at your hood. Moreover, you should be vigilant that your fellow lab occupants maintain closed sashes when they are not working at their hoods.
Just a few years ago, a violent explosion occurred in a fume hood in which the sash was not closed. Glass shards, debris, and chemicals were scattered throughout the laboratory. All occupants of the laboratory - not just the coworker performing the reaction - would have been at risk. Miraculously, the lab was not occupied at the time (ca. 7:00 pm). In cases where you are performing experiments that are suspected to present an explosion hazard, you should utilize a portable blast shield inside the hood in addition to a closed sash. You should also inform your fellow lab occupants when you are performing potentially hazardous procedures. Again, from the perspective of personal self interest, you should strive to maintain the sash at the lowest possible position at all times.
Horizontal Sliding Panels
Most of our fume hoods are fitted with one or more horizontal sliding panels. These sliding panels should be in place at all times. Removal of the sliding panels compromises your safety in two ways: first, it increases the open area of the fume hood, thereby decreasing the velocity of air through the face of the hood; second, it eliminates the protection afforded by the blast shield.
Energy Conservation
Laboratory buildings containing fume hoods consume large amounts of energy. In a typical synthetic chemistry laboratory, fume hoods remove a volume of air equal to the volume of the room within 6 minutes. (In other words, the air in a laboratory is exchanged 10 times per hour.) As a result, large volumes of fresh air are continually re-supplied to these laboratories. The heating and air conditioning systems that supply this fresh air consume significant quantities of steam and chilled water from the Charter Street utility plant. In addition, the fans that provide fresh air and fume hood exhaust consume large amounts of electricity. (The Chemistry building is the 2nd largest user of electricity on campus - only the hospital uses more. Heating our building during the winter requires 1.5 rail cars of coal per week.) In terms of energy efficiency, our buildings employ heat-recovery systems to re-capture a portion of the heat content from the fume hood exhaust before the air is ejected from the building.
The exhaust systems in both the existing building and the new addition are designed to provide a constant volume of exhaust air. As described above, the volume of exhaust air does not depend critically on sash position. Quite honestly, the energy efficiency of a "constant volume" exhaust system is not strongly correlated with fume hood sash position. The compelling justification for lowering your fume hood sash is SAFETY.
At some point in the future, many of you will work in laboratories equipped with a "variable-air-volume" (VAV) exhaust system. In contrast to a constant volume exhaust system, the energy efficiency of a VAV system is directly related to sash position: the sash position is used to control the volume of supply and exhaust air in such a way to maintain a face velocity of 80-100 linear feet per minute.
Maintenance
The University has made great strides in improving the airflow in the Chemistry Building. Many fans and heat exchange coils have been replaced and plans have been drawn for further improvements. Temporary fume hood volume reductions and shut downs are a fact of life as the University Physical Plant and outside contractors work on the building ventilation systems. Researchers have a responsibility to themselves and their coworkers to pay attention to announced alterations in hood efficiency and to suspend fume-producing chemistry during periods when the hoods cannot be relied upon to exhaust fumes safely.
