By: K. Lee Stone Fume Hood Safety

As I walk through our laboratories on campus I continue to find laboratory personnel improperly using fume hoods. Just as with any device, for it to work properly you must use it properly. For example, you don't expect your house to heat properly if you have boxes sitting on all of your floor registers blocking the airflow or you don't expect your car window to protect you from the wind while

Lee Stone has a driving down the interstate if the window is rolled all the way down. I Master's degree in am sure you also would not expect your fireplace to contain the smoke toxicology from if a lit log is hanging out of the fireplace just as you don't expect your Indiana University and is a certified heating bill to be cheap or your furnace to operate efficiently if you Chemical Hygiene leave the front door open in the winter because you don't want to have Officer. Lee has to keep opening and closing the door. served as the Laboratory Safety I have summarized the most common mistakes below. Manager for the Office of Environmental Crowded Fume Hood Health and Safety since 2004. A fume hood, like the one in the photo below, that is over crowded with materials will not contain vapors, period. E-mail Lee Stone at: [email protected]

Just like materials blocking floor registers if you fill your fume hood full of materials it blocks the air flow which is being pulled through the face of the hood via a fan on the roof pulling the air through the back baffles of the hood. When the hood is full of bottles, equipment, boxes and other materials the air must move around all of these objects and then out the baffles. Once the hood is full or the baffles become blocked then the face velocity drops and the fume hood loses containment.

The only materials inside of the hood should be those that are actively in use. Don't block the baffles or use your fume hood as a chemical storage area or fill it full of unused materials as the more items in a fume hood the less efficient it will operate.

Improper Fume Hood Sash Height All of our fume hoods on campus are certified annually. Once the hood has been certified a certification sticker (shown below) is placed on the hood. This sticker indicates the average face velocity, the inspection date and the maximum safe operating height for the fume hood sash is indicated with a black line.

The fume hood sash should not be raised above this line while actively using the hood because just like the car window in the example the larger the opening the less efficient the fume hood will operate and when the sash is raised above the Maximum Safe Operating Height then the food will not function properly and you can lose containment. The sash not only serves the purpose of containing vapors but is also made of tempered safety glass which can act as a shield to protect you from projectiles and shrapnel should something rupture inside of the hood. The fume hood sash should be raised to a height in which you can comfortably work in the hood but not above the Maximum Safe Operating Height as indicated on the certification sticker.

Failure to Work at least 6 Inches Inside the Face of the Hood Just as a fireplace will not contain the smoke when a log rolls out of the fireplace, a fume hood will not contain vapors when materials are opened at the face of the hood. You must work at least 6 inches inside the face of the hood. Materials located less than 6 inches inside the face of the hood can be exposed to eddy currents which are generated by pulling your hands out of the hood, walking by the hood and other air disturbances in the laboratory. These eddy currents are moving opposite of the air flow into the hood and vapors can escape when trapped in the eddy currents. The illustration above demonstrates the air flow into the hood and the formation of eddy currents within 6 inches of the face of the hood. Once the material is located 6 inches or more inside the hood then a protective barrier is formed and the exhaust velocity is greater than the eddy current velocity and containment is maintained.

Failure to Keep the Fume Hood Sash Closed when not in Use

Similar to leaving your door open to your house, leaving a fume hood sash open when not in use is a tremendous waste of energy. A sash left open can consume the equivalent energy required to heat and cool over 3 average size homes on an annual basis. A closed fume hood sash serves many purposes. When the sash is closed it acts as a barrier between you and the materials that may be in the hood. The sash is made of tempered safety glass and can offer added protection from shattered glass, chemical spills, and vapors which will remain contained in the hood if the sash is closed when an "accidental event" occurs. In case of a power outage or hood ventilation failure, chemical vapors will not back up into the laboratory. If there is an accidental or emergency shutdown of the fume hood ventilation system a closed sash will help contain vapors in the hood. Never open a fume hood if the ventilation system is not operational. Energy savings. Most fume hoods at IUPUI operated on a "variable air volume" system, which means the volume of air exhausted is reduced as the sash height is lowered. Save energy and improve the safety of your laboratory by ensuring proper use of your fume hood. It is a Win-Win Solution.

Lab Notes is a quarterly publication by the IUPUI Office of Environmental Health and Safety. Lab Notes is designed, edited and published by K. Lee Stone. "Don't Learn Laboratory Safety by Accident!"