The importance of chemical fume hoods cannot be understated, nor can the importance of safety protocols when dealing with these devices.
According to Mark Lee, Assistant Professor of Radiology and Chemistry at the Univ. of Missouri, there is one crucial piece of lab equipment that determines if a room is a just a room or a chemistry lab—the chemical fume hood. Lee depends on five 8 ft hoods in his chemistry lab to keep his research team safe as they increase the potency of cancer drugs, one molecule at a time. Without the development of fume hoods and the ability to keep scientists safe while working with hazardous or toxic chemicals, science would not have evolved into what it is today. Chemical fume hoods are prevalent pieces of lab equipment located in university science buildings all over the world.
Chemical fume hoods are an important part of any lab activity involving hazardous chemicals. They began as a simple fireplace chimney where hazardous chemicals were drawn out of a room by the natural draft created within the chimney. Fume hood design and performance has greatly advanced since then with new models that increase containment while reducing face velocities. A decrease of required face velocity results in a reduction in the operating cost of a fume hood. The typical annual cost of operating a 6 ft constant volume fume hood is $8,750/yr or $131,250 over the lifetime of the hood. The operating costs vary depending on the climate and the amount of tempered air that is required by the fume hood to operate safely.
Adding a fume hood in a room is only the first step needed to provide a safe environment for students and researchers. Ensuring adequate fume hood performance, proper personnel safety training and the adherence to safe lab practices while working within the hood, are all essential factors directly influencing the safety of students and lab personnel.
At some universities, the responsibility for fume hood operation falls under the Facilities Department, while others are covered under the EH&S (Environmental Health and Safety Department). Mike Russell, Director of EH&S, Univ. of Kansas (KU), indicated that his department performs ASHRAE 110 qualitative tests for more than 600 fume hoods on an annual basis to ensure proper hood performance. He has been in his department 21 years and believes the biggest change in fume hoods has been the arrival of high performance fume hoods. These hoods reduce operation expenses and increase user safety by improving fume containment while lowering face velocity requirements. KU has standardized on Labconco Protector XStream Fume Hoods with total variable air volume (VAV) exhaust systems running at a face velocity of around 80 fpm. Russell says he feels comfortable with the 80 fpm face velocity but will vary the number up or down depending on the lab layout and procedures.
Until recently, general thinking was that the more dangerous the chemical, the higher the face velocity required to ensure adequate protection for the operator. Face velocity is still regarded as an important parameter for assessing a hood’s performance; however, present views focus on containment also. The emergence and popularity of high performance hoods is evidence of this trend. Higher velocity is not necessarily better. A face velocity that is too high can cause turbulence within the hood and actually decrease the hood’s ability to contain contaminants. The newly redesigned Labconco Protector XStream Fume Hoods were designed to consume the lowest volumetric rate of air (cfm) regardless of the desired face velocity. For example, a 6 ft hood operating at 80 fpm with the sash at open 18" requires only 575 cfm, and at 60 fpm is only 430 cfm.
The two "S's"
Sustainability and safety are two of the concerns that Debbie Decker, Chemical Hygiene Officer at the Univ. of California, Davis, thinks of in regards to fume hood use at her university. One part of the fume hood she feels is critical to increasing safety and decreasing operation cost is the sash, more specifically, the sash height position. Decker has recently partnered with colleague Allan Doyle, Sustainability Manager at UC Davis, who has developed a sticker that is applied to the front of the fume hood that clearly marks where the sash should be positioned. The sticker is three zones—red, yellow and green—indicating optimum sash height positions. Doyle conducted assessment testing before and after the sticker application, and while results varied depending on the building, the application of the sticker resulted in an increase in proper sash height positioning with compliance increasing from 70 to over 90% almost immediately. During the next two years, the compliance increased even further, saving the university thousands of dollars a year.
“Close the sash” is a phrase Russell repeats on a daily basis. Leaving the sash up on a variable volume fume hood can be equivalent in tempered air loss to leaving 5 doors open to your house in the middle of winter. Labconco’s Intelli-Sash option automates the sash positioning by utilizing an adjustable sensor to close the sash when the work zone is empty and raise the sash to a user-defined working height when someone is in front of the hood. Not only does the lowered sash reduce airflow into the hood, it is also a physical barrier protecting end users from potential reactions as well as protecting their breathing zone. With the Intelli-Sash option installed on a fume hood, safety and sustainability are automated.
"The work area inside a fume hood is expensive real estate that should be used for procedures where protection of students is needed, not as a chemical storage area," Decker says. Waste bottles and chemicals should be stored in areas designated for proper chemical storage, not left in the fume hood. Air flow patterns within fume hoods are affected when objects are blocking the baffles and can actually jeopardize fume containment if conditions are severe enough.
Russell runs into this same problem and emphasizes that students employ good housekeeping within the hood. He sees experiments being set up and not being taken down before the next step in the procedure is started. “Fume hood clutter is a collection that is constantly being added to, but not being reduced,” says Russell.
In addition to fume hood clutter, other factors that affect the performance level of laboratory hoods that are not easily monitored by simple measurement of face velocity include: 1) type and location of air supply; 2) location of laboratory hood in relationship to the laboratory itself; 3) air disturbances caused by overhead air diffusers, heat registers, fans, open windows and doors, or personnel movement; 4) hood sash configurations; 5) location of the worker in relation to the hood; 6) location and types of emission sources; 7) apparatus loaded or stored in the hood; 8) use of apparatus such as machine tools, grinders or centrifuges that generate aerosols and/or high velocity particles; and 9) thermal drafts due to extreme temperature conditions.
Univ. of Missori’s Lee believes lab safety is in his DNA, but he doesn't believe that proper fume hood use or following safe lab practices comes naturally to students. In 2008, a tragic UCLA lab accident resulted in the death of a young research assistant, Sheharbano Sangji, and it had a strong effect on Lee. He had previously worked at UCLA in the lab located directly below the lab where Sangi’s accident occurred. He tells his students, “The two most dangerous times in a lab are when you are doing a technique for the first time and the 500 time.” According to Lee, taking safety training courses is just the first step. The enforcement of safe laboratory practices on a daily basis is a role he takes seriously and finds the most challenging, as there is a natural tendency to become more complacent as techniques become familiar and repetitive.
No doubt the use of chemical fume hoods has led to many scientific discoveries, contributing to an increase in the quality of life. More importantly, the researchers who have made these discoveries, many of which required hazardous chemicals, have been able to live long lives because of the safe working environments fume hoods have provided them.