Douglas B. Walters, Ray Ryan, and Sai Kotha
Several articles appeared recently in Lab Animal News about the importance of bio-containment in the planning and design of animal laboratories1, 2,3. As these papers state the planning, design, construction and commissioning of these facilities is difficult and complex for many reasons. These reasons include complying with regulations and guidelines, accomplishing the work mission, identifying potentially hazardous agents, performing a risk assessment on the proposed agents and operations, providing an environment free from worker and environmental exposure, and doing all this within budget restraints.
This article describes recent advances in ventilation and hood design that significantly increase worker safety because containment is dramatically improved. At the same time tasks can be preformed better and more efficiently. In addition, initial purchasing costs are lower and because airflow is less and more efficient energy consumption is less resulting in substantial savings in utility costs.
Today’s Biomedical Containment Facilities
Today’s workers are more concerned with safety than ever before. The decrease in the OSHA Permissible Exposure Limit of formaldehyde over the past 20 years is just one of many examples of increased safety regulations. The laboratory use of potent, hazardous biological agents, chemicals, solvents, novel drugs, and substances of unknown and increasing toxicity are continually expanding. Many laboratory tasks previously done in the open are now performed in hoods and other specialized vented areas. Unfortunately, the ability of laboratory hoods to contain these hazards has not kept up with these increased hazards4, 5. Hoods and other ventilation devices are often poorly designed and have limitations, e.g., containment is often not effective, enclosures are not task-specific, relocation of hoods is complex, and hood purchase, installation and operation is expensive.
Containment: the Key to Performance
It was recently reported at an annual EPA Laboratory Design meeting that when thousands of laboratory hoods with face velocities between 80 and 100 fpm were evaluated for containment 17% failed to meet the tracer gas (SF6) control level of 0,1 ppm specified by ASHRAE 6,7. It was also reported that when 366 laboratory hoods were tested 51% met the face velocity requirement of 80 to 100 fpm but only 29% met the ASHRAE containment criteria 8.
Many laboratory and safety personnel do not realize that face velocity and the number of room air changes per hour have a poor correlation with hood containment. Both the American Industrial Hygiene Association and the American National Standards Institute have stated that face velocity alone is an inadequate measure of hood performance 9. The only proper measure of hood performance is containment. How well does the hood capture and contain the hazardous materials being used in the hood or vented enclosure?
CFD and MRI: the Tools of Visualization
It’s very difficult to visualize the flow of air in laboratory hoods, and vented enclosures. A new technique called Computation Fluid Dynamics (CFD) has radically changed laboratory hood technology. The application of CFD to laboratory ventilation and engineering controls is comparable to the application of Magnetic Resonance Imaging (MRI) in biomedical science. Just as MRI enables us to see inside the animals’ body it is now possible to see the behavior of air inside hoods and see how the hood will perform before it is built.
Figure 1 shows how CFD allows us to see the air flow structure inside a traditional laboratory hood. Different colors indicate different airflow velocities; red being the fastest and blue being the slowest. Notice the circular movement of the air, usually termed as eddy, inside the hood and behind the sash. It is this circular movement or roll that causes the containment problem in traditional hoods because it lets air escape from the hood at the hood face. The presence of a worker in front of the hood accentuates the problem. Similarly, cross drafts due to personnel traffic flow in front of the hood, or the proximity of a door, or an improperly located air diffuser in the ceiling further contribute to the loss of containment.
Figure 2 shows a vented enclosure specifically designed for weighing. Figure 3 shows a CFD representation of the vented enclosure in Figure 2. By using CFD the vented balance enclosure workstation design could be optimized to maximize containment and to minimize the amount of air necessary to achieve containment. The roll behind the sash is displaced away from the front opening of the enclosure and is reduced in size to insure that air does not escape at the hood face and containment has increased.
Independent testing has shown that properly designed vented enclosures can meet and actually exceed the ASHRAE 110 standard. Flow Sciences International (FSI) is the world leader in the innovative design, and manufacturing of properly engineered, task-specific, vented workstations. All FSI’s vented enclosures meet and exceed the containment requirements of the ASHRAE SF6 standard. In addition, all their products are tested using surrogate powders like naproxen sodium and lactose because these substances have a lower detection limit. Independent, third party testing has shown FSI’s vented workstations not only exceed the ASHRAE SF6 0.1 ppmcontainment limit, but shows containment to 5 ng/m3 using surrogate powder testing! This data is available on the FSI website (www.flowscienes.com).
Animal Laboratory Applications of Task-Specific Ventilated Workstations
Task-specific vented workstations have numerous applications in animal science laboratories. These applications include weighing and handling hazardous agents, animal dosing, necropsy, tissue trimming, reagent preparation, e.g., formaldehyde and xylene dispensing, and other histopathology techniques like cover slipping, staining, etc.
Figure 4 shows a vented enclosure designed specifically for a microscope. Figure 5 shows a CFD representation of the airflow inside the microscope enclosure in Figure 4. Figure 6 is a vented anesthetic containment enclosure. Figure 7 is a vented robotic enclosure typical of those used to contain high-throughput automated equipment in which hazardous agents are used. The applications are limitless. For example, work is actively underway on the design of a new cage dump system.
In addition to dramatically improving containment, these enclosures are ergonomically designed for long-term worker use during large sacrifices, are less expensive to initially purchase than traditional laboratory hoods.
A further advantage is realized in energy conservation. Because CFD optimized the airflow containment is accomplished using much less air. This means less energy is used, which results in considerably lower operation costs. For example, a standard 6 foot laboratory fume hood operated 24/7 uses about 1200 cfm and costs ~ $6,000/year to operate10. Animal science laboratories use a large amount of ventilated equipment; most of which is frequently not designed to be energy efficient. Ventilated workspace in animal science laboratories is typically not constructed in an energy efficient manner and the amount of air used is often excessive, hence, the utility costs can be high. As a rule of thumb 1 cfm of air cost about $5-7/year. Because a 4 foot vented workstation uses only about 175 cfm and costs ~ $900 to operate, use of properly designed; energy efficient vented enclosures can dramatically decrease utility costs. .
As you can see hoods have come a long way in recent years. Control of hazards is more that simply enclosing the problem. The real questions that should always be asked are how well do the ventilated areas contain the hazards and are the workstations really suitable for the tasks being performed.
- Crane J. Perspectives on Containment. Animal Lab News 2005; 4:50-56
- Crane J, Richmond J, Kreitlein S, Ferries R, Bressi S. Highly Pathogenic Avian Influenza (HPAI) Facilities. Animal Lab News 2006: 5:15-22
- Crane J, Kreitlein S. Perspectives on Containment. Animal Lab News 2006; 5:49-52
- Kolesnikov A, Ryan R, Walters DB. Task-Specific Ventilated Robotic Enclosures for Product and Worker Protection Against Biological Hazards in High-Throughput Laboratories. Applied Biosafety 2004; 9:188-199
- Kolesnikov A., Ryan R, Walters DB. Use of CFD as a Risk Assessment Tool to Help Determine Airflow Distribution and Concentration of Laboratory Contamination. American Biological Safety Association, San Antonio, TX, October 2004
- Hitchings DT. Commissioning Laboratory Fume Hoods Using ASHRAE 110-1995 Test Methods. EPA Labs for the 21st Century Conference, Cambridge MA Sept. 8-10, 1999
- American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE). “ Methods of Testing Performance of Laboratory Fume Hoods.” Standard 110 (1995), Atlanta GA
- Smith T, Crooks S. Implementing a Laboratory Ventilation Management Program. Chemical Health and Safety. 1996; 312-16
- American National Standards Institute (ANSI). “Laboratory Ventilation Standard-2004”, American Industrial Hygiene Association, Fairfax VA
- Smith T, private communication, ECT Technologies, Cary NC
Douglas B. Walters, Ph.D., CSP is the former Director of Laboratory Health and Safety for the National Toxicology Program (NTP) of the National Institute of Environmental Health Sciences (NIEHS/NIH) in Research Triangle Park NC. He is the president to of KCP Inc. a consulting company in Raleigh NC specializing in laboratory and chemical health and safety. He is internationally recognized in the field with over 150 publications including 27 books.
Ray Ryan is the President and CEO of Flow Sciences Inc., Leland NC (1-800-849-3429; www.flowsciencews.com). FSI pioneered the innovative design of vented enclosures that have been used extensively for almost 20 years in the pharmaceutical industry for containment of hazardous materials. Mr. Ryan is a chemist/engineer has lectured internationally and holds numerous patents on his designs.
Sai Kotha has a Masters degree in mechanical engineering with a focus in computational fluid dynamics and a bachelor’s degree in mechanical engineering and is the Computational Fluid Dynamics engineer at Flow Sciences Inc responsible for the air flow modeling. He has presented his work in various conferences and technical papers.