Task-specific ventilated enclosures are now available for the containment of hazardous laboratory operations and materials. These enclosures are designed to augment and complement existing, traditional laboratory hoods and have the distinct advantage of being extremely energy-efficient so that energy utility costs can be reduced as much as 90%. In addition, these new engineering controls are ergonomically designed to meet specific laboratory needs.

Task-Specific Vented Enclosures

Task-specific vented safety enclosures are safety containment devices that provide enclosed work areas where the handling of potentially hazardous substances can be performed with minimal risk to users and also provide product protection. These enclosures are used extensively in numerous pharmaceutical, chemical, biological, clinical, and toxicological laboratory facilities in industry, government, and academia. Figure 1 shows a sample cross-sectional schematic. Vented workstations are custom tailored to meet the demands of many applications such as weighing, chemical transfer, pipetting, microscopy, histopath-ology, and even mailrooms (Figures 2 and 3). Most recently vented enclosures have found widespread use in the pharmaceutical industry for use with robotic and high-throughput technology and for the weighing of bulk powders in the pharmaceutical industry (Figure 4). Flow Sciences uses computational fluid dynamics (CFD1) to optimize workstation design to maximize containment of hazardous contamination and, thereby, maximize personal and product protection.

A Complement and Alternative to Traditional Laboratory Hoods

Many laboratory operations and processes can only be safely performed using large, traditional laboratory hoods. Many tasks previously done on the open bench have been moved into hoods because of increased safety awareness and regulations.2 But laboratory hoods have many limitations, (e.g., containment is not always effective;3,4 large space is required; they are not task-specific; hood relocation is difficult; purchase, installation, and operation is expensive;5 and they are increasingly complex6-8). Similarly, the quantity, chemicals, and methods used in laboratories are constantly changing. Smaller amounts and less hazardous chemicals are used when possible. High-tech methods like combinatorial chemistry decreased dependence on traditional laboratory experimentation9. Finally, corporate restructuring frequently relocates and reorganizes laboratory work so that large hoods don’t always meet the needs of today’s dynamic laboratories.

In contrast to traditional laboratory hoods, vented enclosures are custom designed for specific tasks so that much less air is required. This results in energy-efficient, low-cost, alternative workstations that supplement and complement laboratory hoods. These smaller, precision-engineered enclosures are tested and validated so that less air at lower face velocities is used to provide laminar flow that produces minimal turbulence. This means there is better containment, less noise and vibration, and a corresponding major energy reduction and significantly lower operating costs.

Containment - The Bottom Line

Understandably, most scientists know little about how hoods function. They assume that as long as the operating light is on or the motor can be heard, the hood is working properly. Similarly, laboratory workers and safety professionals often don’t realize that face velocity and room changes per hour correlate poorly with hood containment.10 When thousands of laboratory hoods were tested using the ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) 110 test,11 it was reported that an average of 17% failed to meet the tracer control capture containment level of 0.1 ppm.3 In addition, when 366 laboratory hoods were tested, 51% passed the face velocity criteria, but only 29% met the ASHRAE 110 criteria.4

The design goal of an efficiently operating enclosure is to:

• Maintain the highest level of containment control

• Provide stable airflow environment for sensitive equipment inside the work area

• Ensure materials inside the enclosure are undisturbed by airflow

Computational Fluid Dynamics

CFD uses a sophisticated, mathematical modeling analysis system to predict and optimize the airflow velocity and flow field distribution in laboratory vented enclosures.1 This technique permits containment to be maximized while minimizing turbulence and allowing for a smooth transition of airflow inside the enclosure. Hence, air moves unperturbed and horizontally across the work surface. The resulting laminar flow promotes containment efficiency without affecting instrument reading or dispersing light powders or otherwise compromising efficiency.

Figures 5a, 5b, and 6 show a vented enclosure and traditional laboratory hood, respectively, with the velocity vectors colored by velocity magnitude in meters per second. The flow enters the room from the right and proceeds to enter the hood at the sash opening. The flow then exits the main hood chamber through the slot exhausts at the rear of the hood and the room through the exhaust at the top of the hood plenum. The main flow structure in experimental smoke test observations as well as computer-predicted numerical simulations is a large vortex (i.e., roll) behind the bottom of the sash. This has been identified and reported in several publications.12,13 These reports show that the presence of this large-scale reverse flow region in the immediate vicinity of the user work-area prevents efficient operation of a hood by causing hazardous materials to leak from behind the sash into the area occupied by the laboratory worker.

CFD enables scientists to modify the top airfoil and minimize the roll so that there is no reversal flow behind the sash door and, hence no loss of containment, as shown in Figure 7.

Validation

Independent studies by pharmaceutical companies and some we have conducted14,15 confirm that their vented enclosures consistently outperform all others. Testing, using a modified ASHRAE 110 protocol with SF6 (sulfur hexafluoride), verifies that our vented enclosure contains well below the 0.05 ppm detectable limit of the test. Indeed, breathing zone monitoring using sodium naproxen as a particulate marker chemical shows that the vented balance safety enclosures (VBSE) for bulk potent powders consistently contain below 5 ng/m3 of air.15 Such containment is possible because toxic emissions are controlled at the source.

Energy Savings

Vented workstations are usually connected directly to the existing laboratory exhaust ventilation system by a four or six inch duct. Depending on the HVAC system, enclosures can be installed, relocated, or removed quickly to adapt to workplace changes. A six foot laboratory hood operating 24 hr/day requires approximately 1200 cfm of air, whereas a four foot vented workstation uses only approximately 175 cfm. This means seven vented enclosures are equivalent to one laboratory hood in air consumption and provide five times as much vented bench space. Until recently, 1200 cfm costs approximately $5000/year.3,16 Additionally, vented enclosures usually cost 80% less than laboratory hoods, and are easier and cheaper to install. For nonvolatile particulate applications, air can be passed through bag-out HEPA filters, monitored, and recirculated.

Summary

A landmark conference at the Howard Hughes Memorial Institute in Maryland17 described what is needed to improve the effectiveness and performance of laboratory ventilation and hoods. We are continually working to address those needs.

References

1 A. Kolesnikov, R. Ryan, and D. B. Walters. “Use of CFD to design containment systems for work

withhazardous materials,” Chemical Health and Safety, Vol.10, No. 2 (2003) pp. 17-20.

2 U.S. DOL OSHA Standard for Occupational Exposure to Toxic Substances in the Laboratory (The

Laboratory Standard). 29 CFR 1910.1450.

3 T. Smith, S. Crooks. “Implementing a laboratory ventilation management program,” Chemical Health and Safety, Vol. 3, No. 2, (1996) pp. 12-16.

4 D. T. Hitchings. “Commissioning laboratory fume hoods using ASHRAE 110-1995 test methods.” Presented at the EPA Laboratories for the 21st Century Conference, Cambridge, MA, (Sept 8-10,

1999). www.epa.gov/labs21century/conf/conf2000/index.htm.

5 G. Bell. “A design guide for energy efficient laboratories.” Presented at the EPA Laboratories for the 21st Century Conference, Cambridge, MA, (Sept 8-10, 1999). www.epa.gov/labs21century/conf/conf2000/index.htm).

6 J. Koenigsberg. “Laboratory ventilation and VAV technology,” Chemical, Health and Safety, Vol. 3,No. 2, (1996) p. 10.

7 G. P. Sharp. “How airflow control affects laboratory safety,” Chemical Health and Safety, Vol. 3, No. 2 (1996) p. 11.

8 E. L. Gershery, A. Wilkerson, R. V. Joao, C. E. Volin, E. Party. “Chemical hood performance: standards, guidelines, and recommendations,” Chemical Health and Safety. Vol. 3, No. 6, (1996) pp. 32-39.

9 E. K. Wilson. “Chemists turned visionaries.” C&EN, Vol. 78, No. 17, (2000) pp. 39-45.

10 American National Standards Institute (ANSI). “Laboratory Ventilation Standard,” (2004).

11 American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE). “Method of Testing Performance of Laboratory Fume Hoods,” Standard, 110, (1995).

12 A. T. Kirkpatrick, R. Reither. “Numerical simulation of laboratory fume hood airflow performance,” ASHRAE Trans., Vol. 98, No. 15, (1998) pp. 1-13.

13N. S. Lan, S. Viswanathan. “Numerical simulation of airflow around a variable volume/constant face velocity fume cupboard,” AIHAJ, 62, (2001) 303-2.

14 T. Smith. “Test results on Flow Sciences, Inc. 2 foot and 4 foot workstations,” Exposure Controls Technologies, Inc., Raleigh, NC, (March 25, 1994).

15 W. Woroniecki, T. Bryning. “Industrial hygiene report of surrogate material air monitoring survey of Flow Sciences vented balance safety enclosure for bulk powder weighing,” SafeBridge Consultants, Inc., Mountain View, CA, (Oct 30, 2000).

16 Laboratory control and safety solutions applications guide. Semens Building Technologies, Inc., Landis Div., Buffalo Park, IL, (1999).

17 L. DiBerardinis, et al, “Report of the Howard Hughes Medical Institute’s workshop on the performance of laboratory chemical hoods,” AIHAJ, 64, (2003) pp. 228-237.