Beyond Traditional Biosafety

Biosafety professionals have ever-expanding roles at their institutions. In this Beyond Traditional Biosafety column, we focus on topics that may fall outside the scope of the traditional biosafety role but where the expertise of the biosafety professional may be called on to provide a valuable contribution to his or her institution. Please e-mail any comments, suggestions, or insights to William Wade at [e-mail].

Ventilation in a Research Environment

Ventilation is a key component for creating a productive, safe, and healthy working environment. In a research setting, it is an integral part of laboratory safety, and it contributes significantly to the comfort and productivity of the people and to the research activities being performed there. Despite the importance of ventilation, many researchers and research support staff may become aware of laboratory ventilation systems only when an issue arises, such as the presence of an odor or issues about thermal comfort. The objective of this article is to provide a general overview of the functions of ventilation systems in general laboratories. These systems may include the following:

Local exhaust ventilation (LEV) systems (eg, fume hoods, snorkel exhaust), which are designed to control employee exposure to airborne contaminants by capturing and containing contaminant sources and transporting them to a safe emission point or to a filter/scrubber

Supply air ventilation systems, which are designed to provide the overall heating and cooling requirements for the laboratory as well as the dilution ventilation so that contaminant concentrations are maintained within acceptable levels

In addition to the general design requirements and considerations for ventilation in the research environment, many institutions are putting a higher priority on energy efficiency in laboratories. Laboratory ventilation can be the most energy-intensive process in a research institution. ¹ As such, several energy-saving options are frequently proposed to make laboratories “greener”; these may or may not be conducive to proper laboratory ventilation.

Ventilation in Laboratories

The design of laboratory ventilation systems depends on a number of variables, which typically rely on both LEV (containment and capture ventilation systems) and general space ventilation to provide overall air dilution. The exhaust requirements for a laboratory are often considered first, given the larger airflow quantities required by fume hoods and/or other exhaust capture systems. Once the total laboratory exhaust rates are determined, the supply air quantities for the laboratory are determined to provide enough “makeup air” to almost match the exhaust and to ensure that the supply air rates are sufficient to meet the heating and cooling requirements for the laboratory.

From both an engineering and an environmental health and safety perspective, laboratory exhaust air systems are typically designed with “primary” and “secondary” containment in mind. For a laboratory space, the primary containment systems include the LEV systems (these are fume hoods for most laboratories). These systems are considered primary because they are often most effective at capturing and controlling point source pollutants generated in the laboratory space. The secondary containment is the laboratory itself, where contaminants generated in the laboratory are diluted and also contained from adjacent nonlaboratory spaces through the balancing of the laboratory air systems such that the laboratory is maintained at a negative pressure with respect to adjacent areas. In the ideal case, the majority of contaminants generated in the laboratory are captured through primary containment; however, factors such as large equipment and research activities not easily performed in a fume hood may require that higher dilution ventilation rates be provided in the laboratory.

Overall laboratory ventilation rates are typically expressed in terms of air changes per hour, which refers to the rate by which air is supplied or exhausted relative to the volume of the space. For general laboratory spaces, air exchange rates discussed in the literature often reference a range of 4 to 12 air changes per hour as being typical. However, when the air exchange rate for dilution is being considered, assessing the activities conducted in the laboratory (ie, chemicals, processes, and practices) is important to ensure that sufficient ventilation is maintained.

A typical laboratory supply and exhaust ventilation system configuration is as follows:

Outside air is drawn into an air-handling unit (AHU) through outdoor air intakes. Ensuring that outdoor air intakes are located away from potential odor or contaminant sources is important.

The air is conditioned (heated, cooled, humidified, and/or dehumidified) and filtered by the AHU.

The AHU delivers conditioned air to the laboratory through ducts, air terminal devices, and supply air registers.

The supply air passes through the laboratory space and is not recirculated.

The air exhausts out of the laboratory space via fume hoods and other exhaust vents located in the laboratory.

The air passes through exhaust ducts and fans, exiting the facility through exhaust stacks often located on the roof.

The design of the laboratory supply and exhaust air system is such that more air is exhausted from the laboratory than is supplied. Exhausting more air than that supplied ensures that the laboratory is maintained at a negative pressure with respect to adjacent nonlaboratory areas. This air balance ensures that the secondary containment requirement for the laboratory is maintained and that air from the laboratory is not transferred to adjacent nonlaboratory spaces.

Although laboratory ventilation systems are typically designed in accordance with best practices, these systems have the potential to contribute to negative indoor environmental quality issues, including the transfer of odors to areas served, thermal comfort problems, and unintended differential pressure changes between spaces. For example, in older buildings, it is not uncommon for outdoor air intakes to be located near potential odor sources (eg, loading docks and/or kitchen exhausts), which can result in the transfer of intermittent odors to the occupied spaces. Also, because laboratories are maintained at a negative pressure with respect to adjacent areas by design, they are potentially susceptible to direct air/odor transfer from adjacent nonlaboratory areas. Furthermore, unlike those in office spaces, where supply air diffusers are located to maximize mixing of air and thermal comfort, supply (makeup) air outlets in laboratories are positioned to maximize the effectiveness of the exhaust capture systems (not to maximize thermal comfort).

Biological Laboratories

As with general laboratories, ventilation systems in biological laboratories and tissue culture (TC) rooms provide several key functions, such as helping to ensure a safe and comfortable work environment and protecting the surrounding areas.

Biological research is conducted at 4 basic levels of containment: biosafety levels (BSLs) 1 through 4, with BSL-1 requiring the lowest level of containment and BSL-4 requiring the highest. BSL-3 and BSL-4 laboratories require specialized facilities with specific engineering controls and ventilation requirements, as outlined in Biosafety in Microbiological and Biomedical Laboratories, fifth edition. ² This discussion focuses on BSL-2 research space, the most common level of containment.

At BSL-2, ventilation should provide directional airflow to TC rooms, and the TC room should be negatively pressurized with respect to the surrounding spaces. The purpose of directional airflow is to provide an additional layer of containment to minimize the potential for biohazardous droplets and aerosols to be released from the TC room. Negatively pressurized rooms should be designed so that if a ventilation failure occurs, the room will stay negative or neutral to the surrounding space.

The number of air changes required for TC rooms depends on the occupancy and usage of the room. Most TC rooms use Class II A2 biosafety cabinets. Unless the cabinet is connected to a facility’s exhaust system through a canopy exhaust connection, Class II A2 biosafety cabinets exhaust HEPA-filtered air back to the room. Volatile and toxic chemicals should not be used in this type of cabinet.

Biosafety cabinets and other containment equipment are highly sensitive to air currents and airflow disruptions. As a result, ventilation should be designed to prevent excessive air turbulence around these devices. Also, appropriate equipment placement is vital to ensure that biosafety cabinets function correctly and to minimize the risk of the release of biological aerosols. Biosafety cabinets should be placed away from doors, fans, high-traffic areas, other biosafety cabinets and other areas with potentially disruptive air currents. In addition, the use of open flames in biosafety cabinets is strongly discouraged, as the heat can cause air turbulence and loss of containment and can damage the HEPA filter, allowing potentially contaminated air to be recirculated into the room.

Energy Use in Laboratories

The energy use in buildings with research laboratories is significant when compared with office or nonlaboratory buildings. For example, the energy cost to operate a typical chemical fume hood can be 3.5 times the annual energy use of an average American house. ³ This higher energy use is primarily due to the considerable volumes of supply and exhaust air required in these spaces, which are often operated 24 hours per day and 365 days per year. Also, because laboratory air supply systems deliver 100% outdoor air (air is not recirculated), the energy required to heat and cool the outdoor air is significant.

To reduce operational costs and the overall carbon footprint of a facility, facility managers in research buildings often implement energy optimization programs or studies. One option often considered is to convert the laboratory from constant air volume to variable air volume (VAV) control. Under VAV control, overall laboratory ventilation rates vary, depending on whether fume hood sashes are open or closed, while still ensuring that minimum required ventilation rates are achieved. When a VAV fume hood sash is opened, the supplied and exhausted airflows increase, and vice versa when the VAV fume hood sash is closed. Implementing this option often requires considerable engineering and hardware for laboratories with constant air volume (new air valves are often required) and is not a viable option for many facilities. As an alternative, a 2-position ventilation control strategy may be considered where maximum ventilation rates are maintained during occupied hours and reduced when the laboratory is not occupied. Energy savings may be realized for both these options.

In addition to overall ventilation rate reductions, incorporating heat recovery into the supply and exhaust air design significantly reduces the costs required to heat and/or cool the incoming air. These systems use the laboratory exhaust air to heat/cool the incoming air and are considered the norm in the design of new laboratory research buildings. Widening laboratory air temperature set points during unoccupied periods is also a common energy optimization measure and may be considered depending on laboratory thermal requirements. Again, the potential issue with the energy conservation measures discussed above is that in many research facilities, the buildings or certain laboratories remain occupied during “off hours.” Therefore, the use of occupancy sensors is critical to ensure that adequate laboratory ventilation rates are maintained when the laboratory and fume hoods are in use.

Conclusion

Proper ventilation has many applications for the health of a building and its occupants. Buildings that contain laboratories have more challenges than a typical office building. Multiple variables—such as the hazards associated with the research, the design of the building, the activity and occupancy levels, and the type and amount of equipment being used—must be considered to ensure that ventilation in the laboratory is adequate for workers’ needs and serves as a containment measure for laboratory hazards. Understanding the basics of laboratory ventilation is key to designing and maintaining a safe and comfortable laboratory environment.