Share thisLast month I started a series of columns to discuss sustainable design and containment. This month I will focus on energy issues particularly related to the systems required, and energy used, to move air through a containment laboratory. These factors make up a significant amount of the capital (design and construction) costs and operating costs for containment facilities. How much benefit do you get for increasing system performance beyond the minimum required for safe operation? As with most issues in containment, the answer depends on what you are using in the facility and how you are using it. One will likely get a very different answer in a laboratory utilizing primary containment from an animal holding suite with loose housed large animals infected with pathogens posing a high risk to the environment. In fact, this difference describes the crux of the issue. Primary containment whether it is a biological safety cabinet, containment cage, isolator, or other technology, creates a micro-environment where the agents are used. Providing sufficient airflow (directional and air change rate) to dilute and control the movement of pathogens within the device is generally accomplished by the primary containment systems basic design. In addition the relative volume of the device, as compared to the volume of the room it may be located in, is small enough that high enough air change rates and sufficient capture velocities are created within the normal parameters of system design.
Work analyzing the impact of air change rates in biological laboratories since the mid 1970s has shown that air change rates typical of laboratories (6 to 25 air changes per hour) are not particularly effective in reducing biological contamination to a safe level if aerosols are generated. True laminar flow or much higher air change rates would significantly reduce contamination; however, it would likely take air change rates in the range of 60 to 90 air changes an hour to achieve significant reduction of aerosol contamination in a reasonable amount of time. True laminar flow could be a strategy for rooms at a velocity of 90 to 100 feet per minute; however, when passed by the face of a Class II biosafety cabinet, this velocity would result in current Class II biosafety cabinet designs failing containment. That would be detrimental rather than a contribution to laboratory safety. Air change rates at these high levels would be cost prohibitive in both construction and operation as compared to other strategies.
The advantage of primary containment is that due to the significantly smaller volume in the primary containment device versus the room within which it is housed very high air change rates, can be achieved with a low impact on costs. The strategy of using primary containment with high air change rates and low air exchange rates in the room provides the correct benefits in both the room and primary containment device. Due to the high air exchange rate the dilution of aerosols in the primary containment envelope reduces potential aerosol exposure in the room if there is a failure of primary containment. Because of these factors, it is becoming more accepted that six to eight air changes provide an appropriate environment in a containment laboratory. Again, this relates to laboratory rooms and biological aerosols; if your issue involves an animal room and concerns involve reducing contaminants such as odors or dander to an acceptable threshold level higher air change rates may be more beneficial. My advice for sustainable design would be to understand what benefits you are receiving for arbitrary air change rates and to carefully balance these benefits against other options and the cost in both dollars and energy waste. Whatever the air change rates you settle on, consider installing a system to reduce them when the space is unoccupied. Typically laboratories are unoccupied over 50% of the time.