An Exhaust Solution for Controlled Environments
Mixed-flow impellers offer pharmaceutical plants enhanced safety, better plume dispersal, lower emission concentrations and reduced energy costs.
By John Gibson, MCIBSE, Associate Director, Scott Wilson Building Services
Most pharmaceutical manufacturers maintain controlled environment work areas for research, pilot production and, occasionally, for general product manufacturing. All of these facilities share an air quality challenge: exhaust from laboratory workstation fume hoods or other procedure/processing areas must be safely discharged into the atmosphere without causing re-entrainment, creating an odor problem or violating environmental regulations.
|Rooftop stacks, which can provide an undesirable but recognizable "signature" as to the procedures being conducted within the facility.|
Most pharmaceutical manufacturers also face high energy costs for their HVAC systems, and particularly for their conditioned, controlled environment facilities. Energy costs for pharmaceutical research and manufacturing are among the highest such costs for all standard industrial classification (SIC) categories.
Exhausting laboratory workstation fume hoods has traditionally been handled by centrifugal belt-driven fans with tall, individually-dedicated stacks or combined multi-stacks on the roof. However, mixed-flow impeller technology, with low-profile roof exhaust systems, has been gaining acceptance over the last few decades as a solution to exhaust cost and safety challenges.
Mixed-flow impeller roof fans send their exhaust streams hundreds of feet into the air in a vertical plume, diluting outside air with exhaust gases at the point of discharge. This highly efficient plume dispersal prevents local re-entrainment and, through high-efficiency mixing of the discharge air with the surrounding atmospheric air, eliminates potential odor problems at ground level.
Mixed-flow fan systems can also reduce unnecessary energy losses since they can pre-heat (and pre-cool) makeup air before it enters a building. This is achieved by the inclusion of heat transfer run-around-coils which capture exhaust heat and return it in a safe manner to the incoming air stream. This system permits substantial, safe, energy savings for research and manufacturing organizations.Exhaust stream dilution prevents re-entrainment
Roof exhaust systems’ main purpose is to prevent re-entrainment, to ensure healthy indoor air quality (IAQ) and conformity to local legislation. Should re-entrainment occur, there is a real risk to employees at pharmaceutical facilities due to exhaust re-entrainment through building intake vents, doors, windows and other openings. Re-entrainment can be caused by inefficient roof fans, poor design or location of exhaust stacks, position of building air intakes, weather and wind conditions, and a host of other factors.
However, the legal consequences of re-entrainment can extend well beyond employers. Building owners, consulting engineers, heating, ventilation, and air conditioning (HVAC) contractors and even architects have been named as defendants in major cases associated with employee illness and IAQ.
Research laboratories at most pharmaceutical organizations can range from discrete prototyping facilities through complex biosafety containment level (BSL) 3 or 4 facilities, which require accurate, repeatable control and management over such environmental parameters as temperature, pressure, airflow and humidity—almost always in combination.
While all BSL 3 and 4 laboratories have terminal HEPA filters, consideration of roof exhaust re-entrainment cannot be ignored as there is always the potential for filter failure and a highly efficient plume discharge is required during fumigation procedures.
Because high containment BSL laboratories present a unique set of problems with regard to re-entrainment and pollution abatement, they are governed by rigid pollution-abatement codes and standards promulgated by organizations that include the American National Standards Institute (ANSI), the American Society of Heating, Refrigeration and Air conditioning Engineers (ASHRAE), OSHA and CDC. In some cases, there are hard-and-fast codes, just guidelines and recommendations.Special exhaust requirements at BSL laboratories
Biosafety level laboratories of the containment levels 3 and 4 must incorporate special design and engineering features to prevent microorganisms from being discharged into the environment. These features would typically include specially shielded isolation rooms under negative pressure with high efficiency particulate arresting (HEPA), terminal filters, sophisticated control and monitoring systems for managing their environmental parameters; they would also require 100% conditioned “makeup” air to prevent the re-use of ambient air within an enclosed facility.
Obviously, exhaust emissions from laboratory workstations at these facilities must be treated carefully, including the discharge of fumigation gases. They may be highly toxic or noxious, or both. Even if the exhaust stream does not present health issues, the public will no longer tolerate annoying odors, while government agencies are continually setting more stringent standards and lowering allowable exposure limits.HEPA filter modules reduce dust emissions
In pharmaceutical research laboratories and pilot processing areas, a dedicated air supply and exhaust system is critical to safety as well as comfort. The HVAC system is typically independent of all other supply and exhaust systems within the building. Because of increasingly stringent environmental regulations, mixed-flow impeller systems incorporating bag-in/bag-out (BIBO) High Efficiency Particulate Arresting (HEPA) modules and filters are also being used for research, pilot plant and commercial manufacturing environments. The modules are typically matched with application-specific filter media which accommodate a variety of HEPA and ASHRAE filter efficiencies.