Establishing & Maintaining Workspace Parameters in Labs by Stephen J. Davis
The threat of global bioterrorism is unnerving enough, but now we also have SARS (severe acute respiratory syndrome) to worry about. It has already extracted a heavy toll on people, organizations, and economies on virtually every continent, and while a cure will no doubt be developed, chances are we will confront another, similar threat sooner or later. In fact, an ominous series of articles published in April in the Washington Post describes the South African government’s secret bioweapons program of the early 1980s in which scientists were developing pathogens as “weapons for terrorism and assassination.” (One scientist actually tried to sell these deadly agents to the American government for $5 million!)
As such, it is no wonder there has been such an exponential growth of biosafety-level (BSL) laboratory facilities at universities, as well as government and private research organizations, around the world. Like the Sword of Damocles,1 we are likely to remain under constant threat of chemical or biological weapons of mass destruction (WMDs).
BSL lab specifications and standards
Virtually all design and construction considerations for research laboratories (some of which are also known as ‘containment’ labs) are called out in specifications and standards published by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). Depending on the type (or biosafety level) of a facility, other organizations may also set appropriate standards, including the American National Standards Institute (ANSI), the Center for Disease Control and Prevention (CDC), the National Institutes of Health (NIH), U.S. Department of Health and Human Services (DHHS), and the American Society of Mechanical Engineers (ASME).
Each of these organizations is responsible for different sets of standards, depending on their specific areas of expertise and interest. Two of the major considerations involved with BSL labs are indoor air quality (IAQ) and atmospheric pollution, especially toxic, noxious, and/or odoriferous workstation exhaust. Among the specifics covered within the broad categories are safety issues (for people in and around the facility) like workplace contamination, and environmental parameters, such as heating, cooling, airflow, pressurization, workstation exhaust re-entrainment, and toxic/hazardous exhaust.
Many research facilities, like those at universities and pharmaceutical, biotech, and chemical/petrochemical organizations, must be designed to eliminate all possibilities of danger to workers or contamination of experiments. To accomplish this, most BSL labs are constructed as ‘once-through’ facilities, requiring 100-percent make-up air introduced into the workspace a specific minimum numbers of times depending on the level (standard) of the laboratory (see “Biosafety Level Laboratory Requirements”).
Tests and standards for closed environments
In these kinds of facilities, critical environmental parameters like pressure, temperature, humidity, and airflow must be precisely controlled and monitored for safety and security. ASHRAE’s Fundamentals Handbook refers to these facilities as “clean spaces.” Included among them are the cleanrooms used in industries such as pharmaceuticals, electronics, food processing, medical device manufacturing, advanced materials research, and automotive (paint spray booths).
While not associated with biotech research, cleanrooms at these facilities are nonetheless subject to many of the same standards relating to the accurate control and monitoring of their ‘closed environments,’ though maybe at different levels or standards. Even hospital operating rooms may be classified as cleanrooms, yet their primary function, says ASHRAE, “is to limit particular types of contamination rather than the quantity of particles present.” In its literature, ASHRAE says cleanrooms are also used in patient isolation and surgery “where risks of infection exist” (Chapter 7-Health Care Facilities).
ASHRAE is explicit in its recommendations for closed environment facilities. In Chapter 25-Nuclear Facilities of Handbook, the organization discusses air pressure considerations which “must be maintained slightly negative with respect to adjoining areas.” It mentions common methods of room pressure control, including manual balancing, direct pressure, volumetric flow tracking, and cascade control. All methods modulate the same control variable: supply airflow rate. However, each method measures a different variable.
To control the variables of temperature, airflow, and humidity, the room (or workspace) must be pressurized. This enables all other environmental parameters to be precisely controlled and monitored so as to achieve and maintain a contamination-free environment.
Pressurization standards are also covered in ASHRAE’s Refrigeration Handbook through ASHRAE 41.3, Standard Method for Pressure Measurement, and ASHRAE 41.1, Standard Method for Temperature Measurement. The refrigeration handbook discusses temperature measurement in conjunction with ASME PTC (Performance Test Code) 19.3, Temperature Measurement. It also covers the NFPA’s fire prevention codes under NFPA 45, Standard on Fire Protection for Laboratories Using Chemicals, and associated fire protection standards, including fire resistance testing for ventilating ducts. Finally, it includes the uniform fire code for ventilating ducts (International Organization for Standardization [ISO] 6944, Fire Resistance Tests:Ventilation Ducts), and the International Conference of Building Officials’ (ICBO’s) Uniform Fire Code.
Controls used in closed facilities for managing space pressurization and other environmental parameters are addressed in ANSI/ASHRAE 114, Energy Management Control Systems Instrumentation. Temperature control systems are also addressed by the Associated Air Balance Council (AABC) CH12, National Standards for Total System Balance (2002), as well as within separate categories (such as commercial and industrial) at the National Electrical Manufacturers Association (NEMA) and ANSI, Underwriters Laboratory (UL), AABC, and ASHRAE.
ASTM International also publishes procedural standards for certifying the testing of cleanrooms. These standards govern the continuous sizing and counting of airborne particles in dust-controlled areas and cleanrooms using instruments capable of detecting single submicrometer and larger particles (ASTM F 50, Standard Practice for Continuous Sizing and Counting of Airborne Particles in Dust Controlled Areas and Clean Rooms Using Instruments Capable of Detecting Single Sub-Micrometre and Larger Particles).
Both ASHRAE and ASTM publish test methods for determining air leakage rates by fan pressurization in enclosed facilities, as well as through exterior windows, curtain walls, and doors under pressure and temperature differences. Since air filters are critical in virtually all controlled environment facilities, a number of organizations publish independent specifications and standards for specifying and/or testing air cleaning devices for removal efficiency by particle size. Among them are ANSI/ASHRAE 52.2, Method of Testing General ventilation Air Cleaning Devices for Removal Efficiency by Particle Size, and UL 586, Standard for High-Efficiency, Particulate, Air Filter Units.
BSL laboratory facility classifications
In the United States, BSL labs are classified by the DHHS, CDC, and NIH into four levels (Biosafety Levels 1-4), and listed in DHHS standards. Following is a brief description of each of these levels according to ASHRAE’s 1999 Applications Handbook:
Biosafety Level Laboratory Requirements
Biosafety-level (BSL) laboratories are graded from 1 to 4, with standards set by a number of bodies, including ASHRAE, ANSI, the CDC, and ASME. These organizations set guidelines identifying and listing specific agents and the class of laboratory required for their use. Within each of the levels, there may be further defining criteria, depending on the type of work being conducted, the degree of hazard associated with that work, and other factors. Blood-borne pathogens like the AIDS virus generally require a Level 2 laboratory when research is handled in a clinical setting. However, when a laboratory is growing large quantities of the AIDS virus for study, it may be required to be a Level 3 facility. Level 3 also sees activity from agents such as tuberculosis and anthrax, as they are readily transmitted by aerosol generation. Microorganisms like bacteria can carry fairly serious consequences, and are also typically found in Level 3 labs. Level 4 is generally reserved for the study of the most exotic of sicknesses and viruses, such as hantavirus, hepatitis, and influenza viruses, and strains of viral hemorrhagic fevers, such as the ebola and Marburg viruses, and Lassa Fever.
These laboratories are suitable for work involving agents of no known hazard or minimal potential hazard to lab personnel and the environment. The lab is not required to be separated from general traffic patterns in the building, and work may be conducted on either an open benchtop or in a chemical fume hood. Special containment equipment is neither required nor generally used. The lab can be cleaned easily and contains a sink for washing hands. Federal guidelines for these spaces are usually acceptable. Many universities and research institutions require directional airflow from the corridor into the lab, chemical fume hoods, and approximately three to four air changes per hour of outside air.
These facilities are “suitable for work involving agents of moderate potential hazard to personnel and the environment. ” A list published by DHHS (1993) explains various levels of containment needed for hazardous agents. Biological safety cabinets are required in many cases, depending on the substances being employed and their concentrations or volumes. At this level of biohazard, most research institutions would have a full-time safety officer (or safety committee) for establishing standards. While federal guidelines for BSL 2 laboratories do not contain specific HVAC requirements, ASHRAE lists typical design criteria, including the following:
Level 3In these facilities, work done with indigenous or exotic agents may 3 laboratories use a physical barrier or two sets of self-closing doors (airlock) to separate the lab work area from areas with unrestricted personnel access. This barrier enhances biological containment to within the lab. Specifications are provided for the kind of ventilation system required as well as the necessary alarms, supply and exhaust duct work, and the possible requirement for HEPA (high efficiency particulate arrester) filtration, along with instructions for its use).
Laboratories handling serious and potentially lethal diseases transmittable via inhalation must conform to BSL 3 standards. They are also defined for bacterial, fungal, parasitic, and viral agents, and include more virulent and toxic forms of otherwise BSL 2 materials.
Level 4These laboratories are required for work with dangerous and exotic agents posing a high risk of aerosol-transmitted laboratory infections and life-threatening diseases. ASHRAE’s Applications Handbook points out the “design of HVAC systems for these areas will have stringent requirements that must be determined by the biological safety officer.”
Biosafety Level 4 agents are considered typical of what could be expected of a biological WMD. According to the list of infectious agents, these materials require the most stringent conditions for their containment, are extremely hazardous to lab personnel and can cause an epidemic. Not only are facilities and equipment critical in the operation of BSL 4 laboratories, but guidelines also call for “staff with a level of confidence greater than one would expect in a college department of microbiology, and who have had specific and thorough training in handling dangerous pathogens…”
These facilities are categorized as either ‘suit’ labs or ‘glove box’ labs. The latter usually contain Class 3 biological safety cabinets, and the entire laboratory is housed inside a solid perimeter wall serving as a physical barrier to keep microorganisms inside. Level 4 labs are not too common, with probably only a few dozen in use around the world. These facilities incorporate many special design and engineering features to prevent microorganisms from being discharged into the environment. For example, a dedicated air supply and exhaust system is critical to safety as well as performance at BSL 3 and 4 laboratories. The HVAC system is typically independent of all other supply and exhaust systems within the building; in other words, the air inside the research facility portion of the building must be fully conditioned and never re-used. In addition to conditioned make-up air, these facilities require safe and reliable methods of exhausting their workstations’ fume hoods to eliminate re-entrainment possibilities.
Applications Handbook (Chapter 13) contains detailed information on laboratory ventilation systems. It calls out the total airflow rate for labs, which is dictated by one of the following conditions:
The two basic types of airflow control for laboratories are constant-air-volume (CAV) and variable-air-volume (VAV). Applications Handbook contains full details on each of these technologies, along with their advantages and disadvantages. (Room pressure control is also discussed in this section [13.12]).
Since all BSL laboratory facilities require key environmental parameters to be precisely controlled (with predictable repeatability), room or work space pressurization is the first critical parameter to address. Without pressurization, it is virtually impossible to maintain precise and accurate control of other parameters (i.e., air temperature, airflow, and humidity) in an enclosed area. While ASHRAE calls out four different methods of achieving pressurization, the two most popular methods are airflow (volumetric flow), tracking, and differential (direct) pressure control.
Airflow tracking versus differential pressure
Controlling BSL lab pressurization using airflow tracking methods is based on the principle of measuring and controlling airflow in and out of a confined space. This method maintains the desired cubic-feet-per-minute (cfm) differential (offset) between supply and exhaust air, and permits precise airflow control, resulting in either positive or negative pressure, depending on requirements. Differential pressure directly measures the pressure difference from the enclosed work-space to a reference space (usually an adjacent corridor or an outside reference). Variable airflow control into the pressurized workspace is used to maintain a fixed level of differential pressure between the controlled space and the adjacent area.
Advanced instrumentation permits precise control
As with most technologies, both airflow tracking and differential pressure offer certain advantages, depending on the circumstances. The good news is each of these technologies is practical and easily achievable, thanks in large part to the development of new instrumentation capable of measuring extraordinarily low levels of differential pressure (typically in the region of 0.001-in. wc [water column]). To a large extent, inaccurate instrumentation in the past prevented the possibility of achieving space pressurization at desired levels (typically about 0.02-in. wc to past, pressurization levels were almost an order of magnitude higher, mainly because of limitations in both measurement devices and display instruments.
Lower levels of differential pressure are desirable for several reasons. Safety considerations dictate reasonable levels of differential pressure be maintained so doors may be operated properly and safely. For example, when a door opens inward and the space is at a high positive pressure, it may be impossible to open the door; conversely, when that space is under a high negative pressure, releasing the latch may cause the door to fling open, possibly causing injury to a person attempting to exit. Second, depending on construction, it is possible the pressurized space could implode, blasting ceiling panels downward where injury or equipment damage could occur. Third, to maintain accurate temperature control, it is desirable to minimize the quantity of air being infiltrated to, or exfiltrated from, the space.
From a technology standpoint, both airflow tracking and differential pressure control work to achieve the same objective; that is, to maintain the desired direction of airflow in and out of a space. However, certain factors must be considered when determining the best method for an application. The most important of these are architectural details and access to/from the controlled space(s).
Traffic flow and building architecture
The first consideration is access to, and traffic flow, in the lab. One must determine the area(s) accessibility to general spaces and exits from the facility. For example, is it located in a high- or low-traffic area? Will there be limited access to the pressurized space? Will airlocks be used? How many people will be involved in that space? Answers to these questions help determine the most suitable technology. For example, control is undesirable when the pressurized space is located in a high-traffic area because multiple upsets to the airflow create too many pressurization variations. Every change in the room or reference pressure causes the control system to respond and vary the airflow to or from the controlled space. One can also look at some of the general construction details in the facility to help determine whether the walls defining the space are contiguous, for example, from structure to structure, slab to slab, or floor to floor. The logic here is there should be no possibility of air migration from room to room above the ceiling. Essentially, the more one can isolate the controlled space, the easier it will be to successfully implement differential pressure control methods over airflow tracking (Table 1) The two main considerations, then, for determining the most viable air control method are architectural (building design and/or construction) and/or people movement and traffic.
Cascaded pressure control
A variation employing elements of both tracking and pressure control is known as ‘cascaded pressure control.’ This technique measures all supply and exhaust flows in and out of the laboratory, maintaining a fixed cfm differential between supply and exhaust air. Cascaded control adds the element of measuring differential pressure in the space as well, using that measurement as a reset point to the cfm offset. This allows the cfm differential to fluctuate between minimum and maximum values and respond to any influences affecting pressure. The advantage of this technology is it provides the stability of airflow tracking while allowing variable cfm differentials to meet temporary external conditions without sending the space out of control.
Differential pressure monitoringAnother variation finding use in certain applications is tracking with differential pressure monitoring. Here, airflow tracking is used as the control method and differential pressure monitoring is overlaid to function as an alarm set point and maintenance management point throughout the building’s ventilation system. For example, when a differential pressure measurement changes over time (other than when a door is opened or closed), it usually indicates one of two events occurred: either airflow was degraded on one side of the system (thus eliminating desired differential pressure), or there has been a change in the envelope. Someone may have opened a hole in a confining wall to install new piece of ductwork without proper sealing, or perhaps a pipe was installed through a floor and the resulting gap was not sealed. Cascaded pressure control techniques can be handy in these applications because they do not really add any complexity to an overall control scheme. Each of these control methods offers distinct advantages and disadvantages, depending on the application (level of biosafety), and each should be evaluated based on criteria including practicality for the circumstances (logical work flow/employee movement patterns, etc.) and cost- effectiveness (Table 2). One may wish to consider the kind of measurements necessary with differential pressure control and review its advantages and disadvantages (Table 3).
Adding other controlled environmental parametersHaving compared differential pressure with airflow tracking technologies, our attention turns to overall environmental control. In the critical environment of a BSL laboratory, there is generally a sequential hierarchy for most control requirements, starting with pressurization, then temperature, followed by humidity. The method of pressurization control selected has a direct bearing on managing these other parameters. For example, one can achieve the desired temperature in the laboratory to a very high degree of tolerance with airflow tracking; however, one could lose temperature control with differential pressure because the volume of air is being controlled by pressure requirements instead of temperature requirements. In essence, when pressurization control is the driving variable for the quantity of airflow in the space, all other control parameters may suffer as a result (with temperature usually being the first). For example, when one wants to maintain a space under negative pressure and is using differential pressure control, the supply airflow would vary to maintain pressurization. When a door is opened to that space, the first response from the system is to reduce the amount of supply air into the room so as to maintain negative pressure. The system response likely includes closing or reducing the supply airflow to zero to maintain the space at a negative pressure. When that occurs, temperature control is lost immediately. When supply air is used to maintain humidity control (and it almost always is) one loses control over humidity in the space as well.
When airflow tracking is the control method, the system will not respond to a door being opened. While pressurization is not maintained, the cfm differential remains the same. Consequently, one maintains the direction of airflow for pressurization purposes while maintaining temperature and humidity control— or overall environmental control. This is basically the only way to accomplish this level of control when those parameters are critical.
In most laboratories, one can expect to control temperatures to tolerances of ±0.556-1.11 °C (±1-2 °F). Humidity is more difficult to control and usually has a wider tolerance parameter, depending on environmental factors within the facility. Typically, a laboratory maintains humidity at 50 percent relative humidity (RH), but 40-60 percent is an acceptable deviation.
ConclusionWith increased interest and heightened awareness of the implications associated with bioweapons as tools for global terrorism, there is likely to be even greater growth in critical environment BSL laboratory facilities. Many products and systems are available for achieving and maintaining these environments on a practical, cost-effective basis. The important factor in implementation is selecting a supplier with a track record for the type of facility being constructed, and to use equipment and instrumentation designed for the job.
NotesDamocles once traded places with his friend, a king, who lived in constant fear for his life. He enjoyed the king’s lavish lifestyle for a day, but when he lay down to rest, he noticed a sword above his head— held in place by a single horse hair. Put there by the king, the sword taught Damocles what it was like to live in constant fear.
October 2003 The Construction Specifier