FIGURE 1: A Class II Type A2 BSC.
Images courtesy of Salas O'Brien
Several years ago, I was contracted to perform an evaluation study for an existing biosafety level-3 (BSL-3) biocontainment laboratory on the West Coast. The lab was actively performing research on anthrax, tuberculosis, and other aerosolized pathogens. The facilities were 10 years old, and the client wanted the study to compare an existing lab facility assessment versus the latest National Institute of Health (NIH) Biosafety in Microbiological and Biomedical Laboratories standards as well as an evaluation of the existing facility condition with recommended repairs/replacement.
This article will provide an explanation on the biocontainment laboratory classifications levels, types of biosafety cabinets (BSCs) used in BSL-3 labs, NIH requirements for a BSL-3 lab, description of the BSL-3 lab being assessed, recommended procedures for performing a BSL-3 lab assessment, and what was discovered during the BSL-3 study. Though the study was comprehensive in evaluating the overall lab layout, architecture, security, electrical, HVAC, and plumbing; this article will focus on the HVAC systems.
FIGURE 2: A Class II Type B2 BSC.
Excluding animal biocontainment laboratories, biocontainment laboratories are classified as one of four levels. The more virulent and infectious the pathogen being worked on in the laboratory, the higher the classification level will be for the lab. It is important to know BSC are considered the primary barrier for containing the pathogen. The lab space and associated facility systems are considered the secondary barrier for containing the pathogen. The four levels have a hierarchy with all practices and procedures established on the lower level being carried over to the higher level. Descriptions of the four biosafety levels as follows:
BSL-4 lab requirements are more complex than those for BSL-3 labs. Exhaust systems require double-HEPA filtration. The HVAC and exhaust system need to provide a higher level of reliability. Typically, Class III BSC are used.
FIGURE 3: A BSL-3 laboratory floor plan.
There are three different classes of BSCs: Class I, Class II, and Class III. Within Class II, there are four types, including A1, A2, B1, and B2. In selecting a BSC, it is important to determine whether the unit is providing protection for the personnel and surrounding environment and/or protection of the pathogen being worked on. Class I BSCs protect personnel and the environment but not the pathogen being worked on. Class II BSCs protect personnel, environment, and the pathogen being worked on. Class III, which is known as glove boxes, provides a physical barrier between personnel and the pathogen. For BSL-3 laboratories, Class II, type A2 and B2 BSCs are primarily used.
FIGURE 4: BSL-3 lab stacking.
Performing a BSL-3 site assessment should include preplanning the site observations, performing the site observations, interviewing laboratory and maintenance personnel, and performing HVAC system and BSC testing.
FIGURE 5: BSL-3 laboratory space pressurization.
Some of the NIH HVAC requirements for a BSL-3 lab include:
FIGURE 6: A dual tunnel air-handling unit.
The BSL-3 laboratory is located in a large, single-story building that contains general chemistry labs, office space, mechanical spaces, and electrical spaces. The lab layout consists of ante room, gowning rooms, a clean corridor, lab spaces, BSC spaces, a decontamination space, and autoclaves (see Figure 3). There is a dedicated mezzanine above the lab for accessing the ductwork, control valves, and exhaust system HEPA filter bank (see Figure 4). The lab has dedicated HVAC and exhaust systems that were located on the roof next to each other (see Figure 4). The chilled water system and heating water system were located in a dedicated mechanical room.
The lab space pressurization had the ante-room with the lowest negative space pressure with the space pressure reducing through the gowning to the clean corridor, lab spaces, and finally with the BSC spaces having the most negative space pressurization (see Figure 5).
The AHU has two tunnels with either of the tunnels able to meet the lab supply airflow, cooling, and heating requirements. The AHU has a MERV-8 pre-filter and MERV-14 final filter (see Figure 6). The exhaust system has dual-exhaust fans bypass air plenum (see Figure 7).
The space temperature readings ranged between 71º-74º, and the relative humidity (RH) ranged between 47%-53%.
The HVAC control philosophy has the AHU and exhaust fan on the building management system (BMS) while the supply air and exhaust air venturi valves were on a separate control system. The basic supply air control philosophy was to maintain 2 inches of water gauge (INWG) supply duct pressure during occupied modes and 1 INWG during unoccupied modes. The supply air and return air venturi valves are designed to modulate to a lower airflow set point during unoccupied mode.
FIGURE 7: Laboratory exhaust fans with a bypass plenum.
The BSL-3 lab evaluation found many things that were good, bad, and ugly. The good are items that meet the industry standard of care, the bad are those that have the potential to cause substantial contamination, and the ugly are items that have a high probability of causing unwanted contamination.
The Good
The Bad
The Ugly
Based upon the site observations, testing, and analysis, the following changes are recommended:
The lab owner had the foresight to have the laboratory assessed after 10 years of operation. Though the laboratory had no prior contamination issues and the HVAC system operated adequately enough to provide reasonable environmental conditions, the HVAC and exhaust systems needed substantial repairs and renovations to meet the original system design intent and ensure reliable future operation.
[ljubaphoto]/[E+] via Getty Images