Comparison of indoor air quality between 2 ventilation strategies in a facility housing rhesus macaques (Macaca mulatta)

For many decades, the research community and regulatory agencies have recognized the importance of maintaining a stable and safe environment for both research animals and the personnel working with them. Studies have shown that variability in environmental quality can alter or even compromise the validity of research studies.7,12,31 For example, high levels of ammonia can radically alter the cellular composition of the trachea in rats,12 thus confounding the effects of a particular procedure or compound under investigation. In addition, inadequate indoor air quality (IAQ) can pose a significant occupational hazard to workers.16,17 The environmental quality of a particular space is defined by several indicators, including temperature, humidity, and levels of gaseous or particulate contaminants. Ventilation systems function to regulate the levels of these parameters, in addition to providing oxygen and eliminating heat.19 Moreover, ventilation removes airborne contaminants, such as odors and pathogens. Ventilation is the process of replacing the air present in a particular space with either fresh air from the outside or recirculated air that has been treated. The rate of ventilation can be measured in cubic feet per minute (cfm) of air per occupant, volume of air per floor area or, more commonly in the laboratory field, as air changes per hour (ACH), which refers to the number of times the volume of the entire space is exchanged in an hour.10,21 Although the Guide for the Care and Use of Laboratory Animals19 provides standards related to physical plant design and specifications, to date it has not provided specific recommendations regarding the environmental quality and ventilation within an animal facility, owing to a paucity of scientific evidence. Notably, the Guide’s currently recommended ventilation rate of 10 to 15 fresh ACH for an animal room was based on anecdotal evidence, empirical information, and a scientific paper that was published more than 75 y ago.7 The study published in 193825 concluded that using a recirculating air ventilation system providing at least 20% fresh air per change and 11 ACH was necessary to reduce odors to a ‘satisfactory’ level in a rudimentary animal room that housed rats and guinea pigs. The Guide acknowledges that this ventilation rate range does not reflect the effect of other factors on IAQ, which may, in practice, result in the over- or under-ventilation of a space.19 The American Society of Heating, Refrigerating and Air-Conditioning Engineers states that IAQ is represented by the thermal conditions as well as the indoor air concentrations of pollutants that are known to affect people's comfort or health in a particular space.1 The maintenance of IAQ in a space is highly dependent on effective ventilation, which is determined by several factors other than ventilation rate. Among these are the location and type of exhaust and supply vents, which will determine how well the air in the room mixes.21 In addition, the arrangement of the cages and equipment within a room can create dead zones or high-velocity drafts, which can result in the accumulation of airborne contaminants or affect an animal's ability to retain heat and moisture, respectively.18,19 Furthermore, the most recent guidelines from the American Society of Heating, Refrigerating and Air-Conditioning Engineers echo the Guide’s statement regarding the recommended ventilation rate, recognizing that a variety of factors, including husbandry protocols, bedding types, animal density, animal species, and ventilation efficiency, can render this ventilation rate range inadequate.2 However, neither document provides any guidance on how to determine whether a particular ventilation rate in a specific space is sufficient. In the end, both documents simply refer readers to the literature on ventilation of the general laboratory setting. Ventilation rate recommendations established for general laboratories are vague and broad, ranging from 4 to 15 ACH. However, in contrast to the laboratory animal field and recommendations made by the Guide, the general laboratory industry has examined the subject of ventilation in greater depth. Studies have concluded that the ACH range can be narrowed according to factors peculiar to the specific environment. One study36 performed in an unoccupied laboratory measured the rate of clearance and the airborne concentration of diethyl ether by using different ventilation rates, ranging from 4 to 16 ACH. The results demonstrated that the greatest decrease in both chemical concentration and clearance rate occurred between 6 and 8 ACH, with little benefit gained beyond 12 ACH.36 On the basis of this information, the ACH in that laboratory building was decreased from 14 to 8 ACH, thus ensuring personnel safety and saving $240,000 per year.21 In the last decade, the general laboratory community has made a pronounced shift in focus toward producing energy-efficient laboratories without compromising personnel health.6 In addition to the goal of increasing efficiency, there is interest in reducing costs, given that as much as 60% to 70% of energy costs in a laboratory building are associated with HVAC functions.21,36 In this effort to reduce costs associated with ventilation, the general laboratory industry has implemented additional strategies, including the reduction of ACH in rooms during unoccupied hours or rooms containing fume hoods. More recently, new approaches, such as demand-controlled ventilation (DCV), have been adopted.6,21,23,33 The DCV strategy is based on the concept that the ventilation rate is determined by the ‘cleanliness’ of the space. This approach requires frequent monitoring of the air quality for the levels of the specific hazardous agents expected to be present in a particular space.6,21,33 The DCV strategy allows for the maintenance of a markedly lower ventilation rate during the time when the air quality is considered ‘clean’ or sufficient, instead of maintaining a constant high airflow rate intended to satisfy the worst-case scenario. A survey of more than 300 laboratory and animal spaces that were using DCV systems revealed that the air quality within these spaces was within acceptable ranges greater than 98% of the time.32,33 This result suggests the feasibility of implementing this ventilation strategy, with considerable potential for energy savings. Despite new approaches and advances in understanding, a great need for more specific and objective guidelines to define environmental quality in animal rooms remains.7,10,20,28 Currently, ventilation rates in animal rooms of most facilities are maintained at a constant ventilation rate of as high as 20 ACH to control odors and allergens at their highest anticipated levels.33Recently, several animal facilities using DCV have maintained ventilation rates of as low as 6 ACH yet achieved adequate IAQ.33 Nevertheless, little scientific evidence is available to support a shift in the laboratory animal community toward a more individualized or evidence-based approach to the determination of optimal room ventilation. To improve IAQ and animal and personnel safety and minimize cost, we wanted to apply a DCV strategy to our new primate facility, which was equipped with a variable air volume system. To this end, we chose to reduce ACH to the minimum required to handle the heat load in the room and maintain the correct pressurization for biosecurity purposes. However, to date, the lower limits of ACH in an NHP housing room using a DCV strategy have not been reported. Therefore, the current study was aimed at determining whether we could maintain an IAQ that supports animal welfare and a safe working environment by using a DCV strategy with a base ventilation rate of less than 3 fresh ACH, when compared with a CFR ventilation system set at 12 fresh ACH. The IAQ parameters monitored were temperature, humidity, small particles (which carry allergens), volatile organic compounds (which are correlated with ammonia, considered an undesirable odor), and CO2. The facility tested housed rhesus macaques (Macaca mulatta).