Guide for the Care and Use of Laboratory Animals - Office of ...

140 GUIdE FOR ThE CARE ANd USE OF LAbORATORy ANIMALSTemperature is best regulated by having thermostatic control for eachholding space. Use of zonal control for multiple spaces can result in temperaturevariations between spaces in the zone because of differences inanimal densities and heat gain or loss in ventilation ducts and other surfaceswithin the zone. Individual space control is generally accomplished by providingeach space with a dedicated reheat coil. Valves controlling reheatcoils should fail in the closed position; steam coils should be avoided orequipped with a high-temperature cut-off system to prevent space overheatingand animal loss with valve failure.Humidification is typically controlled and supplemented on a system orzone basis. Control of humidification in individual holding spaces may bedesirable for selected species with reduced tolerance for low relative (e.g.,nonhuman primates) or high humidity (e.g., rabbits).Most HVAC systems are designed for average high and low temperaturesand humidities experienced in a geographic area within ±5% variation(ASHRAE 2009). Moderate fluctuations in temperature and relative humidityoutside suggested ranges are generally well tolerated by most species commonlyused in research as long as they are brief and infrequent; holdingspaces should be designed to minimize drafts and temperature gradients.Consideration should be given to measures that minimize fluctuations intemperature and relative humidity outside the recommended ranges due toextremes in the external ambient environment. Such measures can includepartial redundancy, partial air recirculation, altered ventilation rates, or theuse of auxiliary equipment. In the event of an HVAC system or componentfailure, systems should at the minimum supply facility needs at a reducedlevel, address the adverse effects of loss of temperature control, and, wherenecessary, maintain critical pressurization gradients. It is essential that lifethreateningheat accumulation or loss be prevented during mechanicalfailure. Temporary needs for ventilation of sheltered or outdoor facilities canusually be met with auxiliary equipment.Air handling system intake locations should avoid entrainment of fumesfrom vehicles, equipment, and system exhaust. While 100% outside air istypically provided, when recirculated air is used its quality and quantityshould be in accord with recommendations in Chapter 3. The type andefficiency of supply and exhaust air treatment should be matched to thequantity and types of contaminants and to the risks they pose. Supply air isusually filtered with 85–95% dust spot efficient filters (ASHRAE 2008). Incertain instances, higher efficiency filters (e.g., HEPA) may be beneficial forrecirculated supply air and air supplied to or exhausted from specializedareas such as surgical and containment facilities (Kowalski et al. 2002).