Overview Environmental requirements of datacom equipment vary depending on the type of equipment and/or manufacturer. However@ a consortium of server manufacturers has agreed on a set of four standardized conditions (Classes 1 to 4)@ listed in Thermal Guidelines for Data Processing Environments (ASHRAE 2008). A fifth classification@ the Network Equipment??Building Systems (NEBS) class@ is typically used in telecommunications. ? Class 1: typically a datacom facility with tightly controlled environmental parameters (dew point@ temperature@ and relative humidity) and mission-critical operations; types of products typically designed for these environments are enterprise servers and storage products. ? Class 2: typically a datacom space or office or lab environment with some control of environmental parameters (dew point@ temperature@ and relative humidity); types of products typically designed for this environment are small servers@ storage products@ personal computers@ and workstations. ? Class 3: typically an office@ home@ or transportable environment with little control of environmental parameters (temperature only); types of products typically designed for this environment are personal computers@ workstations@ laptops@ and printers. ? Class 4: typically a point-of-sale or light industrial or factory environment with weather protection@ sufficient winter heating@ and ventilation; types of products typically designed for this environment are point-of-sale equipment@ industrial controllers@ or computers and handheld electronics such as PDAs. ? NEBS: per Telcordia (2001@ 2006)@ and typically a telecommunications central office with some control of environmental parameters (dew point@ temperature and relative humidity); types of products typically designed for this environment are switches@ transport equipment@ and routers. Because Class 3 and 4 environments are not designed primarily for datacom equipment@ they are not covered further in this chapter; refer to ASHRAE's (2008) Thermal Guidelines for Data Center Environments for further information.