"ABSTRACT ASHRAE TC9.9 ""Mission Critical Facilities@ Technology Spaces and Electronic Equipment"" was established to create guidance on the environmental protection of such environments in an energy conscious manner. Mission critical facilities take on many forms@ including telecommunications central offices and data centers. The former are associated with overhead cooling@ concrete slabs@ network equipment@ and DC power-plants whereas the latter are associated with raised floors@ hot aisle/cold aisles@ and AC-powered servers. The challenges associated with telecommunications and data centers are the same in many respects but different in a host of others. The decade old approaches in the telecom industry do not work in the converged ""Datacom"" environment. Many telecommunications facility operators see a number of challenges@ including introduction of high-density loads@ unknown density limits for reliable operation during normal and catastrophic cooling outages@ hot air recirculation issues as result of multiple equipment types@ and varying levels of equipment robustness. Today there is no single industry group pulling together the ideas@ resources@ and challenges of HVAC in different mission critical facilities. ASHRAE TC9.9 could play a key role in this work going forward."