The hospital operating room (OR) thermal environmentwas investigated via field measurements that were conductedin four similar operating rooms at Denver Health MedicalCenter to determine appropriate boundary conditions forcomputational fluid dynamics (CFD) models. The primarymeasurements used infrared thermography to quantify thesurface temperatures found inside the OR. Comparisons weremade to literature to determine realistic approximations formodels of blockages and heat sources that can be used to accuratelymodel the indoor environment in CFD. Additionally, thesurface temperature of the surgical site of the patient wasmeasured to evaluate the possibility of a thermal plume fromthe surgical site. A mean surgical site temperature of 25.6°C[78.1°F] was measured, which was approximately 2.1°C[3.8°F] cooler than the surrounding skin temperature. Additionalrelevant observations of the OR environment arediscussed in order to improve the engineering knowledge ofhow these environments are used by medical personnel. Occupantheat gain was estimated at 54.3 W for an anesthetizedpatient to 102.9 W for a circulating nurse based on a combinationof field measurements and surgical personnel thermalparameters from literature. The total cooling load in a generalOR is approximately 2539 W with lighting providing 50% ofthe heat gain. The supply air T for a generic operating roomis approximately 3°C based on ASHRAE Standard 170-2008air flow requirements.