Which document describes thermal environmental conditions for human occupancy?

ASHRAE 55 is the correct choice because it specifically outlines the requirements for thermal environmental conditions for human occupancy. This standard addresses factors such as temperature, humidity, airflow, and radiant temperature, which must be maintained for comfort and health in indoor environments. It provides the criteria necessary for evaluating thermal comfort and outlines methodologies for assessing both occupants' comfort levels and the necessary environmental conditions to achieve that comfort.

The other standards mentioned, while related to various aspects of building performance and safety, do not focus specifically on thermal conditions tailored to human occupancy. ISO/CEN Standards encompass a broader range of subjects, while the California Department of Public Health Standards typically pertains to health-related protocols rather than direct thermal comfort stipulations. ISO 13964, instead, deals primarily with indoor air quality and sampling procedures for airborne particles, which is outside the thermal comfort domain addressed by ASHRAE 55.