The purpose of this paper is to present a thermal model of the human body which is applicableto environmental enclosures that are characterized by high occupant densities and relativelylow mechanically induced ventilation rates. The model will predict time-temperature historiesof the deep body tissues and the skin surface of a sedentary occupant. The environmental caseof particular interest for this study is one which simulates the situation in which a largegroup of people is trapped in a high-rise building, survival shelter, or similar enclosure,while being subjected to a radiant heat load from a fire adjacent to the shelter space. Severalshelter environments will be examined in terms of air circulation rates, initial equilibriumconditions; radiant input rates, and occupant density to determine their effect on the shelteree'sthermal response.