## 1 Introduction  
The indoor environmental conditions in an operating room (OR) are usually designed to satisfy the patients' comfort and health [1]. The International Standard ISO 7730 [2], which deals with the specification of the conditions for thermal comfort, does not make a difference between types of indoor spaces in terms of thermal comfort. Therefore, any OR has to meet the requirements of this standard, similar to office premises or a theatre hall. The thermophysiological comfort of people in the indoor environment depends on three groups of factors [3]:  
* Environmental factors: air temperature, mean radiant temperature, relative air humidity, air movement (air velocity);
* Factors related to the state of the human body: thermoregulation mechanism, central nervous system, cardiovascular system, respiratory system, skeletal-muscular system, digestive system;
* Factors related to clothing/textiles as a barrier between the body and the environment: insulating ability (resistance to heat transfer), air permeability, water vapour permeability, water repellency, drying rate. The patient in the OR stays together with the medical staff, which involves different actors: surgeons, anaestists, nurses, assistants. The thermophysiological comfort of everyone has to be satisfied in order to assure their high-quality performance during the operation (for the staff) or their health (for the patient). Though the staff and the patient occupy the same indoor environment, all three groups of factors that define their thermophysiological comfort differ. The most significant difference between the staff and the patient is the clothing: the patient is usually necked and covered with a surgical drape, while the medical staff wears protective clothing. The original function of surgical clothing was to protect the patient in the OR from a possible impact of the surgical team. Later on, having the results from the studies on the dangers associated with blood-borne pathogens, the role of the surgical clothing changed: the need to protect the surgeons from the patient was added to the need to protect the surgeons from the patient himself [3]. Furthermore, the clothing of the surgeons and the surgical nurses differs from the clothing of the anaestists and the technicians who may handle specific medical equipment in the OR. The factors related to the state of the human body are also different. The patient is lying down under anaesthesia, his/her thermoregulatory mechanism is inhibited with increased risk for perioperative hypothermia, the body is under stress and internal organs and body tissues are exposed to the environment with possible blood losses. At the same time, behavioural responses to thermal discomfort are impossible. Meanwhile, the medical staff are standing; the surgeons work stationarily around the operating table, while the nurses and the anesthesiologist can move slightly. The mental load and physical stress for the staff are also different, being most heavy for the surgeons [4; 5]. The environmental factors in the OR also differ: it was found that in the area just below the operating lamps, due to the radiation heat, the air temperature is higher on average by 3 \({}^{\circ}\)C than the rest of the OR [6]. Obviously, there is a conflict in the requirements for the thermal environment in the OR. Even though the heating, ventilation and air-conditioning system in the OR provides standard comfort conditions (20-22 \({}^{\circ}\)C, 65% relative humidity) [2], it is likely that only nurses and anaestists will be able to determine the thermal environment as comfortable. In cases where there is no individual system or device (blanket) for warming the patient, the air temperature in the OR should not be below 23 \({}^{\circ}\)C [4] or even higher than 24 \({}^{\circ}\)C [7]. At the same time, the air temperature for the surgeons in heavy protective gowns during extended operations is suggested to be lower than 18 \({}^{\circ}\)C [7]. The technical standards for the indoor environmental in an OR were summarized in [5].