Atmospheres containing an increased concentration of nitrogen and a decreased concentration of oxygen (in the range of 15%—13% v/v: normobaric hypoxia) are used more and more to reduce the risk of fire in work rooms. In Germany at present, more than 1000 persons work intermittently under hypoxic conditions. The present article aims to update an earlier review of the literature and to sum up the results of our own studies in order to estimate the health risk for the affected persons. The oxygen partial pressure and the physiological effects of normobaric (15%—13%) oxygen concentrations are similar to those encountered at an altitude of 2700—3850 m above sea level. Research in the field of physiology and mountain, altitude or aviation medicine shows that within seconds or minutes acute hypoxia results in a marked activation of the sympathetic nervous system with corresponding changes in cardio-circulatory functions. Heart rate and pulmonary arterial blood pressure increase, especially during physical activity, and the maximum level of physical performance decreases. It is still unclear whether mental functions are significantly altered at this level of hypoxia. Exposure to hypoxia for several hours can provoke symptoms of acute mountain sickness with headaches, nausea, fatigue and dizziness which may be recorded clinically by means of the standardized Lake-Louise-Score. Persons who suffer from symptomatic cardiac, circulatory or pulmonary diseases in normal air will have an even lower physical capacity under hypoxic conditions and, to prevent complications, should not be exposed to hypoxia. Meticulous technical safety precautions and a mandatory medical examination including especially the medical history and clinical signs and symptoms detect and minimize individual health risks and provide advice to exposed persons. Preliminary experimental and observational studies of people actually working under hypoxic conditions reveal a slight increase in complaints in the sense of acute mountain sickness, but not of accidents or other clinically relevant illnesses. At start of such exposures, close medical monitoring is recommended.
