5.7 pressures. Between 530 and 2930 N/m 2 (4-22 mmHg) carbon dioxide brings on adaptive biochemical changes. Above 2930 N/m 2 , pathological changes begin. Higher partial pressures cause unconsciousness and death (5.1). Thus, the partial pressure of oxygen, the partial pressure of carbon dioxide, and the constancy of pressure of the breathing mixture are critical factors for the well-being of human beings. Deviations in those parameters bring on rapid debilitation and possible death. V.2.3: Temperature and Humidity: Thermal comfort is a function of dry-bulb temperature and relative humidity. Dry-bulb temperature is that measured by a dry thermometer in air. Relative humidity is the ratio,expressed as a percentage,of the water content in the air to the water content if the air were saturated. Comfort tests have determined that, for relative humidities between 30% and 70%, most 9eople prefer a temperature 295°K (71°F). Other comfort tests have set a comfort zone of 296-298°K (73-77°F) for 25%-60% relative humidity (5.2). Combining the two results, an acceptable comfort zone is 295-298°K (71-77°F) and 30%-60% relative humidity . Storage of animal protein in the food cycle requires lower temperatures. Refrigerators run at 277°K (40°F) and freezers run at 255°K (0°F). Constancy of temperature is critical to human life. Below 273°K,water freezes and so do humans. Above 311°K (l00°F), human performance is sharply curtailed and unconsciousness may occur. These effects are not immediate, however, unless the environment strays far beyond the extremes described above. The effects of variation of humidity are neither serious nor immediate on human beings. V.2.4: Food: Table 5.2 lists the recommended dietary allowances for adult men and women in the United States of America. Where the values for men and women differ, the higher value appears in the table. Also, the values shown are for the 18-35 years of age
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