Self-contained breathing apparatus pressure changes with ambient temperature. As temperature decreases, the pressure inside the cylinder decreases. The relationship between the temperature and the pressure of a gas is defined by the formula "PV" = "nRT". (See Universal gas constant.) What is particularly important to understand from the formula is that the temperature is in kelvins, not degrees Fahrenheit. Consider the freezing point of water at 32 °F (0 °C, 273.15 K) and compare it to 96 °F (35.6 °C or 308.71 K; normal human body temperature is 37 °C). While 96 is arithmetically three times 32, the difference in temperature from a
Human body temperature to temperatures of peripheral tissues. Core temperature is normally maintained within a narrow range so that essential enzymatic reactions can occur. Significant core temperature elevation (hyperthermia) or depression (hypothermia) that is prolonged for more than a brief period of time is incompatible with human life. Temperature examination in the rectum is the traditional gold standard measurement used to estimate core temperature (oral temperature is affected by hot or cold drinks and mouth-breathing). Rectal temperature is expected to be approximately one Fahrenheit degree higher than an oral temperature taken on the same person at the same time. Ear thermometers measure eardrum