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
Body piercing materials some flexibility of the material is desired. PTFE is commonly used as a retainer. Acrylic, sold as Plexiglas or any of a variety of names, is a transparent plastic, in piercing mostly used for plugs and tapers. Due to the material's smoothness, it has been used for stretching. Many overenthusiastic wearers have damaged their holes with acrylic tapers. It is not a safe material for damaged or new piercings and can not be heat sterilized by autoclave as it can melt or discolor. Acrylics can emit carcinogenic toxins above 70 degrees, which is above normal body temperature. Italso a fragile