Relative Humidity 21 : The ratio between the amount of water vapor in the gas at the time of measurement and the amount of water vapor that could be in the gas when condensation begins, at a given temperature
NFPA 79 Electrical Standard for Industrial Machinery, 2002 ed. http://www.nfpa.org/assets/files/AboutTheCodes/79/ 79-A2002-rop.pdf, (Electr Std for Ind Machinery - Amer) {225 NFC}