TABLE 1 Safety Properties of Cryogenic Fluids Xenon (Xe) Krypton (Kr) Methane (CH )₄ Oxygen (O )₂ Argon (Ar) Carbon Monoxide (CO) Nitrogen (N )₂ Neon (Ne) Hydrogen (H )₂ Helium (He) Boiling Point, 1 atm F o C o -163 -108 -244 -153 -259 -161 -297 -183 -303 -186 -313 -192 -321 -196 -411 -246 -423 -253 -425 -268 Melting Point, 1 atm F o C o -169 -112 -251 -157 -296 -182 -362 -219 -309 -189 -341 -207 -346 -210 -416 -249 -435 -259 N/A Density, boiling point, 1 atm lb/cu ft 191 151 26 71 87 49 50 75 4.4 7.8 Heat of vaporization boiling point Btu/lb 41 46 219 92 70 98 85 37 193 10 Volume expansion ratio, liquid at 1 atm boiling point to gas at 60  F, 1 atm o 559 693 625 881 841 N/A 697 1447 850 754 Flammable No No Yes N/A No Yes No No Yes No