According to the national standards publication NFPA58, a propane tank with 20 pounds (5 Gal) of gas at 70°F would have a pressure of 145 psi; at 90°F, pressure would increase to 180 psi; at 105°F, pressure continues to rise to 235 psi, and at 130°F, pressures of 315 psi would be reached.
Why is this important to know? Excessive pressures can cause the tank's safety relief valve to discharge.
What conditions contribute to excessive temperatures? Answer: Direct sun, dark paint colors, external heat sources, etc.