hope the comprehensive answer of Eric Hahn clarifies your apprehensions. In context of india, pl note that even the dark colored LPG cylinders (of HPCL) kept in hot summer sun can reach even 70 deg C. The SVP of 80:20 mix of C3:C4 at 70 deg C is much lower than the bursting test pressure (of 90 bar at the manufacturing). Therefore there is no probability of exposure of direct sun causing explosions of LPG cylinders. The frequent explosions of LPG cylinders are reported in India as these are almost always kept inside the kitchen and other indoor places. when these cylinders get exposed to any indoor fire, these get heated to much higher temperatures and the internal pressure rises above the bursting pressure. That results in catastrophic explosion with violent force and sudden release of a lot of inflammable gas into the already raging fire.
have been campaigning against this DANGEROUS practice of keeping LPG cylinders indoors in India for a long time with all Govt authorities, but without any Success so far.