The American National Standard for storage and use of propane cylinders is NFPA 58-2004, Liquified Petrleum Gas Code, which is adopted in all 50 states. NFPA 58 does not allow 20# propane cylinders to be used or stored in residences. This includes garages attached to residences, and detached garages. Use is permitted to a limited degree in industrial buildings, but only where it would be impractical to locate the cylinder outdoors and pipe the gas in.
The major hazard is not BLEVE, but overheating and release of the propane torch fire, which can extend 20 ft from a cylinder (from the pressure release valve). This can spread fire horizontally, and can be a significant threat to firefighters.
ALWAYS keep your propane tanks outside at all times.