Many years ago I had a 100lb bottle feeding my house. One summer day I got home after work when they had filled the bottle in the morning. Just as I pulled in the driveway and parked next to the bottle it was like someone pulled the handle on a CO2 fire extinguisher. A cloud of white vapor and a cone of gas coming from the top of the bottle. Only lasted about 5 seconds but long enough for me to call the propane dealer. Fortunately the person that answered new the business and after my description he just said "Popping off is she." He then explained the over pressure valve and how filling the tank in the morning at 60* the gas expanded by the time I got home to 90* with the bottle sitting in the sun. He offered to send someone out but after his description I just told him I'd keep an eye on it and call back if it continues.
