The pressure is higher in A/C and heat pumps, and you have liquid propane in half of the system. A leak there will quickly create a huge volume of flammable propane-air-mixture at room pressure. The usual plumbing for heating and cooking is at a very low (over-)pressure, 100mbar or something, and your distribution network in town is typically at 1bar. A leak there is less bad and will take some time to fill up space with enough flammable propane-air-mixture to be dangerous, enough time to maybe sound an alarm and evacuate. Generally, a basement full will obliterate the occasional building in any case.
I would think that with a closed loop system the risk of a serious problem would be quite low.