Propane is heavier than air. A leak sinks into the bilge and waits for a spark. A-1 is the standard that keeps the gas outside the boat until it reaches the appliance, and gives it a way overboard if it leaks.
What it covers
ABYC lists A-1 as Liquefied Petroleum Gas (LPG) Systems. In our words: the cylinder and where it lives, the locker and its drain, the regulator, valves and shut-offs, the supply line, and the appliances.
What surveyors check against it
Cylinder and locker. As quoted by Soundings and on owner forums, cylinders are secured, accessible, and outside the boat or in a dedicated locker that's vapour tight to the hull interior, above the waterline and opens from the top. Lockers shouldn't invite gear storage. See LPG locker drain.
Drain. From the locker's lowest point overboard, to an outlet lower than the locker floor and above the waterline, with no dips. Soundings reports ABYC recommends vents at least 20 inches from any hull opening.
Shut-off and detection. Practical Sailor's safe installation built to A-1 has a pressure gauge to leak test the system, a solenoid at the cylinder, a regulator and a sniffer at a low point. See no gas detector.
Small cylinders. Soundings quotes ABYC A-30: cylinders over 8 ounces stored outside the boat.
Citing it in a finding
"Reroute the gas locker drain to fall continuously overboard to an outlet above the waterline, ABYC A-1." For a leak, the finding says close the cylinder and don't use the system, before any standard is named.