This is another Wrong Chemical – Wrong Tank incident in which Anhydrous Ammonia (NH3) was off-loaded to Propane Storage Tanks.
Two 30,000-gallon propane tanks, each at 70% capacity, were additionally filled to 85% with NH3.
Similar plumbing on BOTH transport and storage tanks made the transfer possible, as both propane tanks shared common piping, had galvanized fittings, and were clearly labeled as “PROPANE”.