I remember we installed natural gas tanks for our pick up trucks. There were all sorts of tests done like dropping them off a crane suspending them 100 feet and dropping them. Couldn't get them to explode. When ignition was added they just did a flash fire then out it went out. No percussion per se.I guess that's why bombers don't use propane or natural gas in their terrorist arsenal.There are certainly a risk on the back end but where aren't they at risk.. If you get hit that hard in the back the driver will be 30 feet in front and more likely to suffer back lash.