I went on Natruell's site to do some research on CNG tank safety. 

    http://www.natruell.com/safety.html

     
Check out this video it shows engineers dropping cars (equipped with CNG tanks) from 70 feet. Next they set the tanks on pallets of wood and set the whole thing on fire. It didn't look like it got that hot. In another test, they shot the tank with a .357. It didn't do anything. Then they got an AR-15. The bullet pierced the tank but it didn't explode.  I almost forgot the sticks of TNT.

The tanks were made from aluminum and a special composite wrap.

Still accidents do happen so safety is key. Professional certified help is essential.