In terms of safety, we have already seen a number of videos from various CNG suppliers that show CNG tanks on buses that have been shot, that have been set fire to, that have been driven into walls, and there is zero explosion with these things. In terms of safety, CNG in many ways is probably safer than diesel. CNG has a very specific ignition point. It has to have a mix with air of about 5% to 15% for it to ignite. Anything outside those realms, it doesn't do anything. It just disperses into the atmosphere, unlike diesel. If you get a leak in a diesel tank, all the diesel spills onto the floor and mixes within the environment. As for CNG, if it leaks from the tank, it evaporates.
On May 1st, 2012. See this statement in context.