1.   Then a small spark of comfort occurred to him.

2.   But they have been unable to show how such a spark could have occurred.

3.   But they have yet to prove that such a spark could have occurred.

4.   That way, if a spark occurs, it will be far enough away from the dead battery to prevent explosion.

5.   The board also recommended airplane design changes such as fuel temperature monitors and the use of inert gases in tanks to prevent explosions should a spark occur.