What caused the explosion of the automobile intake branch pipe?

This question is difficult to answer, too professional. Generally, when there is gasoline in the air intake, but the throttle valve and intake valve are closed, the ignition timing is just ignited in the intake manifold at the same time, and there is no place to release it in time, which leads to explosion, which is also related to tempering. But this situation is not easy to happen. for reference only