If smoke is coming out of your engine, will your car explode?

[EmilyJackie]

Sorry, i have no knowledge about cars but today on the turnpike I saw an accident. The people weren't hurt or anything but one of the car's engine got really messed up. Then smoke started coming out! I wanted to warn them to get out because the car might explode but my sister told me that wouldn't happen. I just want to know is my sister right or were those people really in danger?