Serious rust can compromise the strength of structural joints. Serious rust can also allow unwanted exhaust fumes enter the cabin area.
Harmful
its harmful because when metal goes rusty it looses it power and then eventually the car will fall apart.
Corrosion.
That depends on what effect is desired; If you like to breathe, it is a useful gas; If you prefer that your car (or whatever) not be rusty (oxidized), then it is a harmful gas.
harmful
Steel or iron goes rusty in water.
Rusty Beaman goes by Rusty.
Rusty Goes to London was written by Ruskin Bond
copper copper
Rusty Wallace goes by Rubberhead.
The car is safe due to the strength of the body. If it is rusty the strength goes away quickly. Also all the brake and steering parts are mounted to pieces that rust also.
Rusty Greer goes by The Red Baron.