Question

what should be done if the gas cylinder at your home catches fire

Answer 1

Get out of the house immediately and then call fire brigade if it catches fire.

Answer 2

 It is really an emergency situation.

Accidentally  if your cylinder catches fire, you need to cover it with a wet blanket, and just switch off the knob of the cylinder.

You should open all the doors and windows of your room, and then you should approach any leakage or damage from the upwing and then move accordingly.

Calling the experts is the best solution.