i ask about the design of EX- motor ; if an EX-proof motor is burnt ,can we rewound it as a ordinary motor. and i ask about the environment that we must but an EX-motor.
and if the motor will be but in an open chamber near a natural gas lines is that necessary to use EX-motor inside this chamber.

Differences between ordinary electrical motors and EX electrical motors are in aspect of mechanical protection and class of insulation due to different work conditions, so you need to care about those requirements for each electrical motor. When we are talking about differences in aspect of winding, there is no difference when you want to rewind existing EX electrical motor as you could to get new ordinary electrical motor, except you need to care about all design data of old winding of your EX electrical motor and you need to to copy them to the new winding of ordinary electrical motor.