We may not like the surface durability of sheet rock, but it has great fire resistance . If you use in obs or plywood on the walls of a home shop especially if attached to a home put sheet rock under it for the fire resistance. The life you may save could be yours or your family's. Older mobile home are a good example of what fire can do if the walls are ply wood only. In the fire service we call them 10 second fires. Which means a person has about 10 seconds two leave and live in case of a fire. This was drove home to me after a mobile home fire where the only thing standing was the hot water heater surrounded by the only sheet rock in the home. As a side note modern noble home do have sheet rock. With the grinding ,welding,and hot work we do in our shops ,stay safe out there.