(a) Fired prsssure vessels, internal combustion engines, electric motors except those of the nonsparking or wholly enclosed type, or those operating storage battery trucks, shall not be operated within 25 feet of any booth, room booth, or other space in active use for spraying operations, except under the following conditions:

1. (1) When nonflammable materials are used.
2. (2) When the apparatus is separated from the spraying area by a wall or partition. All doors and windows in such walls or partitions shall be kept closed at all times except for the passage of persons or vehicles.