NFPA 91-1999 Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids.
5-1 Electrical Equipment. All electrical equipment and instal- lations shall comply with the requirements of NFPA 70, National Electrical Code ® . 5-2* Static Electricity. 5-2.1* All system components shall be conductive. Bonding and grounding with a resistance of less than 1.0 × 10 6 ohms to ground shall be provided. Exception: Nonconductive equipment shall be permitted to be used as covered in this document by Chapter 3, Corrosive Materials, where it is shown that the material conveyed does not create an atmosphere that is above 25 percent of the lower flammable limit (LFL). 5-2.2 Where belt drives are used, the belts shall be electrically conductive at 1 megohm or less. 5-3 Manifolds. Operations generating flames, sparks, or hot material such as from grinding wheels and welding shall not be manifolded into any exhaust system that handles flamma- ble or combustible materials. 5-4 Open Flames and Sparks. The requirements of 5-4.1 through 5-4.3 shall be applied retroactively. 5-4.1 Cutting and welding shall comply with the applicable requirements of NFPA 51B, Standard for Fire Prevention During Welding, Cutting, and Other Hot Work.
5-4.2 Grinding, chipping, and other operations that produce either sparks or open flame ignition sources shall be con- trolled by a hot work permit system in accordance with NFPA 51B, Standard for Fire Prevention During Welding, Cutting, and Other Hot Work. 5-4.3 Smoking shall be permitted only in designated areas. 5-5 Removal of Ferrous Materials. Ferrous materials capable of igniting combustible material being conveyed shall be removed from the exhaust stream by magnetic separators of the permanent or electromagnetic type. Where electromag- netic separators are used, provisions shall be made to indicate the loss of power to the electromagnetic separators. 5-6* Belt Drives. Belt drives shall be designed to stall without the belt slipping, or a safety device shall be provided to shut down the equipment if slippage occurs. 5-7* Bearings. Roller or ball bearings shall be used on all processing and transfer equipment. Lubrication shall be per- formed in accordance with the manufacturer’s recommen- dations. Exception: Bushings shall be permitted to be used when an engineer- ing evaluation shows that mechanical loads and speeds preclude igni- tion due to frictional heating. 5-8 Equipment. Equipment with moving parts shall be installed and maintained so that true alignment is maintained and clearance is provided to minimize friction.
NFPA 91 pdf download.