15.8.2 Air exhausted from the recovery system of a powder operation shall not be recirculated unless the concentration of particulate matter in the exhaust air has been reduced to a level that is considered safe for personnel occupational exposure and suitable equipment continuously monitors the filtration system to signal the operator and to automatically shut down the operation in the event the filtration system fails to maintain the air in this condition. 15.8.3* Enclosures. Enclosures either shall be listed for the specific application or shall be designed to resist the destructive effects of an internal deflagration. Any enclosure that is not so listed and is effectively tight, such as a spray booth, dust collector, powder recovery device, or other enclosure, shall be provided with one of the following: (1) Deflagration venting (2) A deflagration suppression system that meets the requirements of NFPA 69, Standard on Explosion Prevention Systems 15.8.4 Ventilation for fluidized beds and electrostatic fluidized beds shall be designed to effectively prevent escape of nondeposited powder from the enclosure. 15.8.5 The ventilation system shall confine air-suspended powder to the booth and the recovery system at all times.
15.9 Drying, Curing, and Fusing Equipment.
15.9.1 The temperature of the object or material being coated shall be maintained at least 28°C (50°F) below the autoignition temperature of the powder. 15.9.2 Drying, curing, and fusing equipment shall meet all applicable requirements of NFPA 86, Standard for Ovens and Furnaces.
15.10 Operation and Maintenance.
15.10.1 The area surrounding the spray area, including horizontal surfaces such as ledges, beams, pipes, hoods, and booth floors, shall be maintained to prevent the accumulation of powder. 15.10.2 Surfaces shall be cleaned in a manner that does not scatter powder or create dust clouds. Vacuum sweeping equipment, where used, shall be of a type approved for use in hazardous locations. 15.10.3 Means shall be provided to prevent tramp metal or spark-producing material from being introduced into the powders being applied. 15.10.4 Signs stating NO SMOKING OR OPEN FLAMES in large letters on contrasting color background shall be conspicuously posted at all powder coating areas and powder storage rooms. 15.11 Automated Electrostatic Powder Spraying Equipment. The provisions of Chapter 11 and other sections of Chapter 15 shall apply to fixed electrostatic equipment, except that electrical equipment not covered therein shall comply with Section 15.7. 15.12 Handheld Electrostatic Powder Spraying Equipment. The provisions of Chapter 12 and other sections of Chapter 15 shall apply to electrostatic hand guns where used in powder coating, except that the high-voltage circuits shall be designed so as not to produce a spark capable of igniting any powder–air mixtures likely to be encountered instead of the vapor–air mixtures referred to and except that electrical equipment not covered therein shall comply with Section 15.7.
15.13 Electrostatic Fluidized Beds.
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