Every company must comply with the local authority having jurisdiction and follow the local codes and laws in place. For most companies, the local authority relies upon the National Fire Protection Agency (NFPA) guidelines as a source of information. According to NFPA 33 Standard For Spray Application Using Flammable or Combustible Materials, 2003 Edition, when automatic powder spray guns are used, whether liquid or powder, optical flame detection is required. Furthermore, this equipment must activate several devices within 0.5 sec of detecting the presence of a flame. This process is further described in NFPA 33, Chapter 9. However, your question is regarding manual powder coating. When manual powder coatings guns are used, optical flame detection is not required. The logic is that when the operator sees any presence of a flame, the natural instinct is to release the trigger and stop coating. By releasing the trigger, the supply of powder is stopped and the flame cannot be sustained unless a specific powder-to-air concentration exists. Powder accumulated on the booth floor and walls will not burn unless it becomes airborne in the right concentration of powder and air.
Additionally, some spray gun manufacturers sell equipment that has been approved by Factory Mutual Research (FM), an independent testing agency that puts equipment through a series of tests, to ultimately receive FM approval as a non-incendive device. This means that these powder coating guns cannot generate enough energy to produce a spark that would ignite the powder coating material. Guns with the FM approval are considered very safe to use in a powder coating environment.