Notes on NFPA 33

Recently a client wanted to know why he had to ventilate his paint booth outdoors instead of back into the building. Off the top of my head I told him that it was a safety issue more than an environmental issue, and that the concentration of flammable vapors should not exceed 25% of the Lower Flammability Limit (LFL). This answer was only partially correct. Recently I viewed NFPA 33 (Spray Application Using Flammable or Combustible Materials 2007 ). This publication, and many others, as well as interpretations of various standards, can be purchased or viewed for free online at NFPA’s website.

I learned many things, and I will be watching for these things the next time I visit a client who has a paint booth that they need to have permitted. Here are some of the things I discovered:

  • You cannot use aluminum anywhere in the paint booth.
  • You cannot make the paintbooth out of sheet metal less than 1.2 mm thick.
  • There has to be a 3 foot buffer zone around the paint booth. The only exceptions are fireproof walls and ceilings. No flammable materials can be stored less than 3 feet away.
  • You cannot move vehicles in and out of the paint booth without first stopping the painting operation.
  • The paint booth ventilation cannot be recirculated if the paint booth is to be manned.
  • If it is unmanned, air may be allowed to be recirculated, as long as certain conditions are met.
  • Vapors must not exceed 25% of the LFL.
  • Mixing rooms have to meet the same construction requirements as paint booths.
  • Mixing rooms cannot exceed 150 square feet and must have containment.
  • Air flow must be the least of either 1 cubic foot per minute per square foot or 150 cubic feet per minute in mixing rooms.
  • There are many special requirements for electrostatic coating and powder coating, such as there must be optical flame detection with a 0.5 second response time.
  • Miscellaneous spraying operations outside of a paint booth must have no spark producing equipment within 20 feet.
  • There are many other interesting requirements. If you have a painting operation, you should check out the standard.