Q. How far does the electrical area classification extend beyond the open face of my spray booth?
A. For open face spray booths, the Class I, Division 2 area extends 3 feet from the opening of the spray booth. No longer is there a difference when the ventilation system is interlocked with the spray application equipment.
Chapter 6 of NFPA 33 has been extensively revised for the 2011 Edition. Changes include revisions of the figures illustrating the area classifications in and around spray areas, spray booths, spray rooms and equipment.
From the 2011 Edition of NFPA 33, Standard for Spray Application Using Flammable or Combustible Materials:
6.5.2 – If spray application operations are conducted within a closed-top, open-face or open-front booth or room, as shown in Figure 6.5.2, any electrical wiring or utilization equipment located outside the booth or room but within 915mm (3 ft) of any opening shall be suitable for Class I, Division 2; Class I, Zone 2; Class II, Division 2; or Zone 22 locations, whichever is applicable.
Figure 6.5.2 from NFPA 33, Standard for Spray Application Using Flammable or Combustible Materials 2011 Edition
The 2011 Edition of NFPA 70, National Electric Code (NEC) still has the old 5 feet if the exhaust ventilation system is interlocked with the spray application equipment and 10 feet if it is not interlocked.
However there has been an extensive effort put forth by the committees responsible for both documents to bring them together with regard to electrical area classifications. The 2014 Edition of the NEC will include extracted text and figures from the 2011 Edition of NFPA 33 and both documents will be in agreement.