To start the new year off on the right foot, I’ve cleaned my closets, matched all of my family’s socks, (almost) emptied my inbox, and made a list of the tough topics that need to be addressed on iDigHardware and/or in a Decoded article.  Earlier this week I shared my article on SCIF doors, which was one of those subjects that I really needed to take some time to understand and explain.  It’s much easier when I can just write down something that I already know, but eventually I will have shared everything that’s already in my head.  So it’s time to tackle the tough questions.

I have been asked about electrified hardware for hazardous locations many times.  These requests often come through when access control is needed for a door serving a Class II, Division 1 area, for example.  Classes I, II, and III are covered in NFPA 70 – National Electrical Code, in Chapter 5 – Special Occupancies.  The original sources of this information are the NFPA standards related to the classification of flammable liquids, gases, vapors, and dusts – NFPA 497 and NFPA 499.

Chapter 5 goes into great detail regarding the classifications of these hazardous locations, based on the flammable gas, vapor, dust, or fiber that could be present, and the typical concentration of those materials.

  • Class I – Flammable gases or vapors may be present.
  • Class II – Combustible dust may be present.
  • Class III – Easily ignitable fibers or flyings may be present.

Each class has two divisions:

  • Division 1 – These hazards exist in ignitable concentrations under normal operating conditions and/or during frequent maintenance or repair work or equipment failure.
  • Division 2 – These hazards exit in ignitable concentrations under abnormal operating conditions.

The connection I’m having a hard time making is between these classifications and the requirements for access control devices used on the doors leading to (or within) those areas.  I will have some information from UL shortly and hopefully that will help to clarify this, but in the meantime I’m looking for someone with expertise on these applications.  I know that in some cases, pneumatic devices like the Von Duprin pneumatic latch retraction device (PN) are used, but I’d like to have a better understanding of the requirements.

Are you an electrical expert??  I’d love some help with this!

Note: There is a lot of good information about the NEC requirements in this booklet from Stahl, this one from Allen-Bradley, or this page from Grainger.


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