I am not sure who, where, and when this dirty little lie began, but we have been seeing an incorrect application of NFPA 70, 500.7(K) Detection System for Flammable Gases, item (3) Interior of a Building or Enclosed Space. It seems businesses are looking for any way out of having an electrically classified area and many are using this “out”; however, most of the time we find its application is woefully incorrect. First, let’s look at this option:
(K) Detection System for Flammable Gases.
A detection system for flammable gases shall be permitted as a means of protection in restricted industrial establishments.
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(3) Interior of a Building or Enclosed Space.
Any building or enclosed space that does not contain a source of flammable gases or vapors that is located in, or has an opening into, a Class I, Division 2 hazardous (classified) location and is provided with a detection system for flammable gases shall be permitted to use electrical equipment, installation methods, and wiring practices suitable for unclassified installations under all of the following conditions:
(1) An alarm (audible or visual, or both) shall be sounded at not more than 20 percent of the lower flammable limit.
(2) Sensing a gas concentration of not more than 40 percent of the lower flammable limit or a gas detector system malfunction shall activate an alarm (audible or visual, or both, as most appropriate for the area) and initiate automatic disconnection of power from all electrical devices in the area that are not suitable for Class I, Division 2.
(3) The power disconnecting device(s) shall be suitable for Class I, Division 1 if located inside the building or enclosed space. If the disconnecting device(s) is located outside the building or enclosed space, it shall be suitable for the location in which it is installed.
The allowed application is where most fail:
Any building or enclosed space that does NOT CONTAIN A SOURCE of flammable gases or vapors that is located in, or has an opening into, a Class I, Division 2 hazardous (classified) location and is provided with a detection system for flammable gases shall be permitted to use electrical equipment, installation methods, and wiring practices suitable for unclassified installations under all of the following conditions.
This option is for a building, such as a utility or storage building, located within a declared Class 1, Div 2 HAZLOC. The business has two (2) options: 1) make the building a rated building to meet Class 1, Div 2 and the appropriate Group, or 2) use this alternative option. But the building can NOT have a source of flammable gases or vapors within it! It is simply sitting in the HAZLOC. I have used this option to help clients make a change that expanded their HAZLOC and now encompasses such a building. It is costly and ineffective to relocate the utility or storage building, so I offer up this option. In a facility with a healthy respect for HAZLOCs and CONTROLLING them appropriately, this is a viable option. It is NOT a viable option for an IMMATURE HAZLOC culture.
Lastly, let’s discuss the natural gas (NG) feed to the heaters in the utility or storage building. This is understood to be exempt, as the NG used for heating is exempt from making an area a HAZLOC. So in my discussions and experience in using this alternative protection technique, the NG inside the utility or storage building is NOT an issue with applying this protection technique.