One means of controlling ignition sources in Hazardous Locations (HAZLOC) is to “pressurize” the enclosure/cabinet. This is not usually a primary means of protection but is a fallback when a facility realizes that an electrical enclosure/cabinet is sitting in their newly recognized Class 1, Div 2 HAZLOC. So I get a panic e-mail about this newfound issue and the screams of how much it will cost to move this non-rated cabinet.
My answer is always, does the cabinet have a NEMA rating that would allow it to be “pressurized”?
If so, can we assess the cabinet and establish the “Type” of pressurizing we can use to provide protection so that this cabinet does not become an ignition source?
When this means of protection is used in the workplace, the cabinets MUST be labeled to bring notice to this protection means and the hazards that some of these protection schemes pose to workers; yep, the elimination of an explosion hazard can come with a trade-off by using an inert gas (e.g., an asphyxiant). But when we use “Type Z” pressurization, we have to have the means to notify personnel in the area (or a constantly attended location) that the cabinet is no longer pressurized; this would be either a visual or audible alarm (or, as we do it – BOTH audible and visual). But these alarms cost $, so NFPA offers an “exception” to the alarms by way of CONTROLLING the gas valve that is providing the gas that “pressurizes the cabinet.” And yes, you guessed it, that valve(s) MUST be: