Without question, the #1 question we receive regarding Hazardous Locations is… When do I need one? With flammable liquids (e.g., FP<100F) it is easy to perform the evaluation. But what if my flammable solution is a CAT 3 or 4 (i.e., Class IIIA or IIIB)?
As the title says, not all flammable solutions require us to establish a HAZLOC. And a CAT 3 or 4 flammable liquid is the perfect scenario to discuss…
Using my favorite RAGAGEP for establishing a HAZLOC (NFPA 497), they make it very clear that a “combustible liquid,” or as we call them today, a CAT 3 or 4 flammable liquid, may not need an area to be a HAZLOC.
A combustible liquid will form an ignitible mixture only when heated above its flash point. The degree of hazard with Class II liquids is lower because the vapor release rate is low at normal handling and storage temperatures. These liquids will generally not form ignitible mixtures with air at ambient temperatures unless heated above their flash points. Also, the vapors will not travel as far because they tend to condense as they are cooled by ambient air.
Class II liquids (FP>100°F <140°F) should be considered capable of producing an ignitible mixture near the release point when handled, processed, or stored under conditions where the liquid could exceed its flash point.
Class IIIA (FP>140°F <200°F) liquids do not form ignitible mixtures with air at ambient temperatures UNLESS HEATED above their flash points. Furthermore, the vapors cool rapidly in the air and condense. Hence, the extent of the area requiring electrical classification will be small or nonexistent.
Class IIIB (FP>200°F) liquids seldom evolve enough vapors to form ignitible mixtures even when heated, and they are seldom ignited by properly installed and maintained general-purpose electrical equipment. A Class IIIB liquid will cool below its flash point very quickly when released. Therefore, area classification is seldom needed and Class IIIB liquids.