We see this often, handling, storing, and processing a Class IIIA flammable liquid, and about half will classify the area, and the other half do not. So who is right? Here is my take on the matter as I work thru the risk analysis…
In our Risk Analysis discussions, the reason WHY we can discuss reducing our HAZLOCs in the tanfarm is based on the fact that our Class IIIA Flammable liquid. It is 4 degrees away from being a Class IIIB flammable, which OSHA/NFPA does not even regulate.
NMP’s FP is 196°F (91°C). Using the NFPA 77’s recommended safety margins for Flashpoints, we will use 185°F (80°C) in our risk analysis. (See NFPA 77, Chapter 9, section 9.2.1.2 for safety margins using flash points)
In areas where NMP is NOT heated by process conditions (vs. ambient heating from the environment), the NMP cannot reach its FP, and therefore it cannot create a vapor that reaches its Lower Explosive Limit.
But in areas where we are heating up NMP, such as the distillation columns, we have a legitimate need to designate the area around these columns as Class I, Div 2, Group D HAZLOCs. Keep in mind, in the columns we are operating UNDER A VACUUM to make the distillation process more efficient. This means the NMP boils at a MUCH LOWER temperature. MEC can provide the temperatures we are OPERATING at and we can have a serious discussion around these risks. But understand, NMP boils at 112°F (44°C) when under a full vacuum.
Spills in areas where we have NMP at temps of 155°F (68°C) or LESS, we can manage the same as if we were processing Diesel Fuel, which does NOT require HAZLOC designations. In fact, diesel fuel is FAR MORE dangerous in terms of flammable properties than is NMP.
Diesel fuel has a lower FP (145°F) and 1/3 the LEL of NMP (0.5%), and yet in areas where diesel fuel is stored/handled at atmospheric pressure and AMBIENT temperatures, there are no HAZLOC requirements.
NOTE: the 155°F (68°C) temperatures are 30 degrees less than their “safety-margined” FPs. We use this 30-degree safety margin as OSHA and NFPA use this 30-degree margin as another safety margin in dealing with flammable liquids that are being heated (1910.106(a)(19)(iii) – (v). I am using BOTH OSHA’s and NFPA’s safety margins together to make it clear we can do this if we choose to.
Here is some text from NFPA 497, our RAGAGEP for establishing HAZLOCs. Remember, NMP is a Class IIIA liquid (highlighted in red below)
NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
4.2.7 Combustible Liquids.
A combustible liquid will form an ignitible mixture only when heated above its flash point.
4.2.7.1 With Class II liquids, the degree of hazard is lower because the vapor release rate is low at normal handling and storage temperatures. In general, these liquids will 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 should be considered capable of producing an ignitible mixture near the point of release when handled, processed, or stored under conditions where the liquid could exceed its flash point.
4.2.7.2 Class IIIA liquids do not form ignitible mixtures with air at ambient temperatures unless heated above their flash points. Furthermore, the vapors cool rapidly in air and condense. Hence, the extent of the area requiring electrical classification will be very small or nonexistent.
4.2.7.3 Class IIIB 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 are not included in Table 4.4.2.