Heating Combustible Liquids and Electrical Classification(s)

This week we saw OSHA issue a $1.5M citation after an explosion killed four workers at a silicon chemical products manufacturer.  All of the citations were classified as Willful and all were related to using equipment that was not approved for a hazardous location (HAZLOC).  This week I was working with a client doing a PHA that involved heating the batch(s), which contained Class IIIB combustibles, to temperatures well above their flashpoints and we were had to do a HAZLOC assessment for the process building. The first thing we have to recognize is that NFPA 497 still uses “Flammable Classes” and OSHA now uses Flammable Categories. 

So let’s first look at the definitions:

OSHA

1910.106(a)(19) Flammable liquid means any liquid having a flashpoint at or below 199.4 °F (93 °C). Flammable liquids are divided into four categories as follows:

…

1910.106(a)(19)(iv)Category 4 shall include liquids having flashpoints above 140 °F (60 °C) and at or below 199.4 °F (93 °C). When a Category 4 flammable liquid is heated for use to within 30 °F (16.7 °C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 3 liquid with a flashpoint at or above 100 °F (37.8 °C).

NFPA

Combustible Liquid. Any liquid that has a closed-cup flash point at or above 100°F (37.8 °C), as determined by the test procedures and apparatus set forth in NFPA 30.

Combustible liquids are classified in accordance with the following:

Class II Liquid -Any liquid that has a flash point at or above 100°F (37.8°C) and below l 40°F (60 °C);

Class III Liquid – Any liquid that has a flash point at or above 140°F (60 °C);

Class IIIA Liquid – Any liquid that has a flash point at or above 140°F (60°C), but below 200 °F (93 °C);

Class IIIB Liquid – Any liquid that has a flash point at or above 200°F (93°C).

In this situation, we were dealing with Class IIB Combustible liquids or as OSHA calls them – Category 4 flammable liquids.  So here is how it worked out…

1910.106(a)(19)(iii) Category 3 shall include liquids having flashpoints at or above 73.4 °F (23 °C) and at or below 140 °F (60 °C). When a Category 3 liquid with a flashpoint at or above 100 °F (37.8 °C) is heated for use to within 30 °F (16.7 °C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 3 liquid with a flashpoint below 100 °F (37.8 °C).

1910.106(a)(19)(iv) Category 4 shall include liquids having flashpoints above 140 °F (60 °C) and at or below 199.4 °F (93 °C). When a Category 4 flammable liquid is heated for use to within 30 °F (16.7 °C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 3 liquid with a flashpoint at or above 100 °F (37.8 °C).

1910.106(a)(19)(v) When liquid with a flashpoint greater than 199.4 °F (93 °C) is heated for use to within 30 °F (16.7 °C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 4 flammable liquid.

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.

Bottom line, when we have Category 4 flammable liquid (e.g. Class IIIB Combustible Liquid) area electrical classification is not necessary/required even when we are heating these materials within 30° of their flashpoints or even above their flash points.