Let’s remember what’s needed to start a fire: oxygen, heat and fuel. Otherwise known as the fire triangle, Ally from Ally Safety shows us three ways to prevent a fire from spreading. The three ways of preventing fire involve eliminating any part of the fire triangle. When we talk about hazardous locations we are talking about buildings or facilities that have an increased risk of causing fires due to normal operating conditions. In hazardous locations, the fire triangle is present consistently. As electricians, we need to classify and install equipment in these areas that reduce the risk of fire and explosion. For example, eliminating a spark in an industrial plant can be done with ppe (Beakert Technology gives us a simple demonstration) and/or special electric equipment rated for such a case.
Combustible, ignitable, flammable all mean pretty much the same thing: Able to start fires easily. So when we are working in these hazardous locations, certain requirements like explosion-proof boxes, low-heat lights, etc are required in code to prevent and eliminate as much as possible the ability to cause fire!! We don’t want to hear Eddie Murphy’s uncle screaming “Now that’s a fire!“
It starts with the elimination of heat and sparks in the hazardous location. So, in the United States, we refer to Hazardous locations as Class I, II, and III and then Division I or Division II. The International community uses Zones instead of Classes and Divisions. Below is a quick table that summarizes the classifications.
In a nutshell, Combustible materials are at the heart of these hazardous locations: Combustible liquids (Class I), Combustible dust (Class II) and Combustible fibers (Class III). The two divisions simple are whether the presence of combustible materials are present in normal operating conditions (Division I) or are only present due to abnormal conditions (Division II).
Chapter 5 of the NEC begins with Article 500 describing the Classes and Divisions. Articles 501, 502, and 503 then proceed to give further safety guidance based on the Classes. Then we have an article entitled Intrinsically Safe Systems. NEC 2017 defines an intrinsically safe circuit [as applied to Hazardous (Classified) Locations] as “a circuit in which any spark or thermal effect is incapable of causing ignition of a mixture of flammable or combustible material in air under test conditions.”
Article 505 speaks about Zone 0,1, and 2 locations. These are like Class I (Article 501) combustible liquids, flammable gas and vapors. Article 506 Zones 20, 21, and 22 encompass Class II and Class III (articles 502 and 503 respectively) by including combustible dusts and ignitable fibers.