Understanding Hazardous Location Classifications

February 25, 2014

When specifying equipment for a new process application, it is not only important to identify pieces of equipment that protect product integrity and are safe for end users (i.e. consumers and patients), but also ensure the safety of equipment users and operators. A major safety concern in industrial plants is the occurrence of fires and explosions. In fact, no other aspect of industrial safety has more codes and standards dedicated to it. The Occupational Safety and Health Administration (OSHA) defines a hazardous location as the following:

Hazardous locations are areas where flammable liquids, gases, vapors, or combustible dusts exist in sufficient quantities to produce explosion or fire. In hazardous locations, specially designed equipment and special installation techniques must be used to protect against the explosive and flammable potential of these substances”

Summarily, and for the purposes of this blog post, a hazardous location is anywhere where things can blow up. This post will focus on Class/Division method of hazardous location classification which is the most common method used in North America. Future posts will explore alternative classification systems as well as specific product offerings designed for optimal performance in these challenging applications.

To begin, the NEC defines three distinct classes of the general nature of hazardous materials in the surrounding atmosphere. They are as follows:

Class I: Hazardous because flammable gases or vapors are present in the air in quantities sufficient to produce explosive or ignitable mixtures

Class II: Hazardous because combustible or conductive dusts are present.

Class III: Hazardous because ignitable fibers or flyings are present, but not likely to be in suspension in sufficient quantities to produce ignitable mixtures. Typical examples are wood chips, cotton, flax, and nylon.

The division, the designation which follows the class, defines the probability of hazardous material being present in an ignitable concentration in the surrounding atmosphere. The NEC defines the following divisions:

Division 1: The substance referred to by class is present during normal conditions.

Division 2: The substance referred to by class is present only in abnormal conditions, such as a container failure or system breakdown.
Materials are subsequently divided into different groups. Group A is acetylene, Group B is hydrogen and other combustible fuels, Group C contains carbon monoxide, and Group D has gasoline, acetone and a few others. It is not the aim of this blog to define all groups. Specific hazardous materials within each group and their automatic ignition temperatures can be found in Article 500 of the National Electrical Code. It is important to note, however, that Groups A, B, C, and D apply to class I locations, while Groups E, F, and G apply to class II locations.

In summary, hazardous locations can be described as those locations where electrical equipment might installed and might present a condition which could become explosive if the elements for ignition are present. By understanding the location classification, we will be able to properly select and install equipment that can be safely operated in your process. Holland has over 60 years of specifying equipment for these challenging applications. Contact a Holland representative today for more information about your hazardous location equipment requirements and our explosion proof offerings.