Many manufacturers employ systems of interconnected piping, pumps, accumulators, filters, heat exchangers, etc. and associated control systems in their operations. Often, these systems control processes using gases such as nitrogen or argon. This requires that technologies not only deliver the right pressures and volumes, but must also consider the safety features that accompany such conditions in the presence of electricity.
Electrical equipment installation in atmospheres with flammable gases or vapors, flammable liquids, combustible dusts, ignitable fibers or filings represent a risk for fire and explosion. Areas with possible fire or explosion risks due to explosive atmospheres and/or mixtures are called hazardous (or classified) locations or areas. In the U.S. and Canada, these areas have historically been classified with the Class/Division system. In Europe and the rest of the world—and also increasingly in North America—the Zone system is used. The hazardous area classification system determines required protection techniques and methods for electrical and other spark-creating installations in the location.
The Class/Division/Group system is based on the National Electrical Code (NEC) where:
- Classes define the general nature of the hazardous material in the surrounding atmosphere.
- Divisions define the probability of hazardous material being present in the surrounding atmosphere.
- Groups define the type of the hazardous material in the surrounding atmosphere.
We quite often see applications where a prospective user calls for conditions that fit into a Class I environment and sometimes unknowingly find themselves also specifying a Division 1 (Class I/Div. 1) scenario where the configuration is particularly hazardous because flammable gases or vapors are present (or may be present) in quantities sufficient to produce explosive or ignitable mixtures. Extra care and specific cautions have to be taken to protect the process and primarily the people around the equipment; risk of serious danger can be high. We get concerned and consider the case to be Div. 1 when the substance referred to by class has a high probability of producing an explosive or ignitable mixture due to it being present continuously, intermittently or periodically, or from the equipment itself under normal operating conditions.
Choices for safeguards and personal protective equipment (PPE) are very critical at this point, and exacting material specifications and controls play a big part in planning for and mitigating the safety protocols used in design and operation. It requires specialized knowledge and expertise to engineer and build a compliant and inherently safe system. Matching the specific conditions of one’s process and equipment design to the optimal set of safety options is a function of experience and knowledge, using good resources and best practices. Some widely used protection schemes and techniques for protecting workers and equipment include:
- Dust ignition-proof
- Explosion-proof
- Intrinsically safe
- Non-incendive
One of the most widely accepted and expected means to properly control and accommodate these risks is through the use of intrinsically safe components and in the design and configuration of a system where such risks are expected to be present. An intrinsically safe component is incapable of releasing sufficient electrical or thermal energy to cause ignition of a specific hazardous substance under normal or abnormal (fault) operating conditions; this means that intrinsically safe equipment and wiring will limit electrical and thermal energy to a level below that required to cause or start an explosion. Knowing what components to specify and how to properly use them in a design is where experts such as process engineers, programmers, designers and fabricators contribute so much to successful systems.
Steven E. Beyer is general manager at Optimation Technology Inc., a certified member of the Control System Integrators Association (CSIA). For more information about Optimation Technology, visit its profile on the Industrial Automation Exchange.
