MAY-JUN 2017

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Hazardous area installation challenges and solutions 42 INTECH MAY/JUNE 2017 WWW.ISA.ORG By Jim Dunn C ertain areas in industrial settings are classified as hazardous due to the pres- ence of flammable gases, vapors, dusts, or fibers. This article describes various ways to design these panels so they do not become po- tential ignition sources, using the International Electrotechnical Commission (IEC) zone hazard- ous area classification system for this purpose. Figure 1 depicts how the IEC zone system clas- sifies areas based on the ignitable concentrations of flammable gases or vapors. Zone 0 is the most hazardous area, followed by Zone 1, and then Zone 2. It is much more expensive, complex, and time consuming to design, fabricate, and main - tain control panels to use in Zone 0 rather than Zone 1 or 2. So, the first step is to locate control panels outside of Zone 0 areas wherever possible. This can often be accomplished by moving panels just a short distance, often as little as a few feet. Figure 2 shows a typical zone classification scheme for a process plant. Zone 0 areas are only those inside or right next to vessels or pipes, with Zone 1 areas in relatively close proximity to Zone 0, and Zone 2 areas a bit farther away. Once all panels have been located to the least restrictive zone possible, the three main design methods for compliance can be considered: l rated enclosures and components l air-purge systems l intrinsic safety practices Use Zone 1 and 2 components and enclosures Using properly rated components and enclosures is the simplest method for compliance in Zone 1 and 2, although it is not suitable for Zone 0 in most cases due to the lack of availability of Zone 0–rated components. Any control panel suitable for instal- lation in Zone 1 will also be suitable for Zone 2, so the focus of the rest of this article will be on Zone 1. The enclosure and the components should all be specified for use in Zone 1, and the panel de sign should also meet Zone 1 requirements. This method works well for smaller and simpler control panels—often referred to as control sta- tions—populated with push button, switch, and indicator light devices. However, it often does not work well for enclosures populated with more complex components, such as programmable logic controllers (PLCs), motor drives, and human- machine interfaces (HMIs), because many of these components are not available with proper ratings. For example, your company's preferred make and model PLC might not be certified for use in Zone 1. Preassembled Zone 1 standard control stations populated by an assortment of rated push but- tons, switches, and lights are available from some suppliers (figure 3). Some suppliers will build cus- tomized control stations, so end users and inte- Hazardous area installation challenges and solutions Figure 1. The IEC zone system classifies areas according to the expected presence of hazardous atmospheres. Figure 2. Control stations and panels should be located outside of Zone 0 whenever possible, which often just requires relo ca- tion to a few feet away. Zone 0 Areas in which hazardous explo- sive gas atmospheres are pres- ent constantly for long periods (e.g., in pipes or containers) Ex ia Ex s (where specially certified Zone 0) Containers Zone 1 Areas in which hazardous explo- sive gas atmospheres are occa- sionally present (e.g., areas close to pipes or draining stations) Ex d, Ex ib, Ex p, Ex e, Ex s, Ex o, Ex q, Ex m Equipment suitable for Zone 0 Zone 2 Areas in which hazardous explo- sive gas atmospheres are rare or only exist for a short time (e.g., areas close to Zones 0 and 1) Ex N/Ex n Equipment suitable for Zones 1 and 0 Suitable protection

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