TABLE OF CONTENTS Because troubleshooting is often done in the field, and many times in electrically hazardous (classified) areas, we must be able to troubleshoot instrument systems safely in such areas. This requires a basic understanding of the methods used to put instrumentation in hazardous areas. Not only must we be able to open and interact with instrument circuits, but we must also return the equipment to its original safe state. (Obviously, if the instrumentation is mechanical or pneumatic, this is not an issue.)
Three components must be present to have a fire or explosion: (1) an oxidizer such as atmospheric oxygen, (2) a flammable material in an ignitable mixture, and (3) a source of ignition (see the fire triangle, Figure 6-1). Since oxygen in the air makes one side of the triangle readily available, and facilities that handle flammable or combustible materials can provide fuel, another side, all that is required to cause an explosion or fire, is the third side an ignition source. Electrical equipment and maintenance activities can provide the required source of ignition to complete the fire triangle.
What follows is a brief review of the principles of area classification and the methods or means of placing electrical equipment in these areas.
This section provides an overview of NEC Article 500 division-based and Article 505 zone-based classification systems.
Since electrical equipment can serve as a source of ignition, methods...
