Zone 20, 21, and 22 locations are categorized by what characteristic?

Zone 20, 21, and 22 locations are defined by the presence of combustible dusts or ignitable fibers. In the context of hazardous locations, these zones are classified based on the likelihood of explosive atmospheres created by dusts, fibers, or particulates that can accumulate and ignite, especially in specific environments.

Zone 20 indicates an area where combustible dust is present continuously, while Zone 21 is where such dust might be present intermittently during normal operations, and Zone 22 refers to areas where combustible dust is not likely to be present during normal operations but may occasionally occur.

Understanding these classifications is crucial for ensuring safety and compliance with the National Electrical Code (NEC) as it helps guide the design and installation of electrical systems and equipment in environments where combustible substances are present. This categorization is essential for selecting appropriate electrical equipment designed to prevent ignition sources, thus minimizing explosion risks.

The other options, while relevant to safety and the classification of hazardous areas, do not accurately reflect the primary characteristic defining Zones 20, 21, and 22, which specifically focus on combustible dust rather than other flammable or hazardous materials.