Zone 21 is an area in which combustible dust is likely to occur in normal operation, and Zone 22 is an area in which combustible dust is not likely to occur in normal operation and, if it occurs, will exist only for a short period.
Zone 21 is an area in which combustible dust is likely to occur in normal operation, and Zone 22 is an area in which combustible dust is not likely to occur in normal operation and, if it occurs, will exist only for a short period.