Class III
locations are those which are hazardous due to the presence of easily ignitable fibers or flyings. A
fiber
is a larger particle, an example would be a carpet or clothing material fiber. An example of a
flying
would be sawdust particles ‘flying away’ from a table saw in a carpentry or woodworking shop.
The particles in Class III locations are larger than 420 µm (420 microns), and being this size, they will settle out of the air quickly. These fibers and flyings are not likely to be suspended in the air, but can collect around or on machinery, or lighting fixtures where heat, a spark or hot metal can ignite them.
While ignitable fibers and flyings present a serious fire risk, they do not normally create an explosion hazard. The greater danger with Class III materials is from the accumulation of ignitable particles over time. If a layer forms throughout a facility, an ignition can cause a flash fire which moves at near explosive speeds.
Class III - Divisions I & II
A
Class III, Division I
is a location in which easily ignitable fibers or materials producing combustible flyings are handled, manufactured or used. In Class III, Division I locations, the fibers or flyings are in the same area as the machinery that produces them.
A
Class III, Division 2
is a
location in which easily ignitable fibers are stored, or handled other than in the process of manufacture. In Class III, Division II locations, the fibers or flyings are NOT in the same area as the machinery that produces them.
