Class I, Division I: These are harsh environments where flammable gases and chemical vapors exist. Class I, Division II: These are common areas that have volatile flammable liquids or flammable gases. These harsh industrial environments need a ventilation system rated for hazardous locations. Class II, Division I: These are hazardous areas that have a presence of combustible dust. Class II, Division II: These are areas where the combustible dust in the surrounding air could potentially result in the malfunctioning of the machinery. Class III, Division I: Any area where flammable materials or fibers are manufactured. Class III, Division II: Any area where flammable materials or fibers are stored.