These limits are intended for use in the field of industrial hygiene and should be interpreted and applied by persons trained in thin field. They are not intended for use (or modification for use) (1) as ratios of two limits, (2) in the evaluation or control of community air-pollution nuisances, (3) in estimating the toxic potential of continuous uninterrupted exposures, (4) as proof or disproof of existing diseases or physical conditions, or (5) for adoption by countries whose working conditions differ from those in the United States and where substances and processes differ