US Occupational Safety and Health Administration has recently revise Permissable Exposure Limits (PEL) for over 400 chemicals. For acetone this new limit is 250 ppm. Acetone belongs groups of ketone solvents, together with methyl ethyl ketone, methyl butyl ketone and methyl isobutyl ketone. It was previous ly considered the least toxic of the group, but now bearing in mind also its extreme flammability, it is suggested that it be replaced when possible with methyl ethyl ketone.