It should be noted, however, that almost all chlorinated hydrocarbons have been found to be toxic to some degree. The current threshold limit value for carbon tetrachloride is 5 ppm. It is also provided as a solid polymer that decomposes to its monomer upon heating. It is a suspected human carcinogen and inhalation of the vapors may result in severe irritation of the upper respiratory tract and edema. Formaldehyde is a severe eye irritant, causing delayed effects that are not appreciably eased by eye washing.
Skin sensitization can result from repeated exposure.
Laboratory operations with formalin in open vessels should be carried out in a fume hood. Because repeated exposure to formaldehyde can lead to a formaldehyde allergy, it is well to avoid skin contact with aqueous solutions by appropriate use of neoprene, butyl rubber, or polyvinyl chloride gloves. Splash-proof goggles must be worn to avoid any possibility of splashing formaldehyde in the eyes. The current threshold limit value for formaldehyde is 1 ppm. Perchloric Acid Perchloric acid is a water white liquid, with no odor.