A highly hazardous chemical, also called a harsh chemical, is a substance classified by the American Occupational Safety and Health Administration as material that is both toxic and reactive and whose potential for human injury is high if released. Highly hazardous chemicals may cause cancer, birth defects, induce genetic damage, cause miscarriage, injury and death from relatively small exposures.
As of August 21st, 2025, the highly hazardous chemicals list includes:
Chemical CAS number Threshold quantity (lbs)Acetaldehyde75-07-02500Acrolein107-02-8150Acryloyl chloride814-68-6250Allyl chloride107-05-11000Allylamine107-11-91000AlkylaluminumVaries5000Ammonia, anhydrous7664-41-710000Ammonia solutions (greater than 44% ammonia by weight)7664-41-715000Ammonium perchlorate7790-98-97500Ammonium permanganate7787-36-27500Arsine7784-42-1100Bis(chloromethyl) ether542-88-1100Boron trichloride10294-34-52500Boron trifluoride7637-07-2250Bromine7726-95-61500Bromine chloride13863-41-71500Bromine pentafluoride7789-30-22500Bromine trifluoride7787-71-5150003-Bromopropyne106-96-7100tert-Butyl hydroperoxide75-91-25000tert-Butyl perbenzoate614-45-97500Carbonyl chloride75-44-5100Carbonyl fluoride353-50-42500Cellulose nitrate (concentration greater than 12.6% nitrogen)9004-70-02500Chlorine7782-50-51500Chlorine dioxide10049-04-41000Chlorine pentafluoride13637-63-31000Chlorine trifluoride7790-91-21000Chlorodiethylaluminum96-10-650001-Chloro-2,4-dinitrobenzene97-00-75000Chloromethyl methyl ether107-30-2500Chloropicrin76-06-2500Chloropicrin and methyl bromide mixtureNone1500Chloropicrin and methyl chloride mixtureNone1500Cumene hydroperoxide80-15-95000Cyanogen460-19-52500Cyanogen chloride506-77-4500Cyanuric fluoride675-14-9100Diacetyl peroxide (concentration greater than 70%)110-22-55000Diazomethane334-88-3500Dibenzoyl peroxide94-36-07500Diborane19287-45-7100tert-Dibutyl peroxide110-05-45000Dichloroacetylene7572-29-4250Dichlorosilane4109-96-02500Diethylzinc557-20-010000Disopropyl peroxydicarbonate105-64-67500Dilauroyl peroxide105-74-87500Dimethyldichlorosilane75-78-510001,1-Dimethylhydrazine57-14-71000Dimethylamine, anhydrous124-40-325002,4-Dinitroaniline97-02-95000Ethyl Methyl Ketone Peroxide (also Methyl Ethyl Ketone Peroxide; concentration >60%)1338-23-45000Ethyl nitrite109-95-55000Ethylamine75-04-77500Ethylene fluorohydrin371-62-0100Ethylene Oxide75-21-85000Ethyleneimine151-56-41000Fluorine7782-41-41000Formaldehyde (formalin)50-00-01000Furan110-00-9500Hexafluoroacetone684-16-25000Hydrochloric acid, anhydrous7647-01-05000Hydrofluoric acid, anhydrous7664-39-31000Hydrogen bromide10035-10-65000Hydrogen chloride7647-01-05000Hydrogen cyanide, anhydrous74-90-81000Hydrogen fluoride7664-39-31000Hydrogen peroxide (52% by weight or greater)7722-84-17500Hydrogen selenide7783-07-5150Hydrogen sulfide7783-06-41500Hydroxylamine7803-49-82500Iron pentacarbonyl13463-40-6250Isopropylamine75-31-05000Ketene463-51-4100Methacrylaldehyde78-85-31000Methacryloyl chloride920-46-7150Methacryloyloxyethyl isocyanate30674-80-7100Methyl acrylonitrile126-98-7250Methylamine, anhydrous74-89-51000Methyl bromide74-83-92500Methyl chloride74-87-315000Methyl chloroformate79-22-1500Methyl ethyl ketone peroxide1338-23-45000Methyl fluoroacetate453-18-9100Methyl fluorosulfate421-20-5100Methyl hydrazine60-34-4100Methyl iodide74-88-47500Methyl isocyanate624-83-9250Methyl mercaptan74-93-15000Methyl vinyl ketone79-84-4100Methyltrichlorosilane75-79-6500Nickel carbonyl13463-39-3150Nitric acid (94.5% by weight or greater)7697-37-2500Nitric oxide10102-43-9250para-Nitroaniline100-01-65000Nitromethane75-52-52500Nitrogen dioxide10102-44-0250Nitrogen oxides (NO; NO2; N2O4; N2O3)10102-44-0250Nitrogen tetroxide10544-72-6250Nitrogen trifluoride7783-54-25000Nitrogen trioxide10544-73-7250Oleum (65% to 80% by weight)8014-95-71000Osmium tetroxide20816-12-0100Oxygen difluoride7783-41-7100Ozone10028-15-6100Pentaborane19624-22-7100Peracetic acid (concentration greater than 60%)79-21-01000Perchloric acid (concentration greater than 60% by weight)7601-90-35000Perchloromethyl mercaptan594-42-3150Perchloryl fluoride7616-94-65000Phosgene75-44-5100Phosphine7803-51-2100Phosphorus oxychloride10025-87-31000Phosphorus trichloride7719-12-21000Phosphoryl chloride10025-87-31000Propargyl bromide106-96-7100Propyl nitrate627-3-42500Sarin107-44-8100Selenium hexafluoride7783-79-11000Stibine7803-52-3500Sulfur dioxide (liquid)7446-09-51000Sulfur pentafluoride5714-22-7250Sulfur tetrafluoride7783-60-0250Sulfur trioxide7446-11-91000Sulfuric anhydride7446-11-91000Tellurium hexafluoride7783-80-4250Tetrafluoroethylene116-14-35000Tetrafluorohydrazine10036-47-25000Tetramethyl lead75-74-11000Thionyl chloride7719-09-7250Trichloro(chloromethyl)silane1558-25-4100Trichloro(dichlorophenyl)silane27137-85-52500Trichlorosilane10025-78-25000Trifluorochloroethylene79-38-910000Trimethoxysilane2487-90-31500
External links OSHA list of highly hazardous chemicals