# NIOSH Pocket Guide to Chemical Hazards
Mesityl oxide | CAS 141-79-7
(CH3)2C=CHCOCH3 | RTECS SB4200000
Synonyms & Trade Names Isobutenyl methyl ketone, Isopropylideneacetone, Methyl isobutenyl ketone, 4-Methyl-3-penten-2-one | DOT ID & Guide 1229 129
Exposure Limits | NIOSH REL: TWA 10 ppm (40 mg/m3)
OSHA PEL†: TWA 25 ppm (100 mg/m3)
IDLH 1400 ppm [10%LEL] | Conversion 1 ppm = 4.02 mg/m3
Physical Description Oily, colorless to light-yellow liquid with a peppermint- or honey-like odor.
MW: 98.2 | BP: 266°F | FRZ: -52°F | Sol: 3%
VP: 9 mmHg | IP: 9.08 eV |  | Sp.Gr(59°F): 0.86
Fl.P: 87°F | UEL: 7.2% | LEL: 1.4% |
Class IC Flammable Liquid: Fl.P. at or above 73°F and below 100°F.
Incompatibilities & Reactivities Oxidizers, acids
Measurement Methods NIOSH 1301; OSHA 7
Personal Protection & Sanitation Skin: Prevent skin contact Eyes: Prevent eye contact Wash skin: When contaminated Remove: When wet (flammable) Change: No recommendation Provide: Quick drench | First Aid (See procedures) Eye: Irrigate immediately Skin: Water flush immediately Breathing: Respiratory support Swallow: Medical attention immediately
Respirator Recommendations NIOSH Up to 250 ppm: (APF = 25) Any supplied-air respirator operated in a continuous-flow mode£/(APF = 25) Any powered, air-purifying respirator with organic vapor cartridge(s)£ Up to 500 ppm: (APF = 50) Any chemical cartridge respirator with a full facepiece and organic vapor cartridge(s)/(APF = 50) Any air-purifying, full-facepiece respirator (gas mask) with a chin-style, front- or back-mounted organic vapor canister/(APF = 50) Any powered, air-purifying respirator with a tight-fitting facepiece and organic vapor cartridge(s)£/(APF = 50) Any self-contained breathing apparatus with a full facepiece/(APF = 50) Any supplied-air respirator with a full facepiece Up to 1400 ppm: (APF = 2000) Any supplied-air respirator that has a full facepiece and is operated in a pressure-demand or other positive-pressure mode Emergency or planned entry into unknown concentrations or IDLH conditions: (APF = 10,000) Any self-contained breathing apparatus that has a full facepiece and is operated in a pressure-demand or other positive-pressure mode/(APF = 10,000) Any supplied-air respirator that has a full facepiece and is operated in a pressure-demand or other positive-pressure mode in combination with an auxiliary self-contained positive-pressure breathing apparatus Escape: (APF = 50) Any air-purifying, full-facepiece respirator (gas mask) with a chin-style, front- or back-mounted organic vapor canister/Any appropriate escape-type, self-contained breathing apparatus
Exposure Routes inhalation, ingestion, skin and/or eye contact
Symptoms Irritation eyes, skin, mucous membrane; narcosis, coma; in animals: liver, kidney damage; central nervous system effects
Target Organs Eyes, skin, respiratory system, central nervous system, liver, kidneys
See also: INTRODUCTION