# NIOSH Pocket Guide to Chemical Hazards
Methyl mercaptan | CAS 74-93-1
CH3SH | RTECS PB4375000
Synonyms & Trade Names Mercaptomethane, Methanethiol, Methyl sulfhydrate | DOT ID & Guide 1064 117
Exposure Limits | NIOSH REL: C 0.5 ppm (1 mg/m3) [15-minute]
OSHA PEL†: C 10 ppm (20 mg/m3)
IDLH 150 ppm | Conversion 1 ppm = 1.97 mg/m3
Physical Description Colorless gas with a disagreeable odor like garlic or rotten cabbage. [Note: A liquid below 43°F. Shipped as a liquefied compressed gas.]
MW: 48.1 | BP: 43°F | FRZ: -186°F | Sol: 2%
VP: 1.7 atm | IP: 9.44 eV | RGasD: 1.66 | Sp.Gr: 0.90 (Liquid at 32°F)
Fl.P: NA (Gas) (oc) 0°F (Liquid) | UEL: 21.8% | LEL: 3.9% |
Flammable Gas Class IA Flammable Liquid
Incompatibilities & Reactivities Strong oxidizers, bleaches, copper, aluminum, nickel-copper alloys
Measurement Methods NIOSH 2542; OSHA 26
Personal Protection & Sanitation Skin: Prevent skin contact (liquid)/Frostbite Eyes: Prevent eye contact (liquid)/Frostbite Wash skin: No recommendation Remove: When wet (flammable) Change: No recommendation Provide: Eyewash (liquid), Quick drench (liquid), Frostbite | First Aid (See procedures) Eye: Irrigate immediately (liquid)/Frostbite Skin: Water flush immediately (liquid)/Frostbite Breathing: Respiratory support
Respirator Recommendations NIOSH Up to 5 ppm: (APF = 10) Any chemical cartridge respirator with organic vapor cartridge(s)/(APF = 10) Any supplied-air respirator Up to 12.5 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 25 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 supplied-air respirator that has a tight-fitting facepiece and is operated in a continuous-flow mode/(APF = 50) Any self-contained breathing apparatus with a full facepiece/(APF = 50) Any supplied-air respirator with a full facepiece Up to 150 ppm: (APF = 1000) Any supplied-air respirator 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, skin and/or eye contact (liquid)
Symptoms Irritation eyes, skin, respiratory system; narcosis; cyanosis; convulsions; liquid: frostbite
Target Organs Eyes, skin, respiratory system, central nervous system, blood
See also: INTRODUCTION