NIOSH Publication No. 2005-151:

NIOSH Pocket Guide to Chemical Hazards

September 2005

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 See: 74931
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
Incompatibilities & Reactivities

Strong oxidizers, bleaches, copper, aluminum, nickel-copper alloys
Measurement Methods
NIOSH 2542; OSHA 26
See: NMAM or OSHA Methods
Personal Protection & Sanitation
(See protection)
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 wash
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
Important additional information about respirator selection
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   See ICSC CARD: 0299   See MEDICAL TESTS: 0144