UN/NA Number Reference

UN 1064: Methyl mercaptan

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 1064 is assigned the proper shipping name Methyl mercaptan in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 2.3 Toxic Gas material. Required label(s): 2.3, 2.1.

Packing group indicates the degree of danger within a hazard class: PG I is high danger, PG II medium, PG III low. The proper shipping name, hazard class, UN number, and packing group together form the basic shipping description that must appear on shipping papers and, where required, on the package and placard.

Emergency Response (ERG Guide 117)

Hazards: TOXIC. May be fatal if inhaled. Extremely flammable. Vapors heavier than air.

Fire: Do not extinguish unless flow stopped. Water spray to cool containers. Fight from maximum distance.

Spill: Fully encapsulating gas-tight suits required. Do not touch. Stop leak if safe.

Chemical and Physical Properties

Methyl mercaptan appears as a colorless low-boiling liquid that is denser than water. Very toxic by inhalation. Can be absorbed through the skin. Has a sharp odor, but the sense of smell cannot be relied upon to warn of the presence of vapors at low concentrations. Rate of onset: Immediate Persistence: Minutes to hours Odor threshold: 0.002 ppm Source/use/other hazard: From decayed organic matter - pulp mills, oil refineries; highly flammable; liquid burns/frostbite.

CAS Number: 74-93-1

Molecular Formula: CH4S

Molecular Weight: 48.11 g/mol

Color / Form: Water-white liquid when below boiling point, or colorless gas

Odor: Odor of rotten cabbage

Boiling Point: 42.7 F

Melting Point: -189.4 °F (EPA, 1998)

Flash Point: 0 F

Specific Gravity: 0.892 (floats on water)

Vapor Pressure: 1 to 400 mmHg at -131.26 to 44.24 F

Vapor Density: 1.66 (heavier than air)

Water Solubility: 2 %

Regulatory Data

CERCLA RQ (40 CFR 302.4)

100 lb

EPCRA TPQ (40 CFR 355)

500 lb

OSHA PEL

C 10 ppm (20 mg/m 3 )

NIOSH REL

C 0.5 ppm (1 mg/m 3 ) [15-minute]

IDLH

150 ppm

RCRA Waste Code(s)

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A release of this material at or above its CERCLA reportable quantity (100 lb) requires immediate notification to the National Response Center at 800-424-8802.

Special Provisions

49 CFR 172.102 special provision codes for this entry: 3, B7, B9, B14, N89, T50. These codes modify the general requirements (packaging, quantity limits, exceptions) for this specific material. Look up each code in 49 CFR 172.102 for the full text.

Need the full interactive record? Open UN 1064 in the SpillNerd lookup tool for the live database entry with placard graphics, GHS pictograms, full segregation tables, and synonym search. For another material, use the UN number and chemical lookup.

Reference data compiled from the DOT Hazardous Materials Table (49 CFR 172.101), the 2024 Emergency Response Guidebook, and public chemical databases (PubChem, NIOSH, EPA). Always verify the correct shipping description against the current regulation and the manufacturer's SDS Section 14 before shipping.