UN/NA Number Reference
DOT Class 6.1 Toxic Substance placard

UN 2644: Methyl iodide

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 2644 is assigned the proper shipping name Methyl iodide in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 6.1 Toxic Substance material, Packing Group I. Required label(s): 6.1.

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 151)

Hazards: TOXIC. May be fatal if inhaled, ingested, or absorbed through skin. Contact may cause burns.

Fire: Use agent appropriate for surrounding fire. Cool containers with water.

Spill: Do not touch. Avoid inhalation. Use water spray to reduce dust/vapor. Ventilate.

Chemical and Physical Properties

Methyl iodide appears as a colorless liquid that turns brown on exposure to light. Denser than water. Contact may irritate skin, eyes and mucous membranes. Very toxic by ingestion, inhalation and skin absorption.

CAS Number: 74-88-4
Molecular Formula: CH3I
Molecular Weight: 141.939 g/mol
Color / Form: Colorless, transparent liquid (turns brown on exposure to light)
Odor: Pungent, ether-like odor.
Boiling Point: 108.3 F
Melting Point: -87.6 °F (NTP, 1992)
Autoignition: 355 °C
Specific Gravity: 2.279 (sinks in water)
Vapor Pressure: 661.76 mmHg
Vapor Density: 4.9 (heavier than air)
Water Solubility: 10 to 50 mg/mL at 64 F
Log P: log Kow= 1.51

Regulatory Data

CERCLA RQ (40 CFR 302.4)
100 lb
OSHA PEL
TWA 5 ppm (28 mg/m 3 ) [skin]
NIOSH REL
Ca TWA 2 ppm (10 mg/m 3 ) [skin]
IDLH
Ca [100 ppm]
RCRA Waste Code(s)
[object Object]

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: 2, B9, B14, B32, T20, TP2, TP13, TP38, TP45. 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 2644 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.