UN/NA Number Reference
DOT Class 2.3 Toxic Gas placard

UN 3520: Chlorine, adsorbed

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 3520 is assigned the proper shipping name Chlorine, adsorbed 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, 5.1, 8.

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 124)

Hazards: TOXIC. Oxidizer. May accelerate fire. Corrosive. May cause severe burns.

Fire: Use water spray or fog. Do not use dry chemical or CO2. Cool containers.

Spill: Do not touch. Stop leak if safe. Keep combustibles away from spilled material.

Chemical and Physical Properties

Chlorine appears as a greenish yellow gas with a pungent suffocating odor. Toxic by inhalation. Slightly soluble in water. Liquefies at -35 °C and room pressure. Readily liquefied by pressure applied at room temperature. Contact with unconfined liquid can cause frostbite by evaporative cooling. Does not burn but, like oxygen, supports combustion. Long-term inhalation of low concentrations or short-term inhalation of high concentrations has ill effects. Vapors are much heavier than air and tend to settle in low areas. Contact CHEMTREC to activate chlorine response team 800-424-9300. Used to purify water, bleach wood pulp, and to make other chemicals. Rate of onset: Immediate to hours Persistence: Minutes to hours Odor threshold: 3.5 ppm Source/use/other hazard: Cleaner/disinfectant in many industries; water treatment; WWI war gas; irritating corr fumes heavier than air.

CAS Number: 7782-50-5
Molecular Formula: Cl2
Molecular Weight: 70.90 g/mol
Color / Form: Yellowish-green gas
Odor: Suffocating odor
Boiling Point: -30 F
Melting Point: -150 °F (EPA, 1998)
Autoignition: Not flammable (USCG, 1999)
Specific Gravity: 1.424 (sinks in water)
Vapor Pressure: 7600 mmHg
Vapor Density: 2.49 (heavier than air)
Water Solubility: 0.7 % (NIOSH, 2024)

Regulatory Data

CERCLA RQ (40 CFR 302.4)
10 lb
EPCRA TPQ (40 CFR 355)
100 lb
OSHA PEL
(C) 1 (C) 3 0.5 ppm (ST) 1 ppm
NIOSH REL
C 0.5 ppm (1.45 mg/m 3 ) [15-minute]
IDLH
10 ppm

A release of this material at or above its CERCLA reportable quantity (10 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, N86. 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 3520 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.