UN/NA Number Reference
DOT Class 6.1 Toxic Substance placard

UN 2662: Hydroquinone, solid

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 2662 is assigned the proper shipping name Hydroquinone, solid 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 III. 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 153)

Hazards: TOXIC. Combustible. Corrosive. Causes burns. Toxic fumes when heated.

Fire: Small: dry chemical, CO2, water spray. Large: water spray, foam.

Spill: Do not touch. Stop leak if safe. Use water spray to reduce vapor.

Chemical and Physical Properties

Hydroquinone appears as light colored crystals or solutions. May irritate the skin, eyes and mucous membranes. Mildly toxic by ingestion or skin absorption.

CAS Number: 123-31-9
Molecular Formula: C6H6O2
Molecular Weight: 110.11 g/mol
Color / Form: White crystals
Odor: Odorless
Boiling Point: 549 F
Melting Point: 338 to 340 °F (EPA, 1998)
Flash Point: 329 F
Autoignition: 960 °F (USCG, 1999)
Specific Gravity: 1.332
Vapor Pressure: 4 mmHg
Vapor Density: 3.81 (heavier than air)
Water Solubility: 10 to 50 mg/mL at 68 °F (NTP, 1992)
Log P: 0.59

Regulatory Data

CERCLA RQ (40 CFR 302.4)
100 lb
EPCRA TPQ (40 CFR 355)
500 lb
OSHA PEL
........ 2 2 mg/m 3
NIOSH REL
C 2 mg/m 3 [15-minute]
IDLH
50 mg/m 3

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.

Need the full interactive record? Open UN 2662 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.