UN/NA Number Reference
DOT Class 2.1 Flammable Gas placard

UN 1055: Isobutylene

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 1055 is assigned the proper shipping name Isobutylene in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 2.1 Flammable Gas material. Required label(s): 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 115)

Hazards: Extremely flammable. May be ignited by heat, sparks, or flames. Vapors may travel to ignition source and flash back. Containers may rocket or BLEVE.

Fire: Do not extinguish unless flow can be stopped. Use water spray to cool containers. Move containers from fire if safe.

Spill: Eliminate ignition sources. Stop leak if safe. Use water spray to reduce vapors.

Chemical and Physical Properties

Isobutylene is a colorless gas with a faint petroleum-like odor. For transportation it may be stenched. It is shipped as a liquefied gas under its own vapor pressure. Contact with the liquid can cause frostbite. It is easily ignited. Its vapors are heavier than air and a flame can flash back to the source of leak very easily. The leak can either be a liquid or vapor leak. It can asphyxiate by the displacement of air. Under prolonged exposure to fire or heat the containers may rupture violently and rocket. It is used in the production of isooctane, a high octane aviation gasoline.

CAS Number: 115-11-7
Molecular Formula: C4H8
Molecular Weight: 56.11 g/mol
Color / Form: Colorless gas
Odor: Coal gas odor
Boiling Point: 19.6 F
Melting Point: -220.5 °F (NTP, 1992)
Flash Point: -105 °F (NTP, 1992)
Autoignition: 869 °F (USCG, 1999)
Specific Gravity: 0.59 (floats on water)
Vapor Pressure: 1 mmHg at -157.2 F
Vapor Density: 1.9 (heavier than air)
Water Solubility: Insoluble
Log P: log Kow = 2.34

Special Provisions

49 CFR 172.102 special provision codes for this entry: 19, 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.

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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.