UN/NA Number Reference
DOT Class 4.1 Flammable Solid placard

UN 1326: Hafnium powder, wetted

49 CFR 172.101 Hazardous Materials Table·ERG 2024

DOT Classification and Shipping

UN 1326 is assigned the proper shipping name Hafnium powder, wetted in the U.S. DOT Hazardous Materials Table (49 CFR 172.101). It is classified as a Class 4.1 Flammable Solid material, Packing Group II. Required label(s): 4.1.

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 170)

Hazards: Flammable. May react with water producing flammable hydrogen gas. May reignite after extinguishing.

Fire: DO NOT use water, foam, or CO2. Use dry sand, dry sodium chloride powder, or Met-L-X.

Spill: Do not touch. Cover with dry sand or earth. Keep dry. Do not use water.

Chemical and Physical Properties

Hafnium powder, dry, is a grayish metallic colored powder. Dust from dry powder may be ignited by static electricity. The dry powder reacts with moisture to produce hydrogen, a flammable gas. The heat from this reaction may be sufficient to ignite the hydrogen. It does not appreciably react with large quantities of water.

CAS Number: 7440-58-6
Molecular Formula: Hf
Molecular Weight: 178.49 g/mol
Color / Form: Gray crystals
Boiling Point: 8316 F
Melting Point: 4041 °F (NIOSH, 2024)
Autoignition: 20 °C for dust cloud
Specific Gravity: 13.31
Vapor Pressure: 0 mmHg
Water Solubility: Insoluble in water

Regulatory Data

OSHA PEL
TWA 0.5 mg/m 3 [*Note: The PEL also applies to other hafnium compounds (as Hf).]
NIOSH REL
TWA 0.5 mg/m 3 [*Note: The REL also applies to other hafnium compounds (as Hf).]
IDLH
50 mg/m 3 (as Hf)

Special Provisions

49 CFR 172.102 special provision codes for this entry: A6, A19, A20, IB6, IP2, N34, T3, TP33, W31, W40. 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.