Interpretation Response #26-0022
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
Response Publish Date:
Company Name: Air Liquide Advanced Materials
Individual Name: Guillaume Husson
Location State: NJ Country: US
View the Interpretation Document
Response text:
August 13, 2026
Guillaume Husson
Global Product Stewardship Manager
Air Liquide Advanced Materials
3040 US Highway 22
Branchburg, NJ 08876
Reference No. 26-0022
Dear Mr. Husson:
This letter is in response to your January 24, 2026 letter requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the classification of a silylamine compound. Specifically, you are seeking clarification on the classification of the chemical compound which exhibits the following hazards: Division 6.1, inhalation Hazard Zone B, Packing Group (PG) I; Division 4.3, PG I; Class 8, PG I; and Class 3, PG II. You state that, based on the precedence of hazards described in § 173.2a, your company has selected the description "UN3491, Toxic by inhalation liquid, water-reactive, flammable, n.o.s. (Silylamine compound), 6.1(4.3, 3), PG I." You further state that this description excludes the corrosive characteristics of the material, and that § 172.402(a)(2), as referenced in a previous letter of interpretation (LOI Ref No. 13-0003), mandates all materials with a Class 8, PG I subsidiary hazard be labelled with a CORROSIVE label.1 Lastly, you state that applying the CORROSIVE subsidiary hazard label when the corrosive hazard is not identified in the shipping description for UN3491 has led to frustration of your shipments because many freight forwarders and carriers rely solely on the hazard codes in the description, and they require the removal of the CORROSIVE label.
1 Air Liquide USA LLC, Letter of Interpretation Reference Number 13-0003, available at https://www.phmsa.dot.gov/regulations/title49/interp/13-0003
In accordance with § 173.22 of the HMR, it is the shipper's responsibility to properly classify hazardous materials, as this Office does not generally perform this function. However, based on the information provided in your letter, it is the opinion of this Office that the description of "UN3491, Toxic by inhalation liquid, water-reactive, flammable, n.o.s. (Silylamine compound), 6.1 (4.3, 8, 3), PG I" is correct. For transport within the United States, § 172.402(a)(2) requires all hazardous materials with a Class 8, PG I, subsidiary hazard to be labeled with a subsidiary CORROSIVE hazard warning label in all modes of transport. Therefore, the subsidiary hazard class must be entered in the proper shipping description as well (see § 172.202(a)(3)).
I hope this information is helpful. Please contact us if we can be of further assistance.
Sincerely,
Alexander Wolcott
Acting Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division