USA Banner

Official US Government Icon

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure Site Icon

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #98-0347 ([Ms. Denise M. Oas])

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name:

Individual Name: Ms. Denise M. Oas

Location State: MO Country: US

View the Interpretation Document

Response text:

January 5, 2000


Ms. Denise M. Oas                                 Ref. No. 98-0347
P.O. Box 7377
North Kansas City, MO 64116

Dear Ms. Oas:

This is in response to your letter concerning a provision in 49 CFR 173.33(a)(2). This provision restricts a person from loading or accepting different materials on the same multi-unit cargo tank motor vehicle if, as a result of any mixture of the materials, an unsafe condition would occur such as an explosion, fire, excessive increase in pressure or heat, or the release of toxic vapors.  I apologize for the delay in responding and regret any inconvenience it may have caused.

In your letter, you referred to a statement published in the June 17, 1991 Federal Register publication in which we stated that the restriction in § 173.33(a)(2) was not intended to prevent the shipment of materials that, if mixed, would produce a moderate exothermic reaction that would not start a fire, rupture the tank or release acutely toxic vapors.  You asked if this interpretation is correct and if, not, just how much of an increase in pressure or heat is permitted before creating a violation of this section.

The above interpretation is correct.  In addition to meeting the provision in § 173.33(a)(2), cargo tanks must meet the general requirements for all bulk packagings in § § 173.24 and 173.24b. Under § 173.24(b), a package used for the shipment of hazardous materials must be designed, constructed, maintained, filled, its contents so limited, and closed, so that under conditions that normally occur in transportation: 1) there will be no identifiable release of hazardous materials to the environment; 2) the effectiveness of the packaging will not be substantially reduced; and 3) there will be no mixture of gases or vapors in the package which could through any credible spontaneous increase of heat or pressure, significantly reduce the effectiveness of the packaging.

Many factors affect how materials may react with each other.  They include the chemical composition and properties of the materials involved, and how they react to air, water, contaminants, or temperature conditions during transportation.  Because there are so many variables, under the Hazardous Materials Regulations, the parties involved must evaluate the potential risk posed by different materials that are offered and accepted for transportation on the same multi-tank cargo tank motor vehicle.  If your client has specific questions on making these determination, Your client may contact Mr. Charles
Hochman, Office of Hazardous Materials Technology, at (202) 366-4545 for assistance.

I hope this satisfies your request.



Hattie L. Mitchell, Chief
Regulatory Review and Reinvention
Office of Hazardous Materials Standards


Regulation Sections

Section Subject
173.33 Hazardous materials in cargo tank motor vehicles