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Net Weight vs. Gross Weight in the Hazardous Material Regulations

Net Weight vs. Gross Weight in the Hazardous Material Regulations

Your compliance with the Hazardous Material Regulations (HMR) of the USDOT/PHMSA will depend upon, among other things,

  • The type of hazardous material to be shipped;
  • The method of transportation:  motor vehicle, rail car, vessel, or aircraft;
  • The type of packaging; and,
  • The weight of the packaging and/or the HazMat.

The purpose of this article is to make known the terms used by USDOT/PHMSA regarding the weight of a shipment of HazMat and its impact on compliance with the HMR.

At various places within the HMR, reference is made to the weight of the hazardous material to be shipped or the weight of the packaging to be used for its transportation.  When the determining factor is the weight of the hazardous material, and only the hazardous material, the HMR will refer to the net weight.  When the determining factor is the weight of the packaging (ie. the HazMat, container/packaging, absorbant material or dunnage, inner containers, etc.) the HMR will refer to the gross weight.

Gross weight is defined at 49 CFR 171.8:

Gross weight or Gross mass means the weight of a packaging plus the weight of its contents.

Net weight is not defined in the HMR, but the USDOT/PHMSA did make clear in an interpretation letter (98-0594):

The term gross mass is defined in § 171.8 as ‘the weight of a packaging plus the weight of its contents.’  The term ‘net mass’ means the weight of the contents in a packaging.  The difference between the two terms is the fact that you include the weight of the packaging in determining its gross mass but you do not include the weight of the packaging when determining its net mass.

Further complicating the issue are the terms “package” and “packaging”,  both of which are defined at §171.8:

Package or Outside Package means a packaging plus its contents. For radioactive materials, see §173.403 of this subchapter.

Packaging means a receptacle and any other components or materials necessary for the receptacle to perform its containment function in conformance with the minimum packing requirements of this subchapter. For radioactive materials packaging, see §173.403 of this subchapter.

So, when the term “packaging” is used in the HMR, it is referring to the weight of the receptacle (ie. container) and anything else necessary for its purpose.  When the term “package” is used, the HMR is referring to the packaging plus its contents (ie. the HazMat placed inside the packaging for shipment).

Why does this matter?  Well, let’s review a few places in the HMR where compliance depends upon the weight of the shipment:

  1. The vehicle placarding regulations of §172.504(c) allow for an exception from placarding if the aggregate gross weight of specified HazMat on the vehicle is <1,001 lbs.  Since “gross weight” is indicated, you must consider the entire weight of the packaging and the weight of the HazMat.
  2. §173.6(a)(1) limits the use of the Materials of Trade exception to certain hazardous materials, “contained in a packaging having a gross mass or capacity not over…”  The reference to “packaging” may be misleading, but the inclusion of “gross mass” clearly indicates you must consider the weight of both the packaging and the hazardous material.
  3. The transportation of NA 3178 Smokeless Powder for Small Arms is subject to the weight restrictions of §173.171, which includes a limit on the maximum weight allowed per package, “The net weight of smokeless powder in any one box (one package) must not exceed 7.3 kg (16 pounds).”  Here, the limit of 16 pounds applies to the hazardous material to be shipped and does not include the weight of the packaging.
  4. HazMat packagings are manufactured to certain design specifications and then tested to ensure they meet the standards.  The packagings must be marked by the manufacturer to indicate, among other things, the maximum gross mass of the package (for solids).  In other words, the maximum weight (packaging and contents) of the shipment must not exceed the maximum rated weight of the packaging.

There are many other instances throughout the Hazardous Material Regulations where weight is a critical factor.  Be sure you are reading the regulations carefully and fully understand the terms used by the USDOT/PHMSA.  Contact me for a free consultation or to schedule HazMat Employee Training for you and your employees.