How to Classify Hazmat That Changes Its Characteristics

Posted on 2/19/2013 by Lion Staff

Q. I have to ship some solid phosphoric acid powder. The Hazardous Material Table says it’s a Class 8—Corrosive hazardous material. I thought that Class 8 was only for corrosive liquids. What’s up with that?
A. A material is a Class 8 hazmat if it fails the tests given in 49 CFR 173.137. The procedures for those tests are calibrated for liquids and are not suitable for solids.
In general, you classify a hazmat based on its properties at the time you offer it for transportation. But there’s one exception to this principle—when a solid material may become a liquid during transportation, either by melting or absorbing moisture from the atmosphere, and that liquid would be a Class 8 corrosive, then the solid must be classified and otherwise managed as a Class 8 corrosive hazmat.
“A liquid, or a solid which may become liquid during transportation, that has a severe corrosion rate on steel or aluminum based on the criteria in 173.137(c)(2) is also a corrosive material.” [49 CFR 173.136(a)]
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An Example of Classifying Changing Characteristics
Take phosphoric acid for example. At room temperature, phosphoric acid is a crystalline solid, but its melting point is around 100° F. During the normal course of intermodal transportation, ambient temperatures can range from -40° to over 200° F.
This means it’s very possible for a consignment of solid phosphoric acid powder to liquefy during transport. When in a liquid phase phosphoric acid can corrode metal packagings and/or vehicles. Therefore, you must treat the solid powder as if it were a corrosive hazmat, even though it doesn’t quite meet the definition given.
In other words, if you ship a solid material that may become a Class 8 corrosive liquid during transport, it should be classified and named accordingly. So, although your material may not exhibit the characteristics of a Class 8 corrosive hazardous material when you ship it, it is correct to classify and name it as a Class 8 hazmat and package it accordingly.
How to Pack Meltable Solids
When packing solid hazardous materials that may become liquid during transport (i.e., meltable solids), there are special rules you must follow to accommodate this potential change in phase. [49 CFR 173.24 (a)(b)(3)] Specifically, the packaging must be able to contain the liquid in addition to providing enough absorbent material in the event of any damage or leakage with regard to inner packaging.
Learn all the DOT’s rules for classifying, packaging, marking, labeling, and documenting your hazmat shipments in full compliance with the Hazardous Materials Regulations at Lion’s Hazardous Materials Transportation Certification Workshop. For the full schedule, visit
What other unique hazmat classifying or packaging rules have you come across? Share below.

Tags: DOT, hazmat shipping

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