Hazmat Basics: Using Overpacks to Ship Hazardous Materials

Posted on 9/4/2020 by Roger Marks and C.L. Smith

Lion teams up with hazmat packaging provider C.L. Smith to cover the basics you must know to ship hazardous materials in an overpack. 

When I first attended hazmat training years ago and heard the word “overpack,” I thought it meant stuffing too much stuff into a single package. As in “Wow, I really overpacked this box!”

If you ship hazardous materials, you probably know that I was wrong.

hazmat overpackUS DOT’s Hazardous Materials Regulations (HMR) define an overpack as “an enclosure that is used by a single consignor to provide protection or convenience in the handling of a package or to consolidate two or more packages” [49 CFR 171.8].

In plain English, an overpack is something you put your package inside of to make it easier and safer to handle and transport.  An overpack can be a protective outer packaging like a box or a crate. If you’ve ever shrink-wrapped or banded a pallet of packages or drums together, you’ve created an overpack.

Overpacks are a simple concept, but there are some requirements you should know when you use one. Improper packaging and other easy-to-avoid mistakes can lead to rejected shipments, shipping delays, emergency releases, liability, and DOT PHMSA civil penalties now as high as $81,993 per violation.

Double Down: Repeating Marks and Labels on Overpacks

When you use an overpack, employees and supply chain personnel must be able to tell what’s inside without opening it up or breaking it apart. This means that if the required markings and/or labels are not visible through your overpack, they must be repeated on the overpack itself.

You must reproduce the following on the overpack, when applicable:
  • Proper shipping name
  • UN or NA ID number
  • Orientation arrows on two opposite vertical sides (When required by 49 CFR 172.312)
  • All hazmat markings and labels required
In addition, the word OVERPACK must be marked on the overpack when hazmat marks and labels are not visible through it. The letters must be at least 12 mm (0.5 inches) high [49 CFR 173.25(a)(4), IATA, IMDG].

Note: For ground shipments, the "OVERPACK" marking is only required when the materials inside the overpack require UN-specification packaging. 

A note from CL Smith’s packaging experts: C.L. Smith’s overpack boxes are printed with “OVERPACK” text in the required size to ensure compliance with the HMR, as well as orientation marks (up arrows) required when overpacking liquid hazardous materials.

Only Overpack Complete Hazmat Packages

hazmat overpack drawingTransporters do sometimes break up overpacks due to space considerations. This is especially common in air transport.

Because this happens, every hazmat package placed in an overpack must be “complete.” In other words, you must choose an approved packaging and your material must be packaged properly. Every package inside of an overpack must be closed per the manufacturer’s instructions, and all required marks and labels must be visible. Each package in an overpack must comply with quantity limits for the material as well.

The overpack should not function as your primary hazmat packaging. It is only there to add extra protection and make the shipment easier to handle.

What Not to Overpack

Incompatible hazardous materials may not be placed in the same overpack. If one or more packages within the overpack fails and two incompatible materials mix, the consequences could be disastrous.

If you are ever unsure whether two materials are compatible or incompatible, you can refer to the Segregation Table for Hazardous Materials found at 49 CFR 177.848.

Does My Overpack Need to Meet UN Specifications?

While the hazmat packages within your overpack must be prepared according to regulation, including using specification packaging when required, overpacks themselves are not subject to UN specifications.

That said, using a tested UN-specification packaging as your overpack provides additional protection for your goods against rigors of transportation.

A note from C.L. Smith’s packaging experts: C.L Smith offers the highest quality fiberboard overpack boxes available in the market. These overpack boxes utilize double-wall construction to provide outstanding protection throughout the supply chain.

In addition to being used for added protection of hazardous materials shipments, overpack boxes are used by carriers who ship UN rated single packagings, particularly in the parcel environment. C.L. Smith’s overpack boxes make it simple to comply with these requirements. 

Visit C.L. Smith's Website

Hazmat Training for Packagers

Under 49 CFR Part 172.704, US DOT PHMSA requires hazmat training for all “hazmat employees.”
hazmat employee is defined as any employee who, in the course of their work, can impact the safety of hazardous materials in transport.

Employees who package hazardous materials or place packages in an overpack can certainly impact the safety of the shipment, and therefore must receive adequate hazmat training. To learn more about who needs hazmat training and what’s required, check out the Hazmat Training FAQ at

By using an overpack, you make your hazardous materials easier to handle and provide an extra layer of protection. By following these few key requirements, you can ensure your overpacks arrive to their destination safely, on time, and in compliance.

Questions about overpacks? Contact the hazmat packaging specialists at C.L. Smith today or visit 

Tags: hazmat packaging, hazmat shipping, hazmat training, overpacks

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