When you select packaging for a regulated product, finding a pail that’s the right size is only the beginning. Two plastic pails can look nearly identical on the outside and still serve very different applications, and that distinction matters most with hazardous materials, where the pail, lid, closure method, and tested configuration work together as one complete, certified package.
Two plastic pails can look nearly identical on the outside and still be designed and certified for very different applications. That distinction is especially important when hazardous materials are involved, where the pail, lid, closure method, and tested configuration all work together as a complete package.
Our Traditional M2 and M4 pails are a good example.
Both belong to our Traditional Pail family. We manufacture both from FDA-grade raw materials, equip both with metal or plastic handles and similar fittings, and offer Offset or Heat Transfer printing on both. But when it comes to their closure designs and UN certifications, there are important differences.
Understanding those differences can help you determine which configuration may be appropriate for your product.
M2 and M4: Similar Pails, Different Closures
One of the easiest ways to distinguish the Traditional M2 and M4 is by looking at the lid.
The M2 uses a grip-and-rip tear-tab lid, which gives you a straightforward method for accessing the contents once you’ve applied the cover.
The M4 uses a non-tear-tab, pressed-on cover.
That difference may sound small, but the closure method is part of the testing for the UN package. Our UN/DOT documentation identifies the configurations as M2 pail and M2 lid (tear-tab lid) and M4 pail and M4 lid (non-tear-tab lid), and each configuration requires the correct lid to meet the applicable UN/DOT performance-oriented packaging standards.
In other words, UN certification applies to the tested packaging configuration, not simply the pail itself.
The M2: Built Around UN-Certified Solids Configurations
For applications involving qualifying hazardous solids, the M2 offers a broad range of sizes:
- 1.0 gallon
- 2.0 gallon
- 3.5 gallon
- 4.25 gallon
- 5.0 gallon
- 5.3 gallon
- 6.0 gallon
- 6.5 gallon
Across the configurations we document, the M2 is certified for solids, with the specific UN marking and authorized gross mass varying by pail size.
A solids UN marking may include an “S,” which indicates that the package has been tested for solids or inner packagings rather than as a single packaging for liquids.
The M4: When the Application Involves Liquids
The Traditional M4 comes in fewer sizes, but its UN capabilities address something the M2 configurations do not: hazardous liquids.
M4 options are available in:
- 3.5 gallon
- 4.25 gallon
- 5.0 gallon
- 5.3 gallon
Our certification documentation includes M4 configurations carrying UN liquid ratings for Packaging Groups II and III. Certain M4 configurations also carry certifications for solids, so it’s important to look at the specific size and UN marking rather than assuming every M4 has the same certification.
The 5.0-gallon M4 liquid test report helps illustrate the difference. The tested package underwent drop testing, leak proofness testing, and internal hydrostatic pressure testing, including a 30 kPa internal hydrostatic pressure test.
Why Are UN Tests Different for Solids and Liquids?
Think about what happens if a package is dropped during transportation.
With a solid product, the package must contain its contents and withstand the forces the impact creates. Our 6.5-gallon M2 solids testing, for example, includes drop testing in multiple orientations as well as stacking and stability testing.
Liquids introduce additional considerations, including pressure and leakage. A liquid can exert force against the package and its closure in ways a solid product does not, which is why liquid packaging testing can include requirements such as leak proofness and hydrostatic pressure testing.
The M2 and M4 may look similar, but their testing and certifications reflect the different demands placed on the complete package.
Reading the UN Mark Tells You More Than “Certified”
Simply seeing a UN symbol on the bottom of a pail doesn’t tell the whole story.
Consider the difference between:
1H2/Y27/S
and
1H2/Y1.5/30
For these examples, 1H2 identifies an open-head plastic drum or pail. From there, the marking changes based on what the package has been certified to contain.
For a solids marking, the number associated with the certification represents the maximum gross mass in kilograms, followed by S for solids.
A liquid marking instead identifies the maximum specific gravity associated with the certification and includes the applicable hydrostatic test pressure.
The UN marking therefore tells you the specific performance level and application for which that packaging configuration was tested.
The Complete Configuration Matters
The difference between the M2 and M4 isn’t just the pail body or the style of lid. UN certification applies to the complete tested configuration.
That means you can’t simply switch lids, fittings, or other specified components and assume the original certification still applies. You must assemble the package according to the applicable closure instructions using the components identified for that configuration.
The shipper is also responsible for determining that the selected packaging is authorized for the material being shipped and properly assembled for transportation. For more on how we document these details, see our compliance statements.
Which Traditional Pail Is Right for Your Product?
For qualifying hazardous solids, the M2 offers UN-certified solids configurations across a wide range of sizes. For qualifying hazardous liquids, the M4 offers specific UN-certified liquid configurations, with certain configurations also certified for solids.
Ultimately, the right choice depends on more than capacity. Your product, classification, required performance level, pail size, closure, and specific UN rating all play a role. You can also customize either pail with Offset or Heat Transfer printing so your regulated product still stands out.
Not sure which UN-rated configuration your product requires? We can help identify the appropriate pail and closure configuration for your application.
Contact us at 423-821-3302 or sales@mmcontainer.com
Frequently Asked Questions
What’s the main difference between the M2 and M4 pail?
The most visible difference is the closure. The M2 uses a grip-and-rip tear-tab lid, while the M4 uses a non-tear-tab, pressed-on cover. That closure difference is part of the tested UN configuration, which is why the two pails carry different certifications even though they share the same Traditional Pail family.
Is the M2 or M4 certified for hazardous liquids?
The M4 addresses hazardous liquids, with configurations carrying UN liquid ratings for Packaging Groups II and III. Certain M4 configurations also carry certifications for solids. The M2, by contrast, is certified for solids across its size range, so it’s important to match the specific pail and UN marking to your product.
What does the “S” mean in a UN marking?
An “S” at the end of a UN marking indicates the package has been tested for solids or inner packagings rather than as a single packaging for liquids. For a solids marking, the number before the “S” represents the maximum gross mass in kilograms. A liquid marking instead shows the maximum specific gravity and the applicable hydrostatic test pressure.
Can I switch the lid or fittings and keep the UN certification?
No. UN certification applies to the complete tested configuration, not just the pail body. If you switch lids, fittings, or other specified components, the original certification no longer applies. You must assemble the package using the components identified for that configuration and follow the applicable closure instructions.
How do I know which UN-rated pail my product needs?
Your choice depends on your product’s classification, the required performance level, the pail size, the closure, and the specific UN rating. The shipper is responsible for confirming that the packaging is authorized for the material being shipped. If you’re unsure, contact us and we’ll help identify the right pail and closure configuration for your application.
