If you sell beauty products, consumer electronics, automotive supplies, or household goods, you're probably shipping hazardous materials. Aerosols, lithium batteries, nail polish, perfume, spray paint, pool chemicals. All regulated. All with specific rules about what can and can't share a box.
This article breaks down the segregation requirements that apply when packing orders with multiple hazmat items. It's not comprehensive (the full regulations run hundreds of pages), but it covers what most e-commerce operators actually need to know.
Before getting into what can ship together, you need to know how materials are classified. The DOT uses nine hazard classes:
Class 1: Explosives Fireworks, ammunition, airbag inflators. Most e-commerce operations won't touch these.
Class 2: Gases Aerosols fall here. Hairspray, spray deodorant, spray paint, compressed air dusters. If it's pressurized and can spray, it's probably Class 2. This class has three divisions:
Class 3: Flammable Liquids Perfume (UN1266), nail polish (often UN1263), essential oils, hand sanitizer, paint, adhesives, fuel. Anything with a flash point below 100°F (38°C) in most cases.
Class 4: Flammable Solids Matches, certain batteries, oily rags. Less common in typical e-commerce.
Class 5: Oxidizers and Organic Peroxides Pool chemicals, hair dye with peroxide, some bleaches. These make other things burn more intensely.
Class 6: Toxic and Infectious Substances Pesticides, certain cleaning concentrates, medical specimens.
Class 7: Radioactive Smoke detectors technically qualify, though they're usually exempt.
Class 8: Corrosives Drain cleaner, battery acid, some rust removers. Acids and bases that destroy tissue or metal.
Class 9: Miscellaneous Lithium batteries (UN3481 for lithium ion packed with equipment, UN3480 for lithium ion shipped alone), dry ice, magnetized materials. The catch-all category.
The segregation requirements live in 49 CFR 177.848. The regulation includes a table that shows which classes can and cannot be loaded together.
The table uses three codes:
X means do not load, transport, or store together. Period.
O means you can load them together only if they're separated in a way that prevents the materials from mixing if packages leak. In practice, for parcel shipping, this often means separate boxes.
Blank means no restriction between those classes.
Here are the key conflicts:
| Conflict | Why |
|---|---|
| Class 3 (flammable liquids) + Class 5.1 (oxidizers) | Oxidizers make flammables burn faster and hotter |
| Class 8 (corrosives) + Class 4 (flammable solids) | Corrosive liquids can ignite flammable solids |
| Class 8 (corrosives) + Class 5 (oxidizers) | Can create violent reactions |
| Class 2.1 (flammable gas) + Class 5.1 (oxidizers) | Same issue as Class 3 |
| Division 4.2 (spontaneously combustible) + Class 8 liquids | Fire risk |
| Cyanides + Acids | Generates hydrogen cyanide gas |
Here's where it gets practical. Some common order combinations that create problems:
Beauty subscription box:
Same box, add pool sanitizer:
Home improvement order:
Electronics with cleaning supplies:
Some products have more than one hazard. A corrosive that's also flammable, for example. The regulations say you must apply whichever segregation rule is more restrictive.
Aerosols are a good example. UN1950 covers multiple variants:
If you're shipping an aerosol with a corrosive subsidiary hazard, you need to apply both the Class 2 restrictions AND the Class 8 restrictions.
Everything above applies to ground transport (49 CFR). Air transport adds another layer: IATA Dangerous Goods Regulations.
IATA is generally stricter. Some materials that can ship together by ground are forbidden to ship together by air. Some materials are forbidden on passenger aircraft entirely and can only go on cargo aircraft.
If your fulfillment operation ships via FedEx, UPS, or USPS and uses air routes, you need to check both sets of requirements.
Key IATA differences:
There's some good news. Small quantities of many hazmat items can ship under "limited quantity" provisions with reduced requirements.
For ground transport (49 CFR), limited quantity shipments are exempt from:
The quantity limits vary by material. For Class 3 (flammable liquids) in Packing Group II, for example, inner containers can't exceed 1 liter and the outer package can't exceed 30 kg gross weight.
Limited quantity does not exempt you from segregation requirements. If two materials can't ship together in full quantities, they still can't ship together in limited quantities.
Every regulated hazmat has a UN number. You need this to determine the hazard class and applicable rules.
Where to find it:
Common e-commerce UN numbers:
We built hazmat segregation directly into the packing optimizer. Add a UN number to your item data, and StoaPack automatically looks up the hazard class, checks compatibility against other items in the order, and assigns incompatible materials to separate packages. It also applies packing group restrictions and flags items that can't ship by air.
No manual lookup. No hoping someone catches the conflict at the pack station.
Full API documentation is at stoapack.stoalogistics.com/api/docs.
49 CFR 177.848: The actual segregation regulation ecfr.gov/current/title-49/section-177.848
DOT Hazardous Materials Table: Lists all regulated materials with UN numbers, classes, and packing requirements ecfr.gov/current/title-49/section-172.101
PHMSA Hazmat Info Center: 1-800-467-4922
IATA DGR: For air transport requirements (updated annually, requires purchase) iata.org/publications/dgr