Hazmat Segregation for E-commerce: What Can Actually Ship Together

Editor’s note (October 30, 2026): We checked this post against the federal regulations and rewrote the parts that were wrong. The original version treated the highway segregation table (49 CFR 177.848) as a rule about what can share a box. That table governs which packages can be loaded together in a vehicle; what goes inside one box is a separate rule. We also corrected the examples, the air and carrier section, the Class 3 flash point, several UN number descriptions, and the limited quantity section.

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.

“What can ship together” is really two questions, and the regulations answer them separately:

What can share one box? Covered by 49 CFR 173.21(e) and 173.24a(c).
Which packages can ride next to each other in a truck or plane? Covered by the segregation tables: 49 CFR 177.848 for highway, 175.78 for aircraft.

This article covers both. It’s not comprehensive (the full regulations run hundreds of pages), but it covers what most e-commerce operators actually need to know.

The Nine Hazard Classes

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:

2.1: Flammable gas (most aerosols)
2.2: Non-flammable, non-toxic gas
2.3: Toxic gas

Class 3: Flammable Liquids - Perfume (UN1266), nail polish (often UN1263), essential oils, hand sanitizer, paint, adhesives, fuel. Class 3 covers liquids with a flash point of 140°F (60°C) or lower. For domestic ground only, a liquid that flashes at 100°F (38°C) or higher can be reclassed as a combustible liquid.

Class 4: Flammable Solids, Spontaneously Combustible, and Dangerous When Wet Materials - Matches, sodium batteries, oily rags (regulated only by air and water). 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 contained in or packed with equipment, UN3480 for lithium ion shipped alone), dry ice, and, for air shipments, strongly magnetized materials. The catch-all category.

Federal rules forbid putting a material “in the same packaging, freight container, or overpack with another material, the mixing of which is likely to cause a dangerous evolution of heat, or flammable or poisonous gases or vapors, or to produce corrosive materials” (49 CFR 173.21(e)). That’s a chemistry question, not a table lookup: each product’s safety data sheet lists incompatible materials in Section 10 (Stability and reactivity), so compare the SDSs of the products you want to pack together.

When one box holds more than one hazardous material, 173.24a(c) adds conditions. Each material’s inner and outer packaging must meet its own packaging rules, and corrosive materials in bottles must be packed in securely closed inner receptacles first. By air, the total in one box can’t exceed the lowest per-package limit of the materials inside.

Rule 2: Which packages can ride together

The highway segregation table lives in 49 CFR 177.848. It governs which packages can be loaded together in a vehicle, not what goes inside one box, and it applies to packages that must carry hazard labels or placards.

The table uses three codes:

X means do not load, transport, or store together in the same vehicle or storage facility. Period.
O means they can’t be loaded together unless they’re separated so that, if a package leaks, the materials can’t mix. In practice, this is the carrier’s loading problem: the packages have to be placed in the vehicle so a leak from one can’t reach the other.
Blank means no restriction between those classes.

Real Examples for E-commerce

Here’s where it gets practical:

Beauty subscription box:

Aerosol dry shampoo (Class 2.1, UN1950)
Nail polish (Class 3, UN1263)
No restriction between Division 2.1 and Class 3 in the segregation table. Whether they share a box comes down to Rule 1: check the SDS.

Same box, add pool sanitizer:

Aerosol dry shampoo (Class 2.1)
Pool chlorine tablets (Class 5.1 oxidizer)
Neither the highway nor the air segregation table separates Division 2.1 from Division 5.1. Inside one box, though, 173.21(e) forbids combining materials that could react dangerously, and pool oxidizers react with many common products, so check the SDS and give the chlorine its own box.

Home improvement order:

Spray paint (Class 2.1, UN1950)
Drain cleaner (Class 8 corrosive)
Paint thinner (Class 3)
The highway table puts no restriction between Class 8 and Class 3 or Division 2.1. Its “not above or adjacent” rule for corrosive liquids covers only Class 4 and Class 5 materials. Inside one box, 173.24a(c) still requires corrosive bottles to be sealed in an extra inner receptacle, and Rule 1 still applies.

Electronics with cleaning supplies:

Laptop with lithium battery (Class 9, UN3481)
Aerosol screen cleaner (Class 2.1 or 2.2 depending on formulation)
Class 9 has no segregation restrictions with other classes in the 177.848 table. Neither table restricts this pair; they can share a box as long as Rule 1 is met, though lithium batteries have their own packaging requirements. See our guide to shipping lithium batteries.

Subsidiary Hazards

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 entries in the US Hazardous Materials Table, including:

Aerosols, flammable (2.1)
Aerosols, non-flammable (2.2)
Aerosols, corrosive (2.2 with Class 8 subsidiary)
Aerosols, poison (2.2 with Class 6.1 subsidiary)

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.

Air vs. Ground

The 177.848 table above is the highway rule. Air shipments follow a separate segregation table in 49 CFR 175.78, and air carriers also apply the IATA Dangerous Goods Regulations.

Air is generally stricter. Some materials are forbidden on passenger aircraft entirely and can only go on cargo aircraft, and some can’t fly at all.

FedEx requires IATA rules for air shipments, and UPS accepts either DOT or IATA rules for air within the US, so check both. USPS doesn’t fly flammable gases, liquids, or solids at all.

Key air differences:

Quantity limits are usually lower
Some products are forbidden on aircraft entirely; poison aerosols (UN1950, 2.2 with a 6.1 subsidiary) can’t fly at all under 49 CFR
Flammable liquids and oxidizers that only need separation on a truck can’t be stowed next to each other on an aircraft
Lithium battery requirements are more restrictive

Limited Quantity Exceptions

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 excepted from:

Shipping papers (unless the material is a hazardous substance, hazardous waste, or marine pollutant)
Placards
Hazard labels (though you still need the limited quantity mark)

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.

By ground, limited quantity packages need no hazard labels or placards, so the 177.848 vehicle table doesn’t apply to them. The in-box rule still does: never pack materials together that could react dangerously. By air, limited quantity packages are labeled and the air segregation rules apply. The full rules are in our Limited Quantity shipping guide.

Finding the UN Number for Your Products

Almost every regulated hazmat has an identification number, usually a UN number (a few US-only entries use NA numbers). You need it to determine the hazard class and applicable rules.

Where to find it:

Safety Data Sheet (SDS): Section 14 usually contains transport information including the UN number, proper shipping name, hazard class, and packing group
Manufacturer: If the SDS doesn’t have it, ask
Product label: Sometimes printed directly on consumer products

Common e-commerce UN numbers:

UN1950: Aerosols (covers many formulations)
UN1266: Perfumery products
UN1263: Paint (including nail polish)
UN1170: Ethanol / ethyl alcohol (hand sanitizer)
UN3481: Lithium ion batteries contained in or packed with equipment
UN3480: Lithium ion batteries shipped alone
UN3090: Lithium metal batteries shipped alone (UN3091 when contained in or packed with equipment)
UN1791: Hypochlorite solution (bleach)
UN1760: Corrosive liquid, n.o.s.

How StoaPack Handles This

We built hazmat handling directly into the packing optimizer. Add a UN number and the net quantity per unit to your item data, and StoaPack looks up the hazard class for supported UN numbers and packs each dangerous-goods item type in its own box, away from non-hazmat items. That is more conservative than the regulations require: even two materials that may legally share a box, like the dry shampoo and nail polish above, go in separate boxes. Supported package quantity limits are checked too, and unknown UN numbers on ground shipments are kept isolated with a warning.

For air or sea, StoaPack only accepts requests it has coverage for: it rejects unsupported requests outright, and lithium batteries by air are not supported.

Fewer manual lookups: StoaPack separates dangerous goods into their own boxes before the order reaches the pack station. Its hazmat checks are decision support, though, not shipment certification: they don’t replace your hazmat training, shipping papers, or a compliance review.

Resources

49 CFR 173.21: Forbidden materials and packages, including mixing materials that could react dangerously in one package
49 CFR 173.24a: Additional requirements for non-bulk packages, including mixed contents
49 CFR 177.848: The highway segregation table
49 CFR 175.78: The aircraft segregation table
DOT Hazardous Materials Table: Lists all regulated materials with UN numbers, classes, and packing requirements
PHMSA Hazmat Info Center: 1-800-467-4922
IATA DGR: For air transport requirements (updated annually, requires purchase)