On the highway, the rules on which hazardous materials may share a truck are in the segregation table in 49 CFR 177.848(d). An "X" means the two classes may not be loaded, transported or stored together in the same vehicle at all; an "O" means they may only if separated so that a leak could not make them mix; a blank means no restriction. Explosives follow a second table of compatibility groups in 177.848(f), and a few pairs, such as cyanides with acids, are banned outright by 177.848(c).
This page explains how to read the table, reproduces it in plain form, and works through examples. Placarding, which is a different question, is on the placard requirements page.
First, the hazard classes
The segregation table is organised by class and division, so it helps to have the list from 173.2 in front of you.
| Class | Division | Name |
|---|---|---|
| 1 | 1.1 | Explosives with a mass explosion hazard |
| 1 | 1.2 | Explosives with a projection hazard |
| 1 | 1.3 | Explosives with predominately a fire hazard |
| 1 | 1.4 | Explosives with no significant blast hazard |
| 1 | 1.5 | Very insensitive explosives; blasting agents |
| 1 | 1.6 | Extremely insensitive detonating substances |
| 2 | 2.1 | Flammable gas |
| 2 | 2.2 | Non-flammable compressed gas |
| 2 | 2.3 | Poisonous gas |
| 3 | Flammable and combustible liquid | |
| 4 | 4.1 | Flammable solid |
| 4 | 4.2 | Spontaneously combustible material |
| 4 | 4.3 | Dangerous when wet material |
| 5 | 5.1 | Oxidizer |
| 5 | 5.2 | Organic peroxide |
| 6 | 6.1 | Poisonous materials |
| 6 | 6.2 | Infectious substance (etiologic agent) |
| 7 | Radioactive material | |
| 8 | Corrosive material | |
| 9 | Miscellaneous hazardous material |
Two practical notes. A combustible liquid is a liquid with a flash point above 60 °C (140 °F) and below 93 °C (200 °F) that meets no other class definition (173.120(b)(1)); a flammable liquid with a flash point at or above 38 °C (100 °F) may be reclassed as combustible (173.120(b)(2)). And the class of any named product, whether batteries or fireworks, comes from its entry in the 172.101 Hazardous Materials Table: for example, lithium ion batteries (UN3480) are Class 9, wet acid batteries (UN2794) are Class 8, and fireworks entries such as UN0336 are Division 1.4G.
When the segregation rules apply
177.848(a): the section applies to hazardous materials that are:
- in packages that must be labeled or placarded under Part 172;
- in a compartment of a multi-compartment cargo tank subject to 173.33; or
- in a portable tank loaded in a transport vehicle or freight container.
The trigger is labeling or placarding required for the package, not whether the truck itself is placarded. A load under the 1,001-pound placard threshold still has to be segregated if its packages must be labeled. When the vehicle is going onto a vessel other than a ferry, the vessel rules in 176.83(b) apply instead (177.848(b)).
How to read the symbols
177.848(e) defines each mark:
- Blank, or the class does not appear: no restriction (177.848(e)(1)).
- X: may not be loaded, transported or stored together in the same transport vehicle or storage facility during transportation (177.848(e)(2)).
- O: may not be loaded, transported or stored together unless separated so that, if packages leak under normal transport conditions, the materials would not commingle (177.848(e)(3)).
- *: segregation among different explosives is governed by the compatibility table in 177.848(f) (177.848(e)(4)).
- A: notwithstanding an X, ammonium nitrate (UN1942) and ammonium nitrate fertilizer may be loaded with Division 1.1 or 1.5 materials, unless 177.835(c) prohibits it (177.848(e)(5)).
The "O" rule has an extra sentence that matters for mixed freight: whatever separation is used, Class 8 liquids may not be loaded above or adjacent to Class 4 or Class 5 materials, except that shippers may load truckload shipments together when it is known the mixture would not cause fire or a dangerous evolution of heat or gas (177.848(e)(3)).
The table, row by row
The table in 177.848(d) is symmetrical: if 3 against 6.1 PG I Zone A is X, then 6.1 PG I Zone A against 3 is also X. Below, each class lists only the combinations the table restricts. Anything not listed is blank. Explosives against explosives follow the compatibility table further down.
| Class or division | May not be loaded together (X) | Only with separation (O) |
|---|---|---|
| 1.1 and 1.2 | 2.1, 2.2, 2.3 (both zones), 3, 4.1, 4.2, 4.3, 5.1, 5.2, 6.1 PG I Zone A, 7, 8 liquids (note A applies) | None |
| 1.3 | 2.1, 2.3 (both zones), 3, 4.2, 4.3, 5.1, 5.2, 6.1 PG I Zone A, 8 liquids | None |
| 1.4 | None | 2.1, 2.3 (both zones), 3, 4.2, 6.1 PG I Zone A, 8 liquids |
| 1.5 | Same as 1.1 and 1.2 (note A applies) | None |
| 1.6 | None outside Class 1 | None |
| 2.1 Flammable gas | 1.1, 1.2, 1.3, 1.5, 2.3 Zone A | 1.4, 2.3 Zone B, 6.1 PG I Zone A, 7 |
| 2.2 Non-flammable gas | 1.1, 1.2, 1.5 | None |
| 2.3 Poison gas, Zone A | 1.1, 1.2, 1.3, 1.5, 2.1, 3, 4.1, 4.2, 4.3, 5.1, 5.2, 8 liquids | 1.4 |
| 2.3 Poison gas, Zone B | 1.1, 1.2, 1.3, 1.5 | 1.4, 2.1, 3, 4.1, 4.2, 4.3, 5.1, 5.2, 8 liquids |
| 3 Flammable liquid | 1.1, 1.2, 1.3, 1.5, 2.3 Zone A, 6.1 PG I Zone A | 1.4, 2.3 Zone B, 5.1 |
| 4.1 Flammable solid | 1.1, 1.2, 1.5, 2.3 Zone A, 6.1 PG I Zone A | 2.3 Zone B, 8 liquids |
| 4.2 Spontaneously combustible | 1.1, 1.2, 1.3, 1.5, 2.3 Zone A, 6.1 PG I Zone A, 8 liquids | 1.4, 2.3 Zone B |
| 4.3 Dangerous when wet | 1.1, 1.2, 1.3, 1.5, 2.3 Zone A, 6.1 PG I Zone A | 2.3 Zone B, 8 liquids |
| 5.1 Oxidizer | 1.1, 1.2, 1.3, 1.5, 2.3 Zone A, 6.1 PG I Zone A (note A applies) | 2.3 Zone B, 3, 8 liquids |
| 5.2 Organic peroxide | 1.1, 1.2, 1.3, 1.5, 2.3 Zone A, 6.1 PG I Zone A | 2.3 Zone B, 8 liquids |
| 6.1 liquids PG I, Zone A | 1.1, 1.2, 1.3, 1.5, 3, 4.1, 4.2, 4.3, 5.1, 5.2, 8 liquids | 1.4, 2.1 |
| 7 Radioactive | 1.1, 1.2, 1.5 | 2.1 |
| 8 Corrosive liquids | 1.1, 1.2, 1.3, 1.5, 2.3 Zone A, 4.2, 6.1 PG I Zone A | 1.4, 2.3 Zone B, 4.1, 4.3, 5.1, 5.2 |
Read from 177.848(d). Two things the table does not contain. Division 2.2 against 2.3, and Class 9 and Division 6.2 against anything, have no entries, so the table imposes no restriction. And Division 6.1 appears only as "liquids PG I Zone A": other Division 6.1 materials are not restricted by this table, although the separate rules below still apply.
Poisons, food and the cab
177.841(e) adds limits that are not in the table:
- A package bearing or required to bear a POISON or POISON INHALATION HAZARD label or placard may not travel in the same vehicle as material marked as or known to be food, feed or other edible material, unless the poison is overpacked in a metal drum as specified in 173.25(c), or the poison and the food are each loaded in separate closed unit load devices (177.841(e)(1)).
- A Division 6.1 Packing Group III package (POISON label with "PG III") may travel with food only if separated so that leaks could not reach it (177.841(e)(3)).
- No package bearing or required to bear a POISON, POISON GAS or POISON INHALATION HAZARD label may be carried in the driver’s compartment, including the sleeper berth (177.841(e)(2)).
177.841(f) also allows one narrow exception to the table: toxic-by-inhalation hazardous waste of Division 6.1 PG I Zone A, carried by a private or contract carrier, may share a vehicle with Class 3, 4, 5 and 8 materials if palletised, packed as 173.226(c) requires, and separated by a buffer of at least 9 feet (2.74 m).
Three pairings banned outside the table
177.848(c), in addition to the table:
- Cyanides, cyanide mixtures or solutions may not be stored, loaded or transported with acids if mixing would generate hydrogen cyanide.
- Division 4.2 materials may not be stored, loaded or transported with Class 8 liquids.
- Division 6.1 PG I, Hazard Zone A material may not be stored, loaded or transported with Class 3, Class 8 liquids, or Divisions 4.1, 4.2, 4.3, 5.1 or 5.2.
Subsidiary hazards
177.848(e)(6): when a package must bear a subsidiary hazard label, segregation for the subsidiary hazard applies too, if it is more restrictive than the primary hazard’s. Materials of the same class may be stored together without regard to the subsidiary hazard if they cannot react dangerously with each other.
Explosives: the compatibility groups
Explosives carry a compatibility group letter after the division (1.4G, 1.1D). 177.848(f) says Class 1 materials may not be loaded, transported or stored together except as the compatibility table allows. The key readings from 177.848(g):
- X: explosives of those two groups may not be on the same vehicle.
- 1: group L only with an identical explosive.
- 2: any combination of groups C, D or E is treated as group E.
- 3: combinations of C, D or E with N are treated as group D.
- 4: see 177.835(g) when transporting detonators.
- 5: Division 1.4S fireworks may not be loaded with Division 1.1 or 1.2 materials.
- 6: group G articles, other than fireworks and those needing special handling, may go with C, D and E articles if no explosive substances are on the vehicle.
Group A cannot be carried with any other group, and groups B, F, H, J, K and L are incompatible with most others. Group S is the most permissive: it is compatible with most groups subject to notes 4 and 5, and not with A or L.
177.848(h): explosives of the same compatibility group but different divisions may travel together if the whole shipment is treated as the lowest division number; the rule’s example is 1.2D with 1.4D, transported as 1.2D. 177.848(i): 1.5D in the same freight container as 1.2D is treated as 1.1D.
Detonators have their own rule in 177.835(g): a detonator assembly or booster with detonator may not share a vehicle with Division 1.1, 1.2 or 1.3 material (other than other detonators of those types), detonating cord of Division 1.4, or Division 1.5 material, and detonators themselves need an MC 201 container or another packing method the rule allows. 177.835(c) also limits Division 1.1 and 1.2 in combinations: no more than two cargo-carrying vehicles, and no cargo tank that must be placarded in the combination, among other conditions.
Worked examples
Example 1. A van carries corrosive liquid (Class 8) and a flammable liquid (Class 3). The table cell is blank, so no segregation is required under 177.848(d). Normal load securement still applies.
Example 2. A driver is offered pool chemicals classed as oxidizer (5.1) and a drum of corrosive liquid (8). The cell is O, so they may travel together only if separated so that leaks could not mix, and under 177.848(e)(3) the corrosive liquid may not be loaded above or adjacent to the oxidizer. In practice this means floor loading at opposite ends of the trailer with blocking, or refusing the combination.
Example 3. A shipment includes a flammable gas cylinder (2.1) and a poison gas cylinder with Hazard Zone A (2.3). The cell is X: they may not be on the same truck.
Example 4. A spontaneously combustible material (4.2) and battery acid (Class 8 liquid) are offered together. The table shows X, and 177.848(c) bans the pair separately as well.
Tunnels and routes
Segregation decides what goes in the trailer; routing decides where the trailer goes. 397.67(b): a carrier with hazmat that must be placarded or marked under 177.823, and that is not subject to a state or tribal hazmat route designation, must use routes that avoid heavily populated areas, crowds, tunnels, narrow streets and alleys, unless there is no practicable alternative, a reasonable deviation is needed to reach a terminal, loading point, food, fuel, repairs, rest or a safe haven, or an emergency or law enforcement requires it. Operating convenience is not a reason (397.67(c)). Where a state or tribe has designated routes for non-radioactive hazmat, the carrier must follow them (397.67(a)). Many tunnel authorities post their own restrictions, and a state route designation can bar hazmat from a specific tunnel.
What inspectors check
- That classes on the shipping paper that are X against each other are not on the same vehicle.
- For O pairs, physical separation that would stop leaks commingling, and no Class 8 liquids above or next to Class 4 or 5 materials.
- For explosives, compatibility groups and, for 1.1 to 1.3 loads, the written route plan required by 397.67(d).
- That the driver has hazmat training covering segregation (providers are in the hazmat training directory, and the hazmat practice test covers the endorsement questions). The H endorsement knowledge test covers "cargo segregation" (383.121(b)(3)), and function-specific training is required of every hazmat employee (see HazMat employee training).