You can’t just load a truck and send it off down the highway without knowing the nature of the hazardous materials (hazmats) that will be transported together. You need to confirm that the hazmats you’re loading on a motor vehicle, transporting by highway, or storing are compatible.

Segregate before shipping

The Department of Transportation (DOT) specifies combinations of hazmats that can only be transported together if they are separated in a way that would not allow the commingling of the materials in the event packages leak during normal transportation conditions. The DOT also forbids, under any conditions, the transportation of certain combinations of hazardous materials because of their potential to pose serious hazards. However, the DOT does allow some hazmats to be transported or stored together on the basis of its determination that incompatible chemical reactions would not occur. The idea is to prevent the risk of explosions, fires, creation of toxic gas, and the like that might occur if the materials commingle. The key to figuring out which materials can or cannot be loaded, transported, or stored together is the DOT Segregation Table for Hazardous Materials (Table). So let’s go over how to use the Table so that you’re aware of the restrictions that limit or prevent consolidation of hazmats with different hazard classes or divisions in a single highway shipment.

How the Table works

First of all, the Table only applies to packages that must be labeled or placarded. The Table is used to compare two materials at a time, based on their hazard class or division. On the far left Column, headed “Class or Division,” you must look down the row until you find the class or division for the first material you plan to ship. Then, at the top of the Table, look from left to right for the class or division of the second material you will ship. Once you find that second material’s class or division, go down that column until you find where it intersects with the row you’ve chosen in the far left column. At that intersection will be a symbol that indicates the restriction applicable to transporting or storing these two materials together. A hazard class or division that’s not on listed on the table is not restricted. For example, there’s no “Class 9” on the table. That means that the segregation rules do not apply to Class 9 hazmats.

As an example, locate “flammable liquids” in the far left column. The number following this name, “3,” indicates that it is hazard class 3. Follow the column at the top of the table to Class 4.2, the hazard class of our example’s second material (spontaneously combustible materials). Where they intersect, there is a blank space. To understand what that signifies, you need to look at the Table’s instructions, which explain the symbols. This version of the Table illustrates the example and other information we’ll discuss in connection with this example.)

Symbols on the Table

The symbols used in the Table and their meaning are explained in the Table’s instructions:

• As with our example, if there is no symbol where the two hazmats intersect, that means that these hazmats can be transported or stored together and that no segregation restrictions apply.
• An “X” at the intersection means that the materials may not be loaded, transported, or stored together in the same transport vehicle or storage facility during the course of transportation.
• An “O” at the intersection means that these materials may be loaded, transported, or stored together in the same transport vehicle or storage facility during the course of transportation but only if they are separated in a manner that, in the event that both packages leak during normal transportation conditions, the hazardous materials would not commingle. (Separation requirements can be met with barriers such as impediments, obstructions, dividers, packages of non-hazardous materials, or intervening space between packages inside of the transport vehicle that prevent commingling of materials in the event the packages leak.)
• A “*” (star) indicates that segregation among different Class 1 materials (explosives) is governed by the special compatibility table for Class 1 Explosive Materials found at 49 CFR 177.848(f). That table should be consulted if more than one Class 1 explosive is being transported together.
• An “A” in the notes column indicates that even if there’s an “X,” ammonium nitrate (UN1942) and ammonium nitrate fertilizer may be loaded or stored with Division 1.1 or Divisions 1.5 materials unless otherwise prohibited at 49 CFR 177.835(c).

Consider all the hazards

So, to go back to our example, the blank space on the Table where our two hazmats intersect shows that the two hazards can be transported together—but we can’t just stop there and load these hazmats onto the truck. It’s important to know that subsidiary hazards must be considered.

If Column 6 of the 49 CFR 172.101 table (aka the Hazardous Materials Table) or 49 CFR 172.402 (additional labeling requirements) specify that either hazmat package must bear a subsidiary hazard label, then segregation appropriate to the subsidiary hazard must be followed when that segregation is more restrictive than the segregation required by the primary hazard.

Let’s say our particular flammable liquid with hazard class 3, which is its primary hazard, has a second hazard, Class 8 (corrosive liquids). We would also have to check the intersection of hazard Class 8 with that of our second hazmat, which has hazard Class 4.2. Because there’s an “X” at the intersection of Class 8 and Class 4.2, the two hazmats of our example cannot be transported together by highway.

However, DOT does allow hazardous materials of the same class to be stowed together without regard to segregation required for any secondary hazard if the materials are not capable of reacting dangerously with each other and causing combustion or dangerous evolution of heat, evolution of flammable, poisonous, or asphyxiant gases, or formation of corrosive or unstable materials.

The take away

Your familiarity with the DOT Segregation Table for Hazardous Materials will help you ensure that you’re safely transporting your hazmats and avoiding accidents as well as the penalties associated with violating the hazmat segregation requirements.