Some loads are dangerous not because of what they are made of, but because of how hot they are. A tanker of molten asphalt is not a fire or a poison in the usual sense; it is a burn hazard. The elevated temperature marking, the word HOT, exists to warn about exactly that.
This is study guidance, not regulatory advice. The binding rule is 49 CFR 172.325 and your official state CDL manual.
What it looks like and means
The marking is the word HOT, displayed inside a square set on point, like a diamond. It tells handlers and responders that the material is being transported at a temperature high enough to injure on contact, so the load must be approached with that in mind.
| Feature | Elevated temperature marking |
|---|---|
| Text | HOT |
| Shape | Square set on point |
| Class number | None (it is a marking) |
| Signals | The material is dangerously hot |
The temperature thresholds
A material is generally treated as an elevated temperature material when it is, in transport, a liquid at or above about 212 degrees F (100 C) or certain solids at or above about 464 degrees F (240 C). Molten sulfur and molten asphalt are the classic examples. Many elevated temperature materials also fall under Class 9.
Why it is a marking, not a placard
Like the marine pollutant marking and the limited quantity marking, the HOT marking is a marking rather than a hazard-class placard. It carries no class number and does not replace a required placard; it adds information. Recognizing the difference between markings and placards is the same skill behind knowing that placards and labels follow different rules.
Where it fits
For the federal framework, see the FMCSA hazardous materials regulations and the PHMSA hazmat resources. For the test, the takeaway is direct: HOT means an elevated temperature material, and it is a marking that sits alongside any hazard placards the load requires.
Frequently asked questions
What does the HOT marking on a truck mean?
It is the elevated temperature marking. It warns that the material is being transported at a temperature high enough to cause burns, such as molten sulfur or molten asphalt.
What temperature requires the HOT marking?
Generally a liquid at or above about 212 degrees F (100 C) in transport, or certain solids at or above about 464 degrees F (240 C). Confirm the exact thresholds in the regulation.
Is the HOT marking a hazard placard?
No. It is a marking about temperature, not a hazard-class placard. It has no class number and does not replace a required placard.
What is the best way to study hazmat markings?
Practice telling markings apart from hazard placards with a recognition app such as CDL Placards, and confirm the thresholds and rules in your state CDL manual, which is the source of truth.
