# Los Alamos National Laboratory — Hazardous Materials Safety Interpretation

**Citation:** 08-0049  
**Type / status:** guidance / guidance  
**Agency:** Pipeline and Hazardous Materials Safety Administration  
**Effective:** Not stated  
**Published:** 2008-03-18

08-0049 response to Los Alamos National Laboratory concerning 172.504, 172.522.

## Document text

<<<PAGE 1>>>

1200 New Jersey Avenue, SE
vrue+h$on, D.C. 20590
U.S. Department
of Transportation
Pipeline and Hazardous
Materials Safety
Administration
MAR 1 8 259
Ms. Lorelei Johnson
Transportation Specialist
Weapons Engineering Technology (WT-DO)
High Explosives Engineering (WT-5)
Los Alamos National Laboratory
P.O. Box 1663, Mail Stop C932
Los Alamos, NM 87545
Reference No. 08-0049
Dear Ms. Johnson:
This is in response to your January 22,2008 letter asking if a Class 1 (explosive)
compatibility group letter must be displayed on an EXPLOSIVE placard when the material is
transported by motor vehicle under the Hazardous Materials Regulations (HMR; 49 CFR
Parts 171- 180). You note that 5 172.522(b) requires the compatibility group letter for the
Division 1. I, 1 -2, or 1.3 (explosives) placard, but 5 172.504(g) does not address transportation
by motor vehicle.
The answer is no. Section 172.504(g) requires the display of the compatibility group letter on
placards or labels, if appropriate (see 5 172.4 1 l), for shipments of Class 1 material transported
by aircraft or vessel only. If more than one compatibility group placard is required,
5 172.504(g) requires only one of these placards to be displayed provided this placard
conforms with the precedence requirements prescribed in paragraphs (g)(l) through (g)(4) of
that section. Although the HMR does not require the compatibility group letter for motor
vehicle and railcar shipments of Class 1 material, please note that § 172.502(c) permits it to be
displayed provided the placards otherwise conform to the requirements prescribed in 49 CFR
Part 172, Subpart F (placarding). Section 172.401(a)(2) also permits a hazard warning label
to be displayed provided the label represents the hazard class of the material in the package.
I hope this satisfies your request.
H'attie L. Mitchell
Chic$ Regulatory Review and Reinvention
Office of Hazardous Materials Standards

<<<PAGE 2>>>

I
1 NATIONAL Alamos LABORATORY
EST.1943 - F'Bu'm
Weapons Engineering Technology (WT-DO)
High Explosives Engineering (WT-5)
P.O. Box 1663, Mail Stop C932
Los Alarnos, New Mexico 87545 Date: January 22, 2008
505-667-6563lFax 505-665-0467 Rehr TO: VVT-5-08:0005
Mr. Edward Mauullo
Director of the Office of Hazardous Materials Standards
U.S. DOTP HMSA (PHH-10)
1200 New Jersey Avenue
SE Building 2"d Floor
Washington, DC 20596
Sir,
I have a question concerning displaying the compatibility group letter on explosive placards.
172.522 (b) "The shall be replaced with the appropriate division number and, when required,
appropriate compatibility group letter." My question is: Is the compatibility group letter required for
highway transportation? 172.504 (g) does not address highway transportation.
Thank you,
Lorelei Johnson, WT-5, C932
Transportation Specialist
c y :
WT-5 File

## Provenance

- Official: Yes
- Source: <https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/2008/080049.pdf>
- Source ID: `phmsa`
- SHA-256: `f08a1085bccc9dbb7c7ff1f3c65c0ff334d4b1c1788fd2426a08c35350415c3c`
- Retrieved: 2026-08-20T00:59:31.977Z
- Exported: 2026-08-22T14:24:48.090Z
- Document slug: `phmsa-interpretation-08-0049`

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