FMCSR 178.337-9C: MC331 Marking — Driver Q&A

No. Across our 13 million inspection records, this violation has never resulted in an out-of-service order—0.0% OOS rate. All 3 all-time citations were issued with the truck remaining in-service. This is significantly more lenient than the national average OOS rate of 31.4% across all FMCSR codes. However, it's still a hazmat violation and should be corrected immediately.

178.337-9C is one of the least-enforced hazmat infractions in our database. It ranks #2551 out of 3,036 FMCSR codes by citation volume, with only 3 all-time citations. By contrast, peer violations like general loading/unloading hazmat infractions (177.834A-HMC) have been cited 3,954 times with a 99.2% OOS rate, and placarding violations (177.817(a)) show 2,274 citations with 75.1% OOS rates. Your citation is rare and carries lower enforcement intensity.

1. Document the violation. Note the inspection date, location, and inspector ID.
2. Verify the marking. Review your MC331 tank inlet and outlet markings against current DOT hazmat regulations.
3. Correct any defects. If markings are missing, faded, or incorrect, repair or repaint them immediately.
4. Request re-inspection (if available in your state) to clear the citation.
5. Report to your carrier/safety manager. Even though it won't trigger an OOS order, hazmat violations must be documented for compliance records.

Our inspection records show only 3 all-time citations for this code across all states. Because enforcement is so sparse, there is no clear geographic hotspot. The carriers cited were California Gas Transport Inc, High Pressure Transports LLC, and Impetus LLC—each with a single citation. This suggests the violation is caught opportunistically during general hazmat inspections rather than through targeted enforcement campaigns.

While not immediately out-of-service, hazmat marking violations must be corrected promptly. Our data shows zero citations in the last 90 days and zero in the last 12 months, indicating very low current enforcement frequency. However, marking inlets and outlets on MC331 tanks is a DOT safety requirement—operating a tank with defective or missing markings exposes you to liability and future citations. Repair within 7–14 days to stay compliant.

Yes. If you believe the citation was issued in error—for example, the markings were actually compliant or the inspector misidentified your vehicle—you can contest it through FMCSA's DataQs (Dataqualification System). Provide photographs of the markings from the inspection date and any maintenance records. Equipment-condition disputes are often successful if you can show documentation that markings met standards at the time of inspection.

Hazmat violations are recorded against the motor carrier (your company's USDOT number), not the individual driver. The citation will appear on your carrier's Safety Management System profile and may affect their hazmat CSA scores. However, the violation does not transfer if you change employers. Your responsibility is to report it to your current safety manager and ensure the equipment is corrected before your next hazmat load.