What 178.338-8 means in plain language
FMCSR 178.338-8 covers the pressure relief devices required on MC338 cargo tanks—the specialized trailers used to transport cryogenic liquids and other hazardous materials under pressure. These devices are critical safety components that prevent tank overpressurization and catastrophic failure during transport.
The regulation requires that pressure relief devices on MC338 tanks meet specific design, installation, and operational standards. A citation for this code typically means an inspector found a pressure relief device that was missing, damaged, improperly installed, not functioning as designed, or otherwise failed to meet DOT specifications. This could include relief valves that won't open at the correct pressure, damaged or corroded devices, or devices installed in the wrong location on the tank.
Because these devices are safety-critical on tanks carrying hazardous materials under extreme conditions, maintaining them in proper working order is non-negotiable.
What our enforcement data actually shows
Across our 13 million+ roadside inspection records, 178.338-8 citations are exceptionally rare. We have recorded only 2 citations all-time for this code, with both occurring within the last 12 months—one in June 2025 and one in September 2025. Over the last 90 days, we have seen zero citations.
None of the 2 citations on record resulted in an out-of-service order, giving this code a 0.0% OOS rate. This stands in sharp contrast to the all-FMCSR average OOS rate of 31.4%, meaning inspectors and carriers treat pressure relief device violations very differently than typical roadside findings. The extremely low citation volume and zero OOS rate suggest either exceptional compliance in this area or very selective enforcement tied to specific inspection protocols for MC338 carriers.
Nationally, 178.338-8 ranks #2651 out of 3,036 FMCSR codes by total citation volume, placing it among the rarest violations in the roadside inspection database.
Who gets cited most
Our inspection records show only two carriers with citations for this code all-time. TEAMONE LOGISTICS LLC (USDOT 2525242) and CRYOGENICS FREIGHT LLC (USDOT 3916810) each appear once in our data. Both citations resulted in warning-level citations rather than out-of-service orders, reflecting the rare and specific nature of pressure relief device findings.
Because the total citation count is so low, we cannot reliably identify state-level hotspots or patterns across geographies. The scarcity of citations suggests that either MC338 pressure relief devices are in near-universal compliance, or that routine roadside inspections rarely focus on this particular component unless a carrier operates an MC338 tank and an inspector specifically audits those systems.
How severe is this compared to similar codes
Within the Hazardous Materials category, pressure relief device violations are dramatically less common than other hazmat-related inspection findings. For comparison:
- 177.834A-HMC (General loading/unloading hazmat) has 3,954 citations with a 99.2% OOS rate—one of the highest-impact hazmat violations.
- 177.817(a) (Placarding violation) has 2,274 citations with a 75.1% OOS rate.
- 172.602(c)(1) (Maintenance/accessibility of Emergency Response information) has 1,464 citations with a 0.0% OOS rate, matching this code's OOS rate but with vastly higher enforcement volume.
The stark difference between 178.338-8's 2 all-time citations and the thousands of citations for general hazmat loading, placarding, and documentation violations suggests that pressure relief device inspections occur under narrower circumstances—likely only when an MC338-specific inspection is conducted or when a tank is opened for service.
How to avoid it
Because citations for this code are rare and you almost certainly operate a standard dry van, flatbed, or standard reefer trailer, direct risk is low. However, if you ever transition to hauling cryogenic liquids or other pressurized hazmat on an MC338 tank, these actions will protect you:
- Pre-trip walk-around. Physically inspect the pressure relief valve assembly on the tank before every load. Look for visible damage, corrosion, or loose components. Verify the device is mounted securely in its designated location.
- Know your tank's specifications. Obtain and carry documentation showing the correct pressure setting for your tank's relief device. Confirm with your dispatcher that you understand the rated opening pressure and have confirmation from the shipper or tank service provider that the device is calibrated correctly.
- Never operate with a suspect device. If you notice a relief valve that appears damaged, cracked, or corroded, report it to your fleet maintenance immediately and do not transport pressurized cargo until it is replaced or certified by a qualified technician.
- Schedule regular maintenance. Pressure relief devices must be inspected and tested at DOT-required intervals. Ensure your company's maintenance schedule includes periodic recalibration of relief valves per manufacturer specs.
- Document all service. Keep copies of all relief device inspections, tests, and replacements in your vehicle file. Inspectors may ask for this documentation if they conduct a detailed MC338 audit.
If you drive standard freight and never handle MC338 tanks, this code is not a realistic citation risk. Focus your compliance efforts on the violations you are more likely to encounter during pre-trip and roadside inspection.