What 173.315P-HMGP means in plain language
When you haul hazardous materials in bulk, your cargo tank has internal stop valves—safety devices that prevent material from flowing out if a connection breaks or fails. These valves need to close automatically, and they need to do it reliably even under stress or temperature changes.
The regulation at 173.315P-HMGP requires that each of these internal self-closing stop valves must have a thermal means of closure. In plain terms: the valve must have a built-in mechanism (usually a fusible element or thermal-sensitive component) that forces it shut if it's exposed to excessive heat or fire. If your tank's internal stop valves lack this thermal protection, or if the existing thermal mechanism is damaged, missing, or non-functional, you can be cited.
This isn't about how you operate the valve day-to-day. It's about the mechanical integrity of the safety component itself—whether the valve hardware includes the right kind of redundant, heat-activated shutdown.
What our enforcement data actually shows
Across our 13 million+ inspection records, 173.315P-HMGP is extraordinarily rare. We have recorded only 2 citations all-time, with 1 in the last 90 days and 2 in the last 12 months. This ranks the code at #2651 of 3,036 FMCSR codes by citation volume.
More importantly for your situation: zero out of 2 citations ever resulted in an out-of-service placement. The OOS rate is 0.0%—significantly below the all-FMCSR average of 31.4%. That means inspectors who cite this violation typically see it as a repair-and-go situation, not a violation that grounds your truck at the scale.
The rarity and low enforcement severity suggest that inspectors encounter this defect infrequently, and when they do, the fix is usually straightforward enough that you can address it and continue your route.
Who gets cited most
In the last 180 days, our inspection database shows 1 citation in California. Both all-time citations (2 total) resulted in zero out-of-service placements across all states, so there is no meaningful OOS-rate variation to track.
Our data shows two carriers with a citation each: Paul Oil Company Inc (USDOT 423224) and Raghav Transportation Inc (USDOT 3846982). These are isolated citations—not patterns suggesting systemic non-compliance—and we see no repeated violations from either carrier in our records.
How severe is this compared to similar codes
Hazmat packaging and closure violations span a wide severity range in our inspection data. The peer codes in the Hazardous Materials category show striking contrasts:
177.834A-HMC (General loading/unloading hazmat) and 177.834(a) (also general loading/unloading) carry 3,954 and 3,839 citations respectively, with 99.2% and 97.9% out-of-service rates. These violations shut trucks down almost every time.
177.817(a) (Placarding violation) has 2,274 citations and a 75.1% OOS rate—serious, and often career-altering if it involves placarding omissions.
By contrast, 172.602(c)(1) (Maintenance/accessibility of Emergency Response information), a comparable hazmat compliance issue, has 1,464 citations and a 0.0% OOS rate—exactly matching 173.315P-HMGP's enforcement outcome.
Your citation sits in the low-enforcement, rarely-out-of-service category. The thermal closure mechanism is a safety redundancy rather than a primary operational requirement, and inspectors treat defects as fixable equipment issues.
How to avoid it
Know your tank's internals: Before taking on a hazmat load, confirm with the tank's maintenance records or the carrier dispatcher that all internal stop valves are equipped with thermal closure elements. If you're leasing or operating an unfamiliar tank, ask specifically about this feature—don't assume.
Inspect valve housings during pre-trip: Look for visible damage, cracks, or corrosion around the valve body and any exposed thermal elements (typically a fusible plug or thermal-sensitive cap). If you see rust, impact damage, or parts that look loose, flag it for maintenance. Don't haul a compromised tank.
Watch for heat damage after incidents: If your tank has been in any accident, near a fire, or exposed to extreme heat, have the thermal closure mechanisms inspected. The same accident that dents a valve housing may have damaged the thermal element inside. Our inspection data shows air-brake and chamber leaks sometimes co-occur with hazmat valve issues, suggesting that vibration and pressure stress can degrade seals and protective mechanisms over time.
Maintain separation from brake-related failures: Our records show two co-occurring citations: Air Brake valve leaks and audible air leaks from brake chambers appeared in the same inspections as thermal closure defects. Vibration from failing brake components can stress tank fittings. Keep your air brakes in good repair, and prioritize brake maintenance checks before or during routine tank inspections.
Document your pre-trip: Write down that you checked the valve closures and thermal mechanisms. If an inspector cites you, that documentation shows diligence. If a repair was needed and you had it done, keep the work order.
The bottom line: this violation is uncommon and usually not out-of-service. The fix is typically a replacement valve or thermal element, done by your carrier's maintenance team. Stay alert to thermal and valve-housing damage during pre-trip, and you'll avoid it.