Your fire extinguisher is correctly rated at 10 B:C, but it's stored loose on top of a pallet of cargo behind locked trailer doors, because there's no mounting bracket up front in the cab. Does this setup meet the federal requirement?

49 CFR 393.95(a)(4)

An extinguisher that's rated correctly but buried under cargo or rolling loose in the back is useless in the first critical seconds of a fire. Federal rules require it to be mounted securely and placed where the driver can reach it immediately, because a fire that reaches a hazmat load can escalate from manageable to catastrophic in under a minute. Inspectors check both the rating and the mounting/accessibility during roadside inspections.