Which of the following correctly states the no-smoking distance and the hazard classes covered under the hazmat driving and parking smoking prohibition?

49 CFR 397.13; AAMVA CDL Manual Sec 9.6.6 (nhcdm.pdf p.9-14)

Flammable vapors from Class 3 liquids and flammable solids are often invisible and can be heavier than air, meaning they can collect near the ground well outside what looks like the danger zone. A lit cigarette 20 feet away can still ignite vapors you can't see or smell, so the 25-foot line provides a real safety margin rather than an arbitrary number.