Under federal placarding rules, what are the size and visibility requirements for a hazmat placard displayed on a vehicle?

49 CFR 172.504(a) (placement of placards on the front, rear, and both sides of the vehicle) and 172.519(c)(1) (minimum placard size of 250 mm / 9.84 in per side); 172.516 governs visibility from the direction a placard faces but is not the source of the f

Placards are the first thing emergency responders look for after a crash to know what hazards they're dealing with before opening a trailer. A placard that's too small, faded, or placed where it can't be seen from one of the four approach directions can delay the correct emergency response and put first responders at risk.