What information does the four-digit UN identification number on a hazmat placard or orange panel provide?

THE UN (United Nations) IDENTIFICATION NUMBER system provides a globally standardized way to identify hazardous materials. Each number (UN 1203, UN 1090, etc.) identifies a specific chemical or class of chemicals. WHY IT MATTERS IN EMERGENCIES: A first responder at a crash scene cannot safely approach unknown hazmat cargo. By reading the UN number from a safe distance (binoculars if necessary) from the placard or orange panel, they can: look up the exact substance in the Emergency Response Guidebook (ERG); find the GUIDE NUMBER which tells them: recommended evacuation distances; fire-fighting methods; first aid procedures; personal protective equipment needed. ORANGE PANELS: In addition to or instead of placards, some vehicles carry orange panels (with UN number and hazard class number) on the front and rear — common in European-origin vehicles; PLACARD WITH UN NUMBER: Many hazmat placards display the 4-digit UN number in the center of the placard, providing both the hazard class (from the placard color and symbol) and the specific material identification (from the number). COMMON UN NUMBERS: UN 1203 — Gasoline; UN 1075 — Petroleum gases (LPG); UN 1090 — Acetone; UN 1993 — Flammable liquid (n.o.s.); UN 2794 — Lead acid batteries; UN 3373 — Biological substance Category B. DRIVER RESPONSIBILITY: Know where your shipping papers are (they provide UN numbers); know the UN numbers for the cargo you're carrying.