What is an NA number and how does it differ from a UN number?

An NA number (North America number) is issued by the United States Department of Transportation for substances regulated under US domestic hazmat rules that do not have an assigned UN number. NA numbers use the range NA 9000 to NA 9279. Most NA numbers are identical to their UN equivalents for the same substance, but some NA entries cover goods or configurations not recognised in the international UN system — NA 3334 covers self-defence spray (non-pressurised) while UN 3334 covers aviation-regulated liquid, not otherwise specified. NA numbers are not used in European ADR transport documentation. All dangerous goods consignments on European roads use UN numbers from the Orange Book, regardless of whether the goods also carry an NA designation for US domestic transport.