The UN number identifies the dangerous goods material with a specific four-digit code, allowing everyone in the shipment chain to know exactly what substance is being transported. This consistent identifier is used across regulations so shippers, carriers, and emergency responders can recognize the material quickly and accurately. In practice, the UN number appears on shipping papers and on labels and placards, alongside the proper shipping name, hazard class, packing group, and quantity. This combination helps determine the appropriate handling, segregation, packing, and emergency response actions if there’s an incident. It doesn’t indicate packaging color or manufacture date, and it’s not optional for hazmat shipments—having the UN number is a required part of safe transport.

Absorbent materials are added to packaging to soak up liquids that escape from a container. They are designed to take in the leaked liquid, helping to contain spills, protect the product, and prevent environmental contamination. This is different from desiccants, which pull moisture from the air inside a package rather than absorbing a liquid leak. Cushioning protects against impact, not leaks, and tape's role is to seal rather than absorb. So the best choice is the absorbent.

Air hazmat transport follows a framework built specifically for aviation because airplanes pose different risks than ground or storage. The standard most carriers use worldwide is the IATA Dangerous Goods Regulations, which implement the ICAO Technical Instructions for the Safe Transport of Dangerous Goods by Air. The ICAO Technical Instructions set the baseline rules, and the IATA Dangerous Goods Regulations translate those rules into practical requirements for classification, packaging, labeling, documentation, handling, and training that shippers and airlines follow across borders. OSHA’s Hazard Communication Standard focuses on how chemicals are described and labeled in the workplace, not how they’re shipped. The U.S. regulations in 49 CFR Parts 171-180 cover hazmat rules for transportation in commerce, including some air movements, but they’re primarily a domestic framework and don’t replace the international air-specific guidance provided by IATA DGR and ICAO TI. NFPA 704 is a facility hazard-rating system, not a transport regulation.

Air transport imposes strict prohibitions on dangerous goods specifically for passenger aircraft because safety on board hundreds of people is the top priority. The IATA Dangerous Goods Regulations define what can be shipped on passenger aircraft and also cover shipments that combine passenger and cargo. Many dangerous goods are forbidden on passenger flights, and those that are allowed often must be shipped only on cargo aircraft or under highly controlled conditions with special packaging, labeling, and documentation. This framework—passenger aircraft shipments or combined passenger-cargo shipments under IATA DGR—is what enforces these prohibitions. Ground, rail, and sea have their own rules, but the restriction described here directly relates to air transport under the IATA DGR.