What type of items can fall under Hazard Class 9?

Hazard Class 9 is designated for miscellaneous dangerous goods that present a hazard during transport but do not fall under other specific hazard classes. This class includes items that might not fit neatly into categories of flammability, health risks, or environmental hazards.

Airbag inflators are categorized under Hazard Class 9 because they contain substances that can pose a risk during transportation, but do not meet the criteria for the other more specific hazardous materials classes. They can be considered dangerous as they contain chemical agents that function under pressure, and the potential for an unintended activation during handling adds to their risk profile.

The other items listed, such as polyethylene or hydrochloric acid, fall under more specific hazard classes. Polyethylene is generally considered a non-hazardous material, and hydrochloric acid is classified as a hazardous material due to its corrosive properties. Uranium, depending on its form and concentration, typically falls under Class 7 for radioactive materials. Thus, airbag inflators are the correct choice for items classified under Hazard Class 9.