Which hazard class typically includes materials that are not ignitable?

The correct choice identifies Hazard Class 2, which encompasses gases, including compressed gases, liquefied gases, and those that may be toxic or inert. While some gases in this category can indeed be flammable, many are not ignitable, particularly if they are classified as non-flammable or non-combustible. This class addresses substances that may pose different types of hazards but do not primarily require ignition to cause harm.

Conversely, Hazard Class 1 pertains to explosives, which are designed to be reactive and have the potential to ignite under certain conditions. Hazard Class 3 covers flammable liquids that are inherently ignitable. Hazard Class 4 includes flammable solids, reactive solids, or substances that may spontaneously combust, all of which share the characteristic of being ignitable. Thus, it is Hazard Class 2 that appropriately describes materials that can exist without a risk of ignition, depending on their specific properties.