Which general characteristic defines Class 2 gases in the HAZMAT classification system?

Class 2 gases in the HAZMAT classification system are characterized primarily by their ability to expand rapidly or exert pressure. This characteristic places them in a distinct category where they can pose various risks not only to the environment but also to human safety. The potential for pressure buildup can lead to explosions, as well as the rapid dispersal of the gas into the atmosphere, which may create hazardous situations.

Furthermore, these gases can exist in multiple forms, including compressed or liquefied states, and can change rapidly under environmental conditions. Understanding this characteristic is crucial for appropriate handling and emergency response measures, as the behavior of these gases under pressure is key to mitigating risks associated with their transport and storage.

Other listed characteristics, such as being highly toxic or stable and non-reactive, do not universally apply to all Class 2 gases, making those options less defining of the class as a whole. The focus on pressure and expansion makes the correct response particularly relevant to the classification and management of these substances in hazardous materials scenarios.