Which class pertains to harmful substances that can cause injury or death if inhaled or ingested?

The classification of "Poison" specifically refers to substances that are capable of causing injury or death through ingestion or inhalation. These materials can disrupt normal biological functions at low levels and are typically characterized by their toxic effects on living organisms.

When considering the nature of poisons, it's important to note that they can come in various forms, such as solids, liquids, or gases, and can have different routes of entry into the body, with inhalation and ingestion being the most critical for the purpose of this question. Understanding this classification is vital in HAZMAT operations, as the presence of poisons necessitates careful handling, appropriate PPE (personal protective equipment), and effective response strategies to prevent exposure.

In contrast, other classes, while they may pose significant dangers, do not specifically fit the criteria defined in the question regarding injury or death from inhalation or ingestion. For example, radioactive materials primarily pose risks through radiation and require different protective measures, while corrosives primarily cause damage by direct contact with tissue. Flammable solids are dangerous due to their ability to ignite and cause fires, but they do not inherently present toxic risks through simple inhalation or ingestion.