Class 5.1 materials are defined as:

Class 5.1 materials are classified as oxidizers, which are substances that can enhance combustion by releasing oxygen or other oxidizing gases when they undergo a chemical reaction. These materials are crucial in various industrial applications but pose significant hazards because they can significantly intensify fires and can react violently with combustible materials.

Understanding this classification is essential for proper handling, storage, and transportation to prevent accidents that can arise from their reactive nature.

The other options pertain to different classes of hazardous materials: spontaneous combustibles are categorized differently, and while toxic and infectious materials fall under another classification, and flammable liquids are also a separate category. Each type has distinct characteristics and safety protocols, underscoring the importance of proper identification in hazardous material management.