Which class of fire is involved when filing a cabinet of old invoices is burning?

The correct response is that the situation described involves a Class A fire. Class A fires are those that involve ordinary combustibles such as wood, paper, cloth, rubber, and many plastics. Since a filing cabinet of old invoices is primarily composed of paper, it falls squarely within this category.

Understanding fire classifications is crucial for effective fire safety management and response planning. In contrast, Class B fires involve flammable liquids and gases (like gasoline and paint), Class C fires involve energized electrical equipment, and Class D fires pertain to combustible metals such as magnesium or potassium. Consequently, these other classifications would not be applicable to a fire involving paper products.