What is the purpose of negative-pressure fans in firefighting?

Negative-pressure fans are specifically designed to create a vacuum that helps remove contaminated air from a building, particularly during firefighting operations. By drawing air out, these fans help to reduce the concentration of smoke, toxic gases, and heat within a structure, improving the safety for both firefighters and potential victims inside. This process is vital for maintaining a safer environment during an incident, allowing for better visibility and improved conditions for rescue and firefighting efforts.

While the other options may relate to firefighting and ventilation in some manner, they do not accurately describe the function of negative-pressure fans. Instead of introducing air or cooling the space, the primary intention of these fans is focused on extracting harmful substances, making option B the most effective choice.