Which of the following is critical when connecting to a fire department connection?

When connecting to a fire department connection, ensuring that the connection is tight and secure is essential. A secure connection helps prevent leaks that could compromise water pressure and flow during firefighting operations. The integrity of this connection is vital to maintain an effective water supply, which can make the difference in a firefighting scenario. If the connection is loose, it may result in a loss of water, which could hinder the response efforts and put lives at risk.

While checking that the valve is closed, verifying the operation of the water source, and checking the hose length are all important steps in the overall process of setting up a fire department connection, none of these steps directly affect the immediate functionality of the connection itself as the security and tightness do. Therefore, ensuring a tight and secure connection is critical to successful firefighting operations.