Checking the fluid level is done according to?

The correct answer is based on the importance of adhering to established departmental standard operating procedures (SOPs) when checking fluid levels in aerial ladders. Department SOPs are developed to ensure consistency, safety, and compliance with local operational requirements. They often incorporate best practices, training, and specific instructions tailored to the equipment and context in which it is used.

By following these procedures, firefighters can ensure that the equipment is functioning properly and minimize the risk of performance failures during critical situations. Variability that might come from personal discretion or relying solely on manufacturer guidelines can introduce risks, as department SOPs take into account the specific circumstances and operational needs of the local fire service. National standards may provide a general framework, but the SOPs are specifically crafted to align with the department's operational protocols and safety measures.