What physical property is indicated by SAE numbers in relation to fire apparatus?

The SAE (Society of Automotive Engineers) numbers specifically relate to the viscosity of oils and fluids, which is essential for the operation of fire apparatus. Viscosity is a measure of a fluid's resistance to flow; therefore, understanding the viscosity of the oil used in the machinery and equipment helps ensure optimal performance under various temperature conditions.

Oils with different SAE classifications have different viscosities, which affects how easily they can lubricate engine components and operate hydraulic systems. In the context of fire apparatus, using the correct viscosity oil is crucial for maintaining the operational efficiency of the equipment and ensuring its reliability during emergencies.

This understanding of viscosity also allows operators to select appropriate lubricants for the specific environmental and operational conditions, thereby enhancing the longevity and functionality of critical firefighting equipment.