According to NFPA 1901, wheel chocks must be able to hold a fire apparatus on a ____________ percent grade with the transmission in neutral and the parking brake released.

The requirement that wheel chocks must be able to hold a fire apparatus on a 20 percent grade with the transmission in neutral and the parking brake released is established by NFPA 1901, which governs the specifications for fire apparatus. This standard ensures that fire apparatus can be secured against rolling when not in operation, especially on inclines, preventing accidents and ensuring safety during operations such as firefighting or rescue efforts.

A 20 percent grade is a steep incline, and the requirement for wheel chocks to secure the apparatus on such a slope reflects the need for reliable stopping power in challenging conditions. Firefighters often need to park their apparatus in various environments, including hilly terrains, where the effectiveness of wheel chocks is critical for maintaining the safety of personnel and the equipment itself.

Choosing a different grade such as 10, 15, or 25 percent would not align with the established safety standards that reflect the operational realities faced by fire departments. The 20 percent figure is specifically designed to ensure that fire apparatus remain secure under demanding conditions, making it the appropriate standard according to NFPA guidelines.