Before driving a cargo tank motor vehicle with hazardous materials, what safety concern must be addressed?

The correct choice highlights the critical safety measure of ensuring that all manholes on the cargo tank motor vehicle are closed and secured before driving. This step is essential because manholes are access points to the tank that, if left unsecured, can lead to hazardous material spills or leaks during transport. The integrity of the tank is paramount when handling hazardous materials, as any unauthorized opening could create dangerous situations for both the driver and the environment.

Additionally, closing and securing manholes prevents accidental exposure to volatile substances, which could cause health risks or environmental contamination. Regulatory standards, such as those detailed in NFPA 58, emphasize that all openings must be properly closed and secured prior to transport to minimize the risk of incidents associated with hazardous material transportation.

Addressing the other options, while ensuring that the tank is filled to capacity, checking tire pressure, and wearing safety helmets are important safety practices, they do not directly relate to the specific concerns about preventing leaks or spills of hazardous materials during transit. The focus on securing the manholes makes it a paramount concern in the context of transporting hazardous materials safely.