What must the ventilation system be in areas where explosive or flammable vapors, fumes, or dust are generated?

The ventilation system in areas where explosive or flammable vapors, fumes, or dust are generated must be interlocked to ensure safe operation. An interlocked system is critical because it helps to prevent the simultaneous operation of equipment that could create an ignition source when hazardous conditions are present. By controlling the interaction of different components, an interlocked system enhances safety by ensuring that, for instance, exhaust fans and supply air fans operate in a coordinated manner, thus minimizing the risk of explosions or fire.

In environments with volatile substances, maintaining a safe air balance and ensuring that any potential ignition sources are suitably managed are paramount. An interlock can help to ensure that ventilation begins before equipment such as tools or heating elements that could spark are activated, thus providing a fail-safe mechanism to protect workers and facilities.

The other options suggest alternatives that do not specifically address the necessary precautions against ignition sources in hazardous locations. Noncombustible systems do not address the operational interactions needed to ensure safety. Independent systems lack the coordinated safety mechanisms of entire systems working together, and the prohibition of systems would not provide a practical approach to ensuring safe ventilation in dangerous environments. Hence, the interlocked ventilation system stands out as the necessary requirement for ensuring safety in these high-risk areas.