What type of air supply system is NOT typically found on rescue vehicles?

The correct choice identifies oxygen tanks as not commonly found on rescue vehicles as a primary air supply system. In the context of rescue operations, the emphasis tends to be on breathable air supplies that can support personnel in environments with poor air quality or in situations where they are at risk of inhaling harmful substances.

Breathing air compressors, which purify ambient air to create a breathable air supply, are routinely included on rescue vehicles to support firefighters and rescue personnel in hazardous conditions. Cascade systems serve as an effective means of storing and distributing high-pressure air cylinders, which are essential for longer operational periods in confined or dangerous areas.

Nonbreathing air compressors, although less common than breathing air systems, are sometimes utilized in specialized operations such as certain industrial environments where ambient air might not be safe for breathing, but these are still designed for specific applications rather than general rescue scenarios.

As such, oxygen tanks, while critical in medical scenarios or certain patient care contexts, are not typically part of the standard operational air supply systems necessary for rescue operations where breathable air is the immediate requirement. Hence, the choice of oxygen tanks as an answer reflects an understanding of the typical configuration and functions of rescue vehicles.