Fire truck manufacturers originally constructed their tanks from the same material used for the body. This evolution can be traced through different materials over the decades. Now in the modern day, steel is less common and materials like HDPE Plastic are taking center stage.
Polypropylene tanks are the standard in the fire service today. However, given the variety of applications, other materials might be better suited for specific functions. It is advisable to consult with the tank supplier or OEM for unique circumstances.