Western logging railroads have had fire trains almost as long as they've been logging by rail. Even today, it's a necessity in some of the remote places trains run.
BNSF, and BN before them, and probably the GN and NP, also have/had them, especially in the Cascades and Rockies, but they've also been used in eastern Washington.
These aren't just "fire fighting cars", they're entire trains, usually with multiple tank cars, often connected by piping, so they can keep spraying for a long time before running for water.