Traditional insulation and non-combustibility are easily glossed-over topics. Ascertaining what constitutes passive fire protection, as opposed to risk reduction through provision of safe materials near passengers and operators, takes a reasonable sense of awareness and due diligence. Here is a guide to non-combustible acoustic treatments and insulation.

https://infrastructuremagazine.com.au/2019/10/08/what-does-safe-mean-in-materials-developed-for-tunnels-trains-and-transport/