Edit: The physics

- (lambda) = c / 1,620,000 Hz = 185 m :: 1.62 MHz is what I derived as a near max possible accidental frequency able to be produced by AM equipment

- 185 m / 2 = 92.6 m :: this is half a wave length

In order to resonate (let alone have enough power to "cook", which I didn't even look at because the wave can't even resonate), a tunnel must be at 92.6 m (fundamental) or 185 m wide or tall (2nd harmonic). Most tunnels are ~5m/3m wide/tall at most.

Dusted off my physics from my minor in college so someone feel free to correct me.

[0]: https://wwwn.cdc.gov/NIOSH-Mining/MMWC/MineDisasters/Table

This system operates according to TFA up to the end of the AM band at roughly 1600 KHz, so 180 meters and change.

The danger is more likely there because someone might enter the tunnel and hit the feeder, which depending on the design can carry considerable power.