Orange Line has problems with power - passengers' commutes are fast going sour

A good 4000 amps of current (about what a typical train would draw) can accomplish quite a lot.

There have been press items on this regarding other transit systems.

Often what happens is that the metallic metal dust from the 3rd rail pick-up shoe scraping the power rail, and nearby support wheels-on-rails will accumulate due to a host of atmospheric conditions. When the space between the 3rd rail and support insulator becomes coated it can create a connection where current may flow. As the rust dust, which this is, heats up it carbonizes which increases the conductivity causing it to heat more. Eventually it will light up red hot and anything nearby such as newspapers and other trash can ignite.

The same is true when the 3rd rail show does not properly rest on the 3rd rail and it creates sparks. The sparks can also cause ignition of trash.

In some areas the system uses wooden support ties, usually at crossovers (switches) due to the need to accommodate heat and cold expansion-contraction, and easier maintenance and replacement of worn parts. Wood then can also become fuel.

Another reason is when power or ground connections fail or become compromised. That forces connections elsewhere to pick up the load, causing them to overheat and ignite. Think of it as an extension cord that has too many things plugged in to it.

None fo this is unnatural thing. It happens to all electrically powered transit systems at some point. There is no easy fix or panacea.