There are a number of fire departments on LI with pipes laid under tracks to feed hoses through in the event of a major incident. Also, I have seen plenty of hoses stretched over the tracks, and as a fire dispatcher, I have called on numerous times to stop trains. As a fireman, i have put hoses under tracks myself. As a caution, when the request to stop or slow is first made to the RR, we set out highway flares on the tracks in the affected area, 1/4 mile away from the incident, on both sides to warn engineers in the event the radio message is delayed. If you live and respond in a district with railroads, you learn this is something you have to do. You have to keep your ears and eyes open all the time. My department has had plenty of interaction with the RR (train vs. pedestrians) so we are familiar with these safety rules. I don't live in third rail territory, I wouldn't be in a big rush to stretch hoses across the tracks in electric territory. Maybe a fireman in that area could fill us in...
I know it turns the RR on its ear, and the movement bureau gets bent. However, emergency situations take presidence, and as far as I know a fire chief or police officer handling any emergency has authority over the entire scene, with authority to close roads, rail lines, and direct evacuations if the public is in harms way.