Hacker News Reader

Comment by cherryteastain | Hacker News Reader

> tunnel ventilation installations, chiller systems pumping chilled air into mid-tunnel shafts and regenerative braking to reduce heat generated by trains breaking

The hoops TfL jumps through just to not extend AC to the rolling stock in more lines are baffling. At least we finally got some AC in the new Piccadilly rolling stock.

View on HN

I think AC net adds heat to the system, we just don't usually care because the hot end is outside. Here the hot end of an ac unit on the rolling stock would be in the same clay-insulated tube and not escape, so I think it would be a problem? They have to get the heat out of the underground and up to the surface somehow.

AC will only make the problem worse in the long term. Picadilly got AC because it has above-ground sections.

You can redesign the signalling systems etc to work at even 40C, plenty of countries do it. You can't redesign humans to feel comfortable inside a stuffy carriage at 35C.

Sure, but that means the stations will also have 40C air. Can the humans handle that? And it's going to be 42C the next year, 44C the year after, and so on...

Platform screen doors can isolate tunnel temperatures from platform temperatures.

That doesn't help the people maintaining the tunnels and everything inside them.

What do you do if some incident halts full trains (possibly depowering them but for things like emergency lighting) near the midpoints of longer sections of 40 degC deep tunnels?

You can survive a few hours at that temperature, so not an immediate catastrophe. You should be still able (though not comfortable) to walk to the next emergency exit or station.

how many times has this scenario happened in last 20 years?

This is exactly the kind of thinking that lead to https://en.wikipedia.org/wiki/King%27s_Cross_fire

In safety engineering you do have to think about low-probability events.

Reply on news.ycombinator.com