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April 19, 2019, 07:52:39 am *
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Author Topic: "I would recommend passengers to sit as far as possible from the engine ..."  (Read 552 times)
Adrian
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« Reply #15 on: April 14, 2019, 06:47:11 pm »

Whilst I understand 81D's misgivings about diesel fumes in stations (and the worst by far that I have ever encountered is on the footbridge at Manchester Victoria where the DMUs idle immediately below it), the original thread was about the on-train situation.

Something that crossed my mind is that these days the vast majority of stock is air conditioned and there isn't much stock still running with opening windows. As I see it therefore, if you are travelling in what is essentially a semi-sealed box, air pollution from outside whilst on the move is going to be minimal. And in addition, if pollution is coming into the coach via the aircon, it's not going to make any difference whatsoever which coach you are in.

So I suspect that this latest scare story report only really applies to older stock with opening windows.

 

Presumably there is some sort of filter at the air intake for air con.  But does it remove the fine particulates (PM2.5) that are now considered the most harmful?
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Bmblbzzz
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« Reply #16 on: April 15, 2019, 10:43:28 am »

Some studies have found that the air inside a car is more polluted than the air at the side of the road. The problem appears to be that exhaust gases from the vehicles in front are sucked into the car, either by air-con or simply by motion. Presumably it's a similar basic problem with trains, albeit the fumes are coming from the train's own engine not other trains'. But it must vary a lot with airflow, which is going to be affected by all sorts of fixed and changing factors (like shape of vehicle and speed).
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stuving
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« Reply #17 on: April 15, 2019, 11:15:47 am »

I think air-con is a red herring. It cools internal air, in most vehicles entirely by recirculating it. The external part of a train roof is of course just a heat exchanger rejecting heat to outside air. (More or less) fresh air for make-up, or for ventilation without the chillers in use, is what matters and that's what tends in cars to come from low down in front of the engine - good to avoid your own chariot's effluvia, less so in respect of the one in front's exhaust.

As to where the ventilation intakes are on trains, in general or specifically, I can't say I've looked. I vaguely recall seeing grilles on the sides of carriages, but they could for inlet or outlet. 
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Western Pathfinder
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« Reply #18 on: April 15, 2019, 02:06:46 pm »

Air conditioning in most vehicles actually conditions fresh air by cooling  after it has been drawn into the said vehicle through a particulates filtration unit usually referred to as a Cabin or Poles filter. This filters all the air drawn into the car regardless of whether the AC is in operation.
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stuving
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« Reply #19 on: April 15, 2019, 03:21:41 pm »

Air conditioning in most vehicles actually conditions fresh air by cooling  after it has been drawn into the said vehicle through a particulates filtration unit usually referred to as a Cabin or Poles filter. This filters all the air drawn into the car regardless of whether the AC is in operation.


You're right about cars - it seems the heater/chiller box is usually fed via a flap valve that selects all external air, unless you select recirculate in which case it all comes from the cabin. And as to the inlet, that used (on old cars like mine) to be a grille under the windscreen - that's gone, but I guess the inlet is still thereabouts.

But the point I was trying to make about all vehicles is that the freshness or contamination of the air does not depend on where the chiller is.
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Bmblbzzz
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« Reply #20 on: April 15, 2019, 06:12:14 pm »

This is all ultimately distraction though: the key is not avoiding sitting in the pollution, but avoiding making it in the first place.
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