Why do cars need to leave their windows half open whilst on the Eurotunnel?

Question

Whilst riding the Eurotunnel with a car, they ask you to keep your windows half open and also to open any sun roofs. What is the reasoning behind this?

I've checked their website and FAQ and couldn't find any information as to why. On board notices also do not mention the reasoning behind why they ask passengers to do this.

Just a clarification - people are not in the cars/coaches while traveling, correct? — JPhi1618, Oct 23 '17 at 18:11
@JPhi1618: Yes they are in the cars, inside a specially-built waggon. — tricasse, Oct 23 '17 at 19:31
Ahh, ok. I was one of the many that was under the impression that a Halon system was deadly to people. Turns out it can be safe. — JPhi1618, Oct 23 '17 at 19:55
You can either stay inside your vehicle or stand along side it, but are always near it — Draken, Oct 23 '17 at 20:52
@JPhi1618 What's your reference for a halon dump not being deadly? I assumed that in the case of a fire, they gave people time to leave the carriage before activating the fire supression system. — owjburnham, Oct 24 '17 at 06:38
@owjburnham It's all covered in the first article linked by the answer — Draken, Oct 24 '17 at 07:39
@Draken Well, you can also walk along the entire train, to the back, to the front, as you wish. Or at least you could some 15 years ago when I was young. — Jan, Oct 24 '17 at 07:46
@Jan You can still, though they do recommend someone stay near the vehicle due to theft, protectetion, etc. I shouldn't have used always, but often instead. Most people, from my several experiences, don't leave their cars as the trip is rather short — Draken, Oct 24 '17 at 07:49
@Draken from my dated experiences what you have said was correct then, too. (And it was my mum who was too lazy to join me and my dad exploring the train ;D) — Jan, Oct 24 '17 at 07:58
@owjburnham, Also this Halon installer has a questions page that says it is safe. — JPhi1618, Oct 24 '17 at 13:57

score 113 · Accepted Answer · edited Jun 25 '20 at 14:34

To allow for adequate fire suppression, in the event of a vehicle fire in the tunnel. The tunnel's fire suppression system depends upon complete mixing of the released halon gas with all air, without having pockets of high (or low) halon concentration. Check the document "EUROTUNNEL'S SPECIFICATION FOR HALON 1301 REPLACEMENT"; it claims (on page 271):

[...]The results proved that complete mixing did occur but also indicated that coach doors, roof vents and car windows needed to be open in order to ensure the Halon air mixture enters the coach and car passenger areas.[...]

on the web page with "Safety instructions" for coach operators, it says too:

[...]Open all doors, windows, air vents and skylights. This will allow all announcements to be heard and the automatic fire extinguishing system will be effective in case of fire on board your coach.[...]

Why do cars need to leave their windows half open whilst on the Eurotunnel?

1 Answers1