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.

  • 3
    Just a clarification - people are not in the cars/coaches while traveling, correct?
    – JPhi1618
    Oct 23, 2017 at 18:11
  • @JPhi1618: Yes they are in the cars, inside a specially-built waggon.
    – tricasse
    Oct 23, 2017 at 19:31
  • 3
    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, 2017 at 19:55
  • 2
  • 1
    @owjburnham, Also this Halon installer has a questions page that says it is safe.
    – JPhi1618
    Oct 24, 2017 at 13:57

1 Answer 1


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.[...]

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