Olaf,
A very interesting topic!
Let me try to get two of my own pictures from South Africa on here. (Trying out Flickr at the moment)
As is clearly visible the driver on Sandstone's NG 15 used the swing out seat to get to the cooling air.
Yes, as far as I know the swing out seats got introduced to the NG locomotives after the first NGG 13's were delivered.
Originally they even had doors to the cab. It does get really hot in the cabs of the NGG 13 and 16 Garratts.
During my visit to Sandstone in 2012 I got the chance for a cabride on NGG 13 No. 49. As the "third man" I had the unpleasant position of standing in the middle of the cab. When the firedoor started to change it's colour to a dull red my jeans simultaneously started to feel like they were burning.
A few days later I was firing this locomotive for a day. Due to it not having the swing out seats I was standing in the doorway to catch some fresh air.
While driving and firing the only Garratt we had here in Switzerland I never felt unsafe sitting outside the cab.
Very best Regards,
Urias