Normally the forklift manufacture will state single person operation only apart from driver training purposes.
An operator also demonstrating a truck fault to an approved technician would also be permitted.
There is usually a warning plate / sticker stating single person only allowed in the cab stuck on the machine, it's normally inside the cab next to the data plate.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.