There should be no dead men (or dead women) trying to sit upright in a forklift, much less trying to drive one. we don't need a -dead- man switch, we need "operator in position" sensors. (insert big stupid looking one tooth rednecky grin here)
For in depth information about US forklift manufacturing standards, check out the itsdf dot org website for the standards for US made units.
In the USA, I think starting in 2007, for the standard size units*, most every manufacturer is including some sort of Operator presence sensor system that will lock out lowering as well as travel and lift if no one is in the operators position.
this includes diesel and LPG, and makes lowering included in the electric units.
There is a "general requirement" to make the machine as safe as possible/reasonable, and if everyone else machines have operator presence sensors, (that do a, b, AND c,) and you fail to include them as cost saving, and someone gets hurt, can you not hear that attorney ask if it saved any money after the jury comes back with the award?
*standard size units does not include really huge trucks like full container handlers, as far as I know.