Just be sure your exhaust system is in good shape. Diesels do emit carbon monoxide gas which is poisoness.
Breathing bonds oxygen to the blood in you body and it gets carried around you body to muscles, heart etc. You need it or the boy passes out
The problem is that carbon monoxide bonds to the blood 200 times faster then oygen, If your sitting there not doing much, this goes unnoticed until you do some phyical work, when you stand up, walk,etc then you pass out from the lack of oxygen!
If you pass out in the area with the co in it, you will never wake up to get out.
I've had some first hand expierence with this (not in a vehicle, propane furnace in our bunkhouse trailer) and it sneaks up on you.
If being in a machine makes you drowsy, dizzy, sweaty and uncomfortable, stagger, vomit these are all prime symtoms of co poisoning
We were vary lucky.
Ken