Carbon Monoxide content
Folks that suffer from asthma should avoid diesel exhaust, and certain sufferers have a very low tolerance level for it. This is one thing that actually shows up in people almost immediately, sometimes within minutes, unlike cancers that may take years to manifest. I haven't heard of anyone dying from exposure to diesel exhaust, but a good asthma flare induced by the fumes will make you think you are going to expire. Very miserable.
It won't be so prevalent now with ULSD, but many people have an intolerance to the smell of sulphur fumes in diesel exhaust. Symptoms include runny nose, watery eyes, or burning sensation in eyes. Some people have major intolerance to sulphur. I myself can't be in the vicinity of anything that burns bunker fuels (Lots of sulphur) for more than a very few minutes. Severe headache and nausea follows exposure quickly. My wife can not be in vicinity of any diesel or JP fuel exhaust at all. Major migraine headache almost immediately is result.
The 8.2L Detroit's and Cat 3208's used in class 7 trucks for years would, at idle, make almost everybody standing close by sick. When you had to have truck running for air compressor and crane use, well, it was bad. Cummins engines with the old PT fuel systems would slobber and stink real bad at temperatures below zero. Bringing one of them into a shop from outside on a frosty morning meant you would cough and have runny eyes for an hour and stink for the rest of the day from the raw unburnt fuel impregnated into your clothes. Combination of cold damp air and nasty exhaust made everybody miserable.
We older chaps have worked in enclosed spaces full of diesel smoke for years. Mines, buildings, and equipment cabs are all examples. Can't believe that all the soot and fumes we breathed was good for us. Mining machinery at least usually had scrubbers mounted that helped some.
When cleaning sediments out of large oil tanks in California, all our operators had to use supplied air systems, though this was as much due to the heavy oil fumes inside as much as anything else. But even with massive ventilation, diesel exhaust was still bad inside and many operators could not stay in the seat of those machines very long before being sickened.
I'm a little surprised that anyone would run a diesel in a building with people present these days, or, upon re-reading your post, was the equipment outside in close proximity? Natural gas or propane powered equipment would be a far better choice and electric power better yet in either situation. But maybe just closing doors and windows would have taken care of the problem.
These folks you mention are likely responding to all the recent hype in the media about carbon monoxide and carbon dioxide. They may have smelled some odor and it may have sickened some for a bit. In all likelihood, they need to raise a stink of their own with whomever is working with the diesels in or by the building and get those people to switch to some other power sourced equipment if possible.
If no alternative, building management should remove affected people to another building for duration of work.