Mr heater giving off smell stinging my eyes

You have several areas of concern here:

1---Ignition hazard, if you are working in an area with gasoline, paint or other flammable materials. One thing that helps is elevating the heater. Codes require any ignition source in a garage to be at least 18" off the floor.

2--Products of combustion of the unit itself. Poor ventilation makes this worse, as does poor ventilation ALSO causes worse combustion in the heater, ramping up the amount of CO (monoxide)

3--Mixture of the heater combustion and combustion products with shop chemicals. I used to service HVAC, and anyplace such as bodyshops, beauty parlors, laundries, photo/ print shops, that had much in the way of chemicals were VERY hard on heat exchangers and combustion chambers of older gas units without outdoor combustion air intakes.

ANY chemical, cleaner, thinner, etc, etc, in your shop is drawn into the burner and reforms into "something worse."

Probably the best/ worst example I can think of is the older HC based refrigerants, R-12/22, etc. You run those through a burner, and you get DEADLY PHOSGENE gas. Yeh....Just like Hitler used!!! You ever get a whiff of that, it feels like a knife up your nose!!!