yep you guys are correct, brake cleaner is caustic and when burnt has very unpleasant fumes and those fumes can be harmful if you breathe them in directly or even indirectly.
And on that note i would say that starting fluid would probably be the best of the 2 mentioned but either one has its consequences if not used correctly.

Too much starting fluid and u lock up the engine and have to wait for it to dissipate before it will turn over again and in some cases it has a very bad reaction to aluminum pistons if used too frequently so that is why i said to use a light spray in the air cleaner only, NEVER spray it directly into the intake.

As for the brake cleaner i only mentioned that because it will run an engine if you do not have any starting fluid handy but like has been said... it has a very caustic pungent odor and will mess your lungs up pretty bad fairly quick if you breathe it in. So if you absolutely have no other choice but to use it i would do it in a very well ventilated area. Outside preferably :o)

and as for that article rcav8tor posted about that guy breathing in the vapors from the burning fluid on the diesel fuel tank, i'm sure that was not very good but there were alot of other factors that may have contributed to his condition like when welding there are certain gasses that can be produced even with no cleaning solvents being used that are generated from the heat and reaction to the metals themselves. The diesel tanks may have had coatings on them or a certain type of paint, and if they were galvanized that would have been very serious as galvanized metal produces poisonous gasses when heated and melted from welding, bad enough to kill you in just the manner he was describing.
When i worked for a cat dealer where i live we had a welder in our shop that was welding on some frame components and just the paint that was on the frame when burnt from the welder produced a toxic gas and it had such a bad effect on him he was sent to the hospital within 30 minutes, he fell out on the floor and almost died right there.
So yep i do agree there are many things that can have adverse effects on you that most people take for granted.
I myself am fairly fortunate i suppose, i have never had anything remotely like that ever happen to me over the years other than a bad headache from breathing in some of that crap on occasion.
I guess it can happen to anyone though and none of this should be taken for granted.
ALWAYS BE SAFE! and don't take ANY chances if you are not sure of what you are doing.