I have been scouring the web searching for an answer to this question. I couldn’t find any specific web sites declaring it’s potential health risks but I was under the impression that it was dangerous to inhale and caused vein constriction in the brain.
Any help?
Is natural gas dangerous…sure, it ain’t air. Will you be harmed if you get a whiff of it? Nah. Any gas other than air or oxygen and nitrogen mix isn’t meant to breath.
Natural gas is dangerous however, in the fact that it is flamable and could explode if the concentration is high enough and comes into contact with spark or flame.
If you smell an odor of natural gas, leave your door open as you leave and call the gas company, they will have someone there very quickly.
Natural gas with ethyl mercapten in it will typically gag you badly before you inhale enough to hurt yourself.
BTW, according to Principles of Combustion by Kenneth K. Kuo (KKK? That’s not good! 
), the lower and upper limits for flammability of natural gas in air are:
Gas Lower (vol %) Upper (vol %) Stoich (vol %)
Methane 5 15 9.47
(approx. natural gas)
Heptane 1 6 1.87
Hydrogen 4 74.6 29.2
Carbon Monoxide 12.5 74.2 29.5
Acetylene 2.5 80 7.7
Ethane 2.82 15.34 5.64
Ethylene Oxide 3.0 100 7.72
Propane 2.05 11.38 4.02
Methanol 5.88 49.94 12.24
In case anyone cared…
Natural gas is mostly methane, which is only a simple asphyxiant (i.e., it works by displacing oxygen in the atmosphere). But natural gas contains other chemicals that are chemical asphyxiants (they work by causing chemical reactions in the body that somehow impair respiration). At least two minor constituents of natural gas are chemical asphyxiants:
I don’t know if the concentration of either chemical in natural gas is high enough to worry about.
From this source at the National Renewable Energy Labs:
“Natural gas containint H[sub]2[/sub]S is sweetened…to less than 4 ppmv.”
And although it is not mentioned there, I can give an unreferenced value of from 0 to 100 ppm for CO in natural gas, typically below 10 ppm.