Can it be dangerous and who should I call?

Of course it could be dangerous but the smell needs to be explained more? A smell of sulfur or rotten egg smell could mean you are smelling the additive put in natural gas to give it an odor and make a leak detectible. Is it like a dead animal smell? Then it is not as dangerous hunt it down and dispose of it... if it a natural gas smell your local fire dept can be called and they will test the area or your gas co can come out as well. Good luck