There is a strict limit of time that people are allowed inside the pyramids on the tour precisely for the reason of oxygen concerns. Also, if the egyptians used some type of fire to light the inside labyrinths, then why are there absolutely no burn marks, of any kind?
Aside from the marks that came later, these can be dated because of carbon left behind after combustion, there are none that actually date to the time of the Egyptian civilization, during the pyramid building time.
Uh-huh. Let's assume this is true, though I have my doubts (I know you didn't personally inspect every inch of the pyramids for scorch marks, and no, "I totally saw it on this one website" is not in fact a good reason to believe something.)
So fire won't burn inside the pyramid you were in, but there's burn marks on the walls dated to post-construction? Strange, that. Doesn't make a lot of sense now, does it?
Think about it a little: the pyramids aren't hermetically sealed, they just have very low airflow because of the design. So if they sit there empty for a while, the oxygen content inside will be
exactly the same as in the air outside -- that's equilibrium. Now, if there are an assload of people or large fires inside, they will gradually use up oxygen. And if the airflow is low enough, the oxygen levels inside will drop, because replacement oxygen can't get in as fast as it's being used. But, seeing as the pyramids were
tombs, presumably they did not typically have crowds of people hanging out in them. (Just a thought there.) So when people
did go in, they would have started with normal oxygen levels and not had any problem with light.
Note in any case that if there's enough oxygen for you to not die, there's enough to keep a flame going. You may need something that burns at a relatively low temperature and/or creates its own draft -- such as an oil lamp -- but if you're not suffocating, there's oxygen there.
Oil lamps, of course, have been around forever. And they normally don't leave "burn marks" behind. But really, I'm sure it was probably the aliens. Or the Atlanteans, with their secret Glo-Stick technology.