[Vo]:Breathable Oxygen

[Harry Veeder]

When hydrogen is burned in air, the oxygen in the air combines with hydrogen
to form H2O. Will breathable oxygen decline if we burn too much hydrogen?
I guess this would never be a problem if all the hydrogen burned comes from
the decomposition of H2O into H2 and O2.

But seriously, if everything was powered by burning hydrogen would the
proportion of oxygen in the air gradually decline?

For that matter, has burning hydrocarbons already decreased oxygen
levels?

Just wondering...
Harry