A fire that would completely gut an apartment as it did with the Papadapolis's would've caused a partial (as in their floor and at least the one directly above and below theirs), if not full evacuation of the apartment building by the fire department. However, this did not happen.
If the fuse was still lit enough to start a fire, it would've continued burning until the firecracker took off not a few moments after he hid it. Which begs to question why a firecracker of any kind would be in a chemistry set, and how Webster wouldn't think that it would fly God-only-knows-where after it took off, causing damage in his room and possibly starting a fire anyways.