I'm prone to agree with Geoffrey Drumm on that subject. He agrees that various ancient Egyptian structures were used for chemical plants.

In that video where Graham said that, he also acknowledged that the Great Pyramid had multiple functions so Graham would probably agree too.

If you check out that Once Bitten episode that just dropped yesterday, you'll get what I'm saying. The theory is in that episode and I bring lots of receipts. I presented this theory to a panel of PhDs and they loved it.