I'm correcting something which my friend wrote. He wrote about incidents that had occurred while working in a mine, and stated that although the cause of each incident may have been different, they had in common a single reason: the workers did not follow the rules.
Here is the sentence:
Although, the causes of each incident may have been different, the same common reason applies:...
I believe that placing a comma after although is incorrect. My friend believes that it is correct. Would you please shed some light on this?