Best way to convert seconds to hours:minutes:seconds

I have a table that stores elapsed seconds as a numeric value. There is
a PHP script that displays data from this table onto a web page. What
is the best way to display the elapsed time in an HH:MI:SS format?
Obviously the to_char function only works on dates, so I am not sure
how to go about this. Do I need to create an internal PL/SQL function
that is called from my PHP SQL?

Thanks.

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