A simple question I imagine, but I am wondering how I would combat DoS
attacks by users holding the REFRESH key on their browsers?

I have reproduced this error on a PHP-MYSQL website and when I hold the
REFRESH key on for a while, page gen times shoot up dramatically and
hundreds of processes are created.

Is there a way I can stop this/limit the connections/processes in apache
conf/php.ini?

What can I do to combat this method of DoS?