Apple Mac Pro (Mid 2010) - Manual (Page 39)

39 Chapter 3 Making a Good Thing Better
Opening Your Mac Pro
1 Before you open your Mac Pro, shut it down by choosing Apple () > Shut Down.
NOTICE: Always shut down your Mac Pro before opening it to avoid damaging
its internal components or the components you want to install. Do not open your
Mac Pro or attempt to install items inside it while it is on.
2 Wait 5 to 10 minutes to allow the internal components of your Mac Pro to cool.
WARNING: Let your Mac Pro cool down before you touch the internal components,
which may be very hot.