Using an internal hdd as external, unsafe ?

Is it dangerous to use an internal hard disk as external hard disk ?

Not at all, simply mount it in an empty box for external HDD.

But not exactly, I said internal, that means without the mount in a box ..

Ah ok, but it's more practical in a box (for the price it costs), and it will be a little more protected, but not until it falls to 1 meter, and you do not fit the part electronics on a metal plate, there is not too much risk (you have to still pay attention to components of the plate for the electronic transport).

In principle no problem.

Nevertheless, external hard drives are commonly used in USB or eSata.

Unlike in connectivity, for internal use, SATA cables are not shielded in any case much less than eSata. Not to mention the maximum length of 1m to comply with the standard sata cables, unlike eSata ranging 2 meters I believe.