Booting a live ISO without mounting the hard drive ?

[linux guy]

I'm on the road, in the middle of nowhere.

I've got a hard drive issue.

I'd like to run the f15 Live ISO from a USB drive.  No problem there.

I DO NOT want it to mount the hard drive.   i'd like it unmounted so
that I can perform disk tests and stuff on it.

I know about rescue disks.  I don't have enough bandwidth to download one.

How do i run a Live ISO so that it doesn't mount the hard drive ?

Thanks