I’ve tried using disk utility and didn’t seem to get anywhere. Using linux’s dd command seems to work best.
Step 1.
Open up the Terminal app and enter in:
diskutil list
Figure out what your usb device is called – mine was called /dev/disk1.
Step 2.
Unmount the disk:
diskutil unmountDisk /dev/disk1
Step 3.
Copy the iso to the USB:
dd if=image.iso of=/dev/disk1 bs=8192
Step 4.
Eject the disk:
diskutil eject /dev/disk1