If the room you’re in suddenly went dark and filled with smoke, would you be able to get to the fire escape? That was the question put to me many years ago by a friend who, like me, often stayed overnight in unfamiliar locations. I think he took it to extremes, though, in travelling everywhere with a thirty-foot climbing rope in his suitcase, but his point was sound. A few years later, when I was stood outside a hotel after a fire alarm in the late evening, I was glad to have taken that advice.

Much of what we do on our Macs can be at worst relatively harmless, and there are simple measures we should take to ensure they’re safe. Accidentally delete the wrong files, and you should be able to restore them swiftly from your latest backup. Cut out a crucial section of a document, and you should be able to look back through its saved versions and paste the text back from one of those. That’s why we have all those checks and safeguards.

Every so often, though, we do something that could have greater consequences, like adding another volume to our boot disk, or installing an alternative operating system such as Asahi Linux. Those are the times we need to check where the fire escape is.

If anything goes wrong with the containers and volumes on the internal storage of an Apple silicon Mac, the result can be serious, because these Macs have to start their boot process from there.

Intel Macs, including those with T2 chips, can of course start up entirely from an external disk. Although that might appear advantageous, in the long run it’s not as good as it might seem. Those with the added boot security that comes with a T2 can only boot from an external disk when that has been specifically enabled in Startup Security Utility, in Recovery mode, and the time to think about that isn’t when it can’t boot from its internal SSD.

Unlike Apple silicon Macs, though, Intel Macs with T2 chips can’t boot from an external disk in full security. In practice it means that, if you do enable that, anyone can attach any bootable disk to your Mac, start it up from that, and make off with it. So making the decision whether to enable your T2 Mac to start up from external disks will either compromise its security or its recoverability.

There’s no compromise of security when booting an Apple silicon Mac from an external disk, as that can only happen when that disk has a LocalPolicy created for it, that in turn requires ownership, and secure controls from the internal SSD. But if the internal SSD has become messed up, that Mac may well not get as far as considering starting up from the external disk, and all you can hope for is that it will be able to enter Recovery or Fallback Recovery.

If this all seems more complex and fiddly in Apple silicon, in practice it’s not, as boot failure is far less likely, and in most cases can be managed fully in either Recovery mode. However, making changes to the layout of containers and volumes on the internal SSD is one situation where an Apple silicon Mac’s ability to boot can be compromised. The Asahi Linux Project has drawn attention to one mistake that can spell disaster, removal of the Apple_APFS_Recovery partition/container from the internal SSD.

Let’s assume that you’ve changed partitions/containers and/or volumes on your Apple silicon Mac’s internal SSD, and want to revert to its original layout. You now have a choice of attempting that in either Recovery mode, using the diskutil command tool there, or putting your Mac into DFU mode and performing a full Restore with the IPSW image file for the macOS version of your choice.

Provided you have a second Mac and USB-C cable to connect it, and a recent full backup available to migrate from, Restore in DFU mode is likely to prove the simpler and more reliable option. Unless, that is, you’re the kind of person who also likes hoisting out your car engine and disassembling it on your kitchen table.

For all its apparent complexity, this is where an Apple silicon Mac comes into its own, as you can now Restore it to Sequoia even though Apple still so earnestly wants you to savour the delights of Tahoe’s Liquid Glass.

Follow my friend’s advice. When you’re about to do something that could have serious consequences, check where the fire escape is, as one day you may well have to rely on it.