There's no standard number that insures absolute safety, such as 6, either. Every transaction is reversible, theoretically. If it was just confirmed, 1 block now, it requires less effort than one that's 100,000 blocks deep, but they're both reversible, with enough effort. The "6 blocks" is just a good tradeoff between time and security. Given that you own 40% of hashrate, you have 50.398% chances to reorg 6 blocks.

To go even deeper, cryptography isn't "absolutely secure" either. Theoretically you can find all private keys with bitcoin. Practically, it's impossible.

From my experience, the significant risk with Lightning is human error. There are some good odds to mess things up with the software, especially if you're not a techie.