My understanding is that (1) is you deliberately did something that killed someone but your intent was not to harm them, say you’re working on a car you mean to scare them by faking dropping the engine on them, but actually do drop the engine, vs (2) you’re working with your friend on a car and drop the engine without knowing that they’re under it.
For (2) i believe that other things feed in to it - did you take sufficient caution, did you have reason to know there was someone there, were you following best practice, etc.
If you did literally nothing wrong (eg a completely freak accident) I don’t believe manslaughter would apply
IANAL though so don’t go dropping engines on people and blame me :)
