I can think of a few reasons:

- Test commences prematurely when people are still around

- Test is aborted partway through but then spontaneously resumes when people have started coming back

- Error in design or failure of hold-down structure turns static fire into dynamic fire, moving fire to where people are

These are unlikely, of course, but they are the things we have to seriously think about and try to design out of the system in order to create safe systems.

No one should ever be that close, but it's a worst case scenario within the realm of possibility (people do get themselves into danger sometimes, for example by wandering onto a railroad track when there's a train approaching). I don't think it's unreasonable to reserve the 10 on the 1-10 scale for 'loss of human life'.

> Loss of human life in a static fire is criminal.

True. And yet it is not without precedent.

Scaled Composites had an explosion while performing a cold flow test of SpaceShipTwo’s engine which killed 3. https://www.latimes.com/archives/la-xpm-2007-jul-27-me-explo...

I mean, there was that one static fire recently where the rocket broken loose and started flying. This was not for from a populated area. Ok, maybe that was pretty criminally negligent.