Ehh… I'm yet to read it thoroughly, but the translation seems to be off here and there.
Personnel performing experiments with SCP-1475-JP must gain permission from two Level 3 or more personnel
I think it's better to use "two personnel of Level 3 or higher" .
It is restricted to use SCP-1475-JP-13 in experiments.
This implies that they must use the 13th chair for experiment, but it's actually forbidden (as seen in the end of article).
and from that time becomes invulnerable to any interference that would cause harm.
The original text actually notes some examples, such as cutting from knife or burning via flamethrower.