@RamenRider
There are some rules about SCP testing and storage that should prevent that. Namely that you aren't supposed to have tests done where they might interact with other SCP, if at all possible. There used to be a rule that Keter weren't even supposed to share a facility with any other SCPs, but I think that one went away as the number of SCPs went up and it became implausible to have that many Keter each with their own site.
@Boredtears If it can teleport a shark, it can teleport a Keter and a Keter breach is a Keter breach. You have more important things to pay attention to if the Keter alarm goes off.
Those events can only be generated if there’s a thrower, otherwise it’s harmless. Being dangerous doesn’t classify it as Euclid.
After some digging around, I found that some old SCP’s haven’t really been updated to the classification system (especially pre-1000’s as pointed by others here), so that explains that
That statement is actually incorrect. Being dangerous doesn’t classify an SCP as Euclid. Classification is determined by how easily an SCP can be contained.
Please kindly read Eldistan’s comment as they have posted the link to the SCP Object Classification explanation on the SCP website.
My favorites to read about are Euclid and Keter class SPCs because they tend to have the most horror. Either its something that'll end the world in some horrifying way or an SPC with a messed up effect or function like The Plague Doctor