i'm not a chemist so take my words with a grain of salt -

google says the most dangerous bases can cause skin and eye damage, and be very flammable if they were to dissolve aluminium (two different chemicals). So I guess worst case scenario you open the windows, lock the room, and come back with protective equipment to clean up your mess

you probably wouldn't handle something, that if dropped, would be dangerous enough to need a whole building evacuated outside of a dedicated room without wearing a full hazman suit and adhering to additional 100 precautions and safety measures

unless you're the sort of guy to use a screwdriver to play with the demon core, but that's not a liquid chemical base and hopefully won't happen again

I was curious as well and in this article the only mention of dangerous bases is tert-Butyl lithium ("t-BuLi is very pyrophoric, it readily reacts with air catching fire, that’s why it has to be handled and stored with very special care, always under a protective inert atmosphere of pure nitrogen or argon"). But in that case you couldn't just drop it on the ground outside of a vent?

BRB, looking up the pH of chlorine triflouride....

Edit: Turns out it reacts explosively with water (so it itself can't form the aqueous solution necessary for the concept of pH to be applicable) and decomposes into two different strong acids (hydrofluoric acid and hydrochloric acid). So yeah, not a candidate for our mystery base.

tert-butyl lithium. Ignites on contact with air. Often used in conjunction with flammable solvents, so large fires and explosions are possible when working with large enough quantities.

As far as safety SOPs go, nearly any chemical spill of a large enough quantity warrants evacuating the area in many chemical safety plans. For some institutions, this is as little as 1 liter or 500g of material. This can obviously be overkill if you spill something that is relatively inert and non-toxic such as water or NaCl.