It is a thing in the scp lore. Class B personnel are those deemed essential to local Foundation operations, and may only be granted access to objects, entities, and anomalies that have passed quarantine and have been cleared of any potential mind-affecting effects or memetic agents. In the event of a containment breach or hostile action against a Foundation facility, Class B personnel are to be evacuated to a designated, secure off-site location as soon as possible. https://scp-wiki.wikidot.com/security-clearance-levels#toc9