Odd Language #212: Who Is Authorised?

There is a sign at my new job:
FIRE ASSAY
EMPLOYEES ONLY
NO UNAUTHORIZED
ENTRY

The issue: This is on a door to the Fire Assay area. Should it be read as “This is the Fire Assay area. Only employees are allowed in.” or “Only Fire Assay employees are allowed in.”? I had to ask, and it is the latter because of the lead compounds used.