It is created by bombarding U-238 with neutrons. It has a radioactive half-life of 24,000 years. Pu emits alpha particles. These high-energy particles are more damaging than beta or gamma radiation, but can be stopped by a sheet of paper. Consequently, the major risk from Pu is inhalation or ingestion.
Tiny particles can lodge in the lung.
Livermore is a multi-purpose research lab with nuclear weapons development as its primary mission. LLNL fashioned the plutonium cores for full-scale bomb tests of its nuclear designs. LLNL currently has 880 pounds of Pu in stock, nearly enough for 100 modern nuclear bombs. Several of the Lab's buildings store, handle, package and machine radioactive materials and metals. By far, the building that handles the most plutonium is the rightly named Plutonium Metallurgy Facility and Central Vault, or Building 332.