Level B radiation gear is a type of protection used by Space Pirates that is alluded to in a scan in Metroid Prime. It is said in the scan that it is used as protection from Phazon radiation in Phazon processing areas. This technology is a precursor to the Hazard Shield, as both protect from the damaging effects of Phazon exposure.
Metroid Quarantine B
"Health Alert: Phazon radiation warning is still in effect. Do not enter a Phazon processing area without Level B radiation gear. Prolonged exposure is 100% fatal."