Some experiments require level 3 (L3) confinement for biological agents which can be spread and are pathogenic to humans. The L3 laboratory provides a high level of security, particularly through the filtration of air expelled outside. This allows viruses to be safely purified and stored or the observation of cells infected by:

• Non-genetically modified risk group 3 microorganisms (highly pathogenic in humans, but presenting a minor risk to the community, and against which prophylaxis or effective treatments are known). 
• Genetically modified risk group 3 microorganisms in which vectors or cloned sequences do not increase the risk level. 
• Genetically modified, non-pathogenic or risk group 2 microorganisms bearing either genes coding for proteins or high pathogenicity for humans, or large genome fragments of risk group 3 microorganisms or Ea3.
• Animal cells that express risk group 3 viruses or Ea3.
• Animal cells harboring expression vectors with genes coding for proteins of limited pathogenicity or fragments of unknown animal or human genomes or large fragments of genomes of risk group 3 microorganisms or Ea3. 
• Plant cells and transgenic plant cells producing Ep3 class viruses.