understanding biosafety levels bsl1 to bsl4 stratifying biohazard risks in laboratory settings for enhanced safety and

biosafety level bsl1 bsl2 bsl3 bsl4 biohazard laboratory safety infection risk bacteria bioweapon hazard personnel assessment sign warning microbiology virology bacteriology pathogenic infectious disease biosecurity containment precautions research science healthcare management epidemic biological threat agent high low moderate extreme biodefense public health training emergency preparedness protocols environment pathogen handling control facility scientific