A biohazard was a biologically hazardous substance, which had the ability to kill or severely incapacitate biological organisms.
Day 3
During Day 3, the terrorist attack was based around the immunopulmonary Cordilla Virus.
Day 5
During Day 5, the canisters of Sentox VX1 nerve gas were marked with the Biohazard symbol.
Day 7
During Day 7, the Prion variant posed a biohazard and threatened the life of Jack Bauer when he was exposed to it.