BSL-3 stands for Biosafety Level 3, which is a set of safety protocols used in laboratories that work with pathogens that can cause serious or potentially lethal diseases through inhalation. These labs are designed to prevent the escape of harmful microorganisms and require specialized ventilation systems, controlled access, and personal protective equipment for researchers. In a BSL-3 lab, researchers handle agents like Mycobacterium tuberculosis and certain viruses that can lead to severe health risks. The facilities are equipped with features such as sealed windows, negative air pressure, and air filtration systems to ensure that any airborne pathogens are contained and do not pose a risk to the surrounding environment.