Which BSL requires the use of a supply line respirator or work within a sealed glove box?

The correct answer is that BSL4 (Biosafety Level 4) requires the use of a supply line respirator or work within a sealed glove box. This level of biosafety is designed for work with highly dangerous and exotic pathogens that pose a high risk of aerosol transmission and for which there are no available vaccines or treatments. The use of a supply line respirator is essential to provide a protected environment for researchers by ensuring that they are not exposed to potentially infectious aerosols. Additionally, the sealed glove box provides a contained environment to handle these high-risk agents safely, preventing any escape into the laboratory environment.

Other biosafety levels have different requirements. For instance, BSL2 is equipped to handle moderate-risk agents and requires less intensive safety measures, while BSL3 is utilized for pathogens that can cause serious disease through inhalation but still allows for some flexibility in safety practices compared to BSL4. BSL1 is the lowest level and deals with minimal risk agents, which do not require special precautions like respirators or glove boxes.