Which of the following represents the least to most levels of respiratory protection?

The correct choice reflects the order of respiratory protection devices based on their level of protection provided against airborne contaminants. An air-purifying respirator serves as the least protective option in this sequence because it filters out specific contaminants from the air; however, it does not provide oxygen if a situation lacks sufficient breathable air.

The powered air-purifying respirator builds upon this by utilizing a battery-powered blower to provide a continuous flow of filtered air to the wearer. This design enhances comfort and reduces breathing resistance compared to standard air-purifying respirators, though it still relies on the ambient air being safe enough to breathe.

Next in the hierarchy is the supplied air-respirator, which is connected to a source of clean air. This type of protection allows the user to be in environments that are heavily contaminated as they receive an uncontaminated air supply, thus significantly increasing safety compared to the previous options.

Finally, the self-contained breathing apparatus offers the highest level of respiratory protection as it includes a tank of breathable air. This design provides independence from the surrounding atmosphere, making it the best choice for scenarios where the air is toxic, oxygen-deficient, or otherwise unsafe.

The order presented in the correct choice represents a progression from the simplest filtration methods to complete