Final answer:
The barrier to prevent unauthorized entry is an B. engineering control, which is a modification to the environment to reduce risks, different from administrative controls and personal protective equipment.
Step-by-step explanation:
The type of control represented by installing a barrier to keep unauthorized workers from entering a confined space is an engineering control. Engineering controls refer to any modification or addition to equipment, tools, or the environment that reduces the risk of hazards. This can include physical barriers, ventilation systems, and machine guards, among others. It is distinct from administrative controls, which involve changes in the way work is performed, such as scheduling or the implementation of safety procedures. Personal protective equipment (PPE) refers to special gear worn by individuals to protect against specific hazards, like the protective suit mentioned that is used by workers in BSL-4 laboratories to safeguard against biohazards. The suit described with its own air supply and ability to maintain a positive pressure, ensuring safety in case of leaks, is an example of PPE.