Final answer:
The most critical responsibility of an authorized entrant is to exit a confined space when they sense a change in the atmosphere due to the potential of extreme physical danger and the uncertainty of hazards, such as fire.
Step-by-step explanation:
The authorized entrant has a few responsibilities, like exiting a confined space when they sense a change in the atmosphere. In such situations, there is significant uncertainty over whether a serious fire or hazard awaits, presenting an extreme physical danger. Confined spaces are often not designed for continuous occupancy, and dangerous conditions can arise quickly, such as a build-up of toxic gases or a lack of oxygen, which can be life-threatening.
Exit is also critical when conditions are uncomfortable or upon completion of a shift; however, the immediate and critical responsibility is reacting to environmental changes. For example, if a sensor indicates a rise in carbon monoxide levels, this could signify a serious and imminent threat requiring immediate evacuation. Similarly, if primary communication is interrupted, such as through a phone call, the entrant must be able to quickly assess whether they can stay safe while remaining inside the confined space.