What could happen due to the ingress of goaf gases at a positively pressured or leaking seal?

The situation described involves the ingress of goaf gases into an area with a positively pressured or leaking seal, which can create a serious safety hazard. The correct answer addresses the potential for the atmosphere to become irrespirable. This typically occurs when harmful gases, such as methane or carbon dioxide, accumulate in the environment due to leakage or poor ventilation. These gases can displace oxygen, leading to a reduction in breathable air, and may also bring toxic substances that make the atmosphere dangerous for occupants.

In contrast, the other options do not align with the expected outcomes of gas ingress in such a scenario. Improved air quality would imply that harmful gases are being filtered out or that the air is becoming safer to breathe, which contradicts the conditions described. Stable atmospheric conditions imply that the air composition remains safe and unchanged, which is unlikely when goaf gases are involved. Lastly, increased oxygen levels would suggest an enhancement of air quality, which is also contrary to the realities of gas ingress, where the introduction of harmful gases typically threatens the availability of breathable air.