What must be installed if intake air travels across the face of a permanent seal?

When air travels across the face of a permanent seal, it is critical to monitor the composition of the air to ensure safety in the mining environment. The installation of a monitoring device specifically designed to detect oxygen and carbon dioxide concentrations helps to maintain air quality and assess potential hazards. This is particularly important in underground mining where changes in air composition can indicate issues such as the presence of hazardous gases or inadequate ventilation.

In this context, monitoring devices provide real-time data that can alert personnel to dangerous conditions, ensuring that corrective actions can be taken to protect the health and safety of workers. The focus on monitoring oxygen and CO2 levels is essential due to their direct implications for mine safety, including the risks of asphyxiation or toxic exposure.

While other options may seem relevant, they do not directly address the need to monitor the air quality in relation to the incoming air stream across a seal. Thus, installing a device for detecting these critical gas concentrations is the most appropriate requirement in this scenario.