What is the air change requirement for a tunnel of 610 m (2000 ft) long with a diameter of 3.4 m (11 ft)?

One air change per hour is insufficient for a tunnel of this length and diameter and does not meet the minimum ventilation threshold required by the applicable standard.

Two air changes per hour falls below the required minimum for this tunnel classification and would not adequately maintain safe air quality.

A tunnel 610 m (2000 ft) long with a 3.4 m (11 ft) diameter requires three complete air changes per hour per applicable telecommunications and underground infrastructure ventilation standards. This rate ensures adequate removal of heat, humidity, and contaminants generated by cable systems and personnel activity. The requirement is based on the tunnel volume and occupancy classification defined in the relevant standard.

Four air changes per hour exceeds the required minimum and is not the standard specified for this tunnel size category.

Five air changes per hour is higher than required for this tunnel configuration and does not match the standard's prescribed rate.