How are air quality levels in the tunnel kept within the set limits?
• The M5 East tunnel’s air quality is monitored 24 hours a day by the tunnel operator, Baulderstone Hornibrook, Bilfinger + Berger Joint Venture (BHBB). An automatic ventilation system is used to manage air quality within the set limits or goals (see question 1). • However, in the event that air quality levels are approaching the set limits; the tunnel operator has a number of options at his disposal to protect the air quality for tunnel users. • These options include turning on additional fans located within the tunnel and exhaust stack and increasing the operating speed of those fans. This acts to provide more clean air to dilute vehicle emissions, thereby reducing pollutant concentration levels in the tunnel. • In extreme cases the operator may choose to limit the number of vehicles entering the tunnel, either by closing lanes or decreasing the allowable vehicle speed. This provides a buffer to allow the operator to improve the tunnel air quality for motorists.
