have the North bound tunnel pollution levels been tested. How often, time of day, tunnel full or empty. At which part of tunnel is the testing carried out. As you would expect the highest point is the worst. If yes to the above, what are the results. What are the legal limits and who set them. Time frame July 2018.

---

TfL Ref: FOI-1362-1819

Thank you for your  request received by Transport for London (TfL) on 7 August 2018 asking for information about pollution levels in Blackwall Tunnel.

Your request has been processed in accordance with the requirements of the Freedom of Information Act and our information access policy. I can confirm we do hold the information you requested. You asked:

Have the North bound tunnel pollution levels been tested? How often, time of day, tunnel full or empty? At which part of tunnel is the testing carried out? As you would expect the highest point is the worst. If yes to the above, what are the results? What are the legal limits and who set them? Time frame July 2018.

There are three monitors evenly spaced along the length of Blackwall Tunnel. These are positioned at a 3.5m height on the side walls of the tunnel. These are continuously measuring Carbon Monoxide, Oxides of Nitrogen and Visibility and will activate the tunnel ventilation system automatically if a threshold is reached. The confined nature of the polluted air within the tunnel enclosure leads to relatively even mixing therefore the monitors are measuring close to the average pollution levels at any one time.

The thresholds for CO and NOx are measured in parts per million (ppm) whilst visibility is measured in metres.

If the value is greater than 5ppm for CO or 1ppm for NOx, or visibility less than 400m the fans will switch on and run at LOW state until the value decreases.

If the value is greater than 10ppm for CO or 5ppm for NOx or visibility less than 300m the fans will switch on and run at MEDIUM state until the value decreases

If the value is greater than 20ppm for CO or 8ppm for NOx or visibility less than 200m the fans will switch on and run at HIGH state until the value decreases

If the value is greater than 30ppm for CO or 10ppm for NOx or visibility less than 100m the fans will switch on an run at VERY HIGH state until the value decreases.

Please find attached the data for the three monitors within Blackwall Northbound Tunnel showing the Carbon Monoxide and the Oxides of Nitrogen for the whole of July 2018. These are known as entry, mid and exit.

The monitors are constantly measuring however will only record when there is a change.

The air quality levels within the tunnel are governed by the following:

• World Road Association PIARC (Permanent International Association of Road Congresses) PIARC 2012 : Road Tunnels: Vehicle Emissions and Air Demand for Ventilation
• Environment and Health & Safety Executive EH40: Occupational Exposure Limits
• Design Manual For Road and Bridges : Volume 2 Section 2 Part 9 BD78/99 : Design of Road Tunnels

Please see the attached information sheet for details of your right to appeal.

Yours sincerely,

Melissa Nichols

FOI Case Officer

FOI Case Management Team

General Counsel

Transport for London

Attachments

Back to top

---