RR757 - Real-time measurement of nitrogen monoxide in tunnels and its oxidation rate in diluted diesel exhaust

Exposure to oxides of nitrogen (NOx which denotes the mixture of nitrogen monoxide, NO, and nitrogen dioxide, NO2) commonly arises in the tunnelling industry from diesel engine exhaust emissions and from the use of explosives. The British Tunnelling Society (BTS) guidance levels for NO are 5 ppm for an 8 hour time weighted average (TWA) and 15 ppm for a 15 minute short term exposure limit (STEL). Real-time monitors are used by the construction industry as they provide a means of checking that controls are effective. Previous laboratory work at HSL evaluated various commercial detectors potentially suitable as portable monitors and studied the conversion rate of NO to NO2 in air using pure gases (ie NO and air). This current project investigated:

  1. the field use of NO and NO2 monitors in a small sewer tunnel under construction to assist the determination and application of effective controls in order to maintain a safe working environment. Furthermore, a large road tunnel under construction was visited to study the fixed NO monitoring system installed there.
  2. the conversion rate of NO to NO2 using air-diluted diesel exhaust.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

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Updated 2021-04-23