Nitrogen Dioxide Monitoring

What is nitrogen dioxide monitoring?

Nitrogen dioxide monitoring measures the airborne concentration of nitrogen dioxide from combustion, diesel exhaust, welding and certain chemical processes that workers may breathe in during normal operations. It quantifies real personal exposure so employers can judge whether existing controls are adequate.

IndustrialAirMonitoring.uk provides independent nitrogen dioxide monitoring across foundries, vehicle workshops, tunnelling, manufacturing, welding sites throughout the UK. Our occupational hygienists deliver defensible exposure data that demonstrates compliance with the Control of Substances Hazardous to Health Regulations 2002 (COSHH) and the workplace exposure limits set out in HSE guidance note EH40.

Why nitrogen dioxide monitoring matters

Under COSHH Regulation 10, employers must monitor exposure to hazardous substances where it is needed to protect health, where a workplace exposure limit could be exceeded, or where control measures need to be verified. Nitrogen dioxide monitoring provides the objective evidence that satisfies this duty.

Uncontrolled exposure to nitrogen dioxide is linked to airway inflammation, reduced lung function and aggravation of asthma. Beyond the legal duty, robust monitoring protects your workforce, reduces the risk of enforcement action and civil claims, and gives insurers and clients confidence that exposure is being actively managed.

How we carry out nitrogen dioxide monitoring

We measure exposure using direct-reading electrochemical detection and sorbent (passive/active) sampling, following the recognised EH40 / MDHS methodology. Personal samplers are worn in the breathing zone for a representative full shift to derive an 8-hour time-weighted average, while static (background) samples help map contaminant sources across the workplace.

Samples are analysed by an accredited laboratory and the results compared with the relevant occupational exposure limit. Where short-term peaks are a concern we add 15-minute short-term exposure limit (STEL) sampling, so both the chronic and acute risk picture is captured.

Standards, limits and reporting

The current workplace exposure limit for nitrogen dioxide is 0.5 ppm (8-hour TWA), 1 ppm STEL (EH40/2005, as amended). We assess compliance using the BS EN 689 statistical decision framework, which accounts for exposure variability rather than relying on a single result.

Your report sets out the measured concentrations, the compliance position, the adequacy of existing controls such as local exhaust ventilation, and a recommended re-monitoring interval. It is written to be understood by managers and to satisfy HSE inspectors, auditors and insurers.

Our nitrogen dioxide monitoring process

Our nitrogen dioxide monitoring programmes follow a structured, four-stage workflow so the results stand up to scrutiny. Request monitoring or book a site assessment to begin.

1Scoping & site survey. We review your processes, COSHH assessments and previous nitrogen dioxide monitoring data, then plan a representative sampling strategy using BS EN 689 similar exposure groups.
2On-site sampling. Qualified occupational hygienists carry out calibrated breathing-zone and static measurements across a representative shift, with full chain-of-custody documentation.
3Accredited analysis. Samples are analysed using the relevant MDHS / ISO laboratory method and the results are compared against the applicable workplace exposure limit.
4Reporting & recommendations. You receive a clear exposure report with compliance status, control recommendations and a re-monitoring interval — defensible evidence for HSE, insurers and auditors.

Frequently asked questions

What is the NO2 workplace exposure limit?

Nitrogen dioxide has an 8-hour TWA of 0.5 ppm and a 15-minute STEL of 1 ppm under EH40.

Where does workplace NO2 come from?

Combustion processes, diesel engine exhaust, welding and some acid-related chemical processes.

How is NO2 measured?

By direct-reading electrochemical sensors for real-time data and by sorbent sampling where a time-weighted average is required.