A diesel van is run inside for a diagnostic test. The roller door is open, but the air is still and workers nearby can smell exhaust. That is not evidence of adequate control. Diesel engine exhaust emissions are a process-generated COSHH hazard: the employer must understand where exposure occurs, prevent or reduce it, use effective engineering controls and check that the real working method matches the assessment.
Find every source, not just the workshop test bay
Diesel exhaust exposure can arise in vehicle workshops, inspection pits, warehouses, loading areas, depots, construction sites and enclosed yards. Sources include vans and lorries, forklifts, generators, compressors and mobile plant. Cold starts, intermittent testing, long idling periods, blue or black smoke and work in enclosed or poorly ventilated spaces deserve particular attention.
The COSHH assessment should follow the work through a normal shift. Record which engines run, where they run, for how long, how often and who is nearby. Include visiting drivers, contractors, cleaners and office staff whose air intake or doorway is close to an exhaust discharge. Check night work and winter practice, when doors that were open during the assessment may be closed.
Do not wait for visible smoke. HSE says vehicle exhaust can irritate the eyes and respiratory tract, while carbon-fuelled engine fumes contain carbon monoxide. Long-term repeated exposure to diesel fumes can increase lung-cancer risk. Smell and smoke can reveal poor control, but their absence does not prove the air is safe.
HSE: diesel engine exhaust emissions at work ↗ · Related guide: COSHH assessment versus a safety data sheet →
Prevent and reduce engine running first
Start with elimination. Can the test be completed electronically, outside or on a properly designed external bay? Can goods be moved with electric equipment? Can delivery vehicles switch off while waiting? Can a generator be placed outside with its exhaust directed away from people, doors, windows and air intakes? The safest exposure is the one that is not created.
Where running is necessary, reduce the duration and the number of people exposed. Use a defined test position, prohibit casual idling, keep uninvolved workers out of the area and plan vehicle movements so fumes do not accumulate around loading staff. A short task repeated throughout the day may create a different exposure pattern from one longer test.
Engine maintenance matters, but a modern or well-maintained vehicle is not permission to run indoors without control. HSE warns that catalytic converters are less effective when exhaust gases are cool and do not remove toxic oxides of nitrogen. Treat cleaner technology as helpful reduction, not as a replacement for the assessment.
HSE: vehicle exhaust emissions ↗ · Related guide: workplace transport risk assessment →
Capture stationary exhaust at the tailpipe
Where vehicles must run indoors, HSE advises connecting an exhaust-gas scavenging system to the tailpipe, particularly for work in an inspection pit. Capture at source before fumes disperse through the workshop. The system must suit the exhaust temperature, flow, tailpipe arrangement and range of vehicles actually handled.
Discharge to a safe outdoor location where fumes cannot be drawn back through doors, windows or ventilation intakes and will not expose neighbours or people using an adjacent walkway. Maintain hoses, couplings and flexible connections so leaks do not move the exposure from the tailpipe to the operator's breathing zone.
Write the control into the job: connect before static running, confirm extraction is operating, stop the engine if the hose detaches or the system fails, and disconnect only when the engine is off. A system mounted on the wall but bypassed for quick jobs is not effective control.
HSE COSHH Essentials SR14 and SR15 ↗ · Related guide: local exhaust ventilation →
Check the assessment, extraction and working method together.
HR + SAFETY can help North East workshops, depots and SMEs review diesel-exhaust sources, task controls, maintenance evidence and the actions needed where exposure is uncertain.
Discuss a diesel-exhaust reviewGeneral ventilation supports source control—it does not replace it
Fresh-air ventilation should remove residual contamination and prevent accumulation from moving vehicles and other sources that cannot be connected to tailpipe extraction. Assess the whole occupied zone, including pits, mezzanines, adjoining rooms and low-air-movement corners. Air should move from clean areas towards contaminated areas and discharge safely.
Do not record ‘roller door open’ as the only control. HSE specifically warns against relying on access doors because they may be closed in winter. Wind direction and still air also make natural ventilation unreliable. Mechanical ventilation needs a clear design purpose, maintenance arrangement and indication of failure where loss of performance would leave people exposed.
Carbon-monoxide or air-quality monitoring may provide useful warning or evidence, but an alarm is not a substitute for preventing emissions and capturing them at source. Set any alarm response in advance: stop engines, evacuate or restrict the area, ventilate safely, investigate the cause and do not resume ordinary work until controls are restored.
Inspect, maintain and verify the controls
Give operators simple pre-use checks: hose condition, secure connection, visible damage, airflow indication and safe discharge. Record defects and prevent use where effective capture is doubtful. Planned maintenance should follow the manufacturer's information and the conditions of use, including heat, crushing, chemical contamination and repeated vehicle contact.
Where the scavenging system is local exhaust ventilation, COSHH requirements for maintenance, thorough examination and testing apply. The normal maximum interval for LEV examination is 14 months, but risk, deterioration or specialist advice may justify shorter intervals. The report should confirm whether the system still controls the real task, not simply that a fan runs.
Exposure measurement may be needed where the assessment cannot demonstrate adequate control, work varies materially, complaints or symptoms arise, or changes alter the exposure pattern. Use competent occupational-hygiene advice and set the monitoring question first. HSE explains that exposure monitoring is evidence about control; it does not replace the control measures.
HSE: workplace exposure limits and monitoring ↗ · COSHH regulation 9: maintenance and examination ↗
Diesel-exhaust control checklist
Legal requirements and official guidance were checked on 27 October 2026. HSG187 and the HSE COSHH Essentials sheets are practical guidance, not certificates or substitutes for the employer's task-specific assessment. Use them to define proportionate controls, then verify those controls in the workplace.
- List every diesel engine, location, task, duration and group of people who may be exposed.
- Observe cold starts, intermittent tests, idling, enclosed areas and winter working conditions.
- Move avoidable engine running outside or replace the source where reasonably practicable.
- Connect suitable tailpipe extraction whenever stationary vehicles run indoors.
- Discharge fumes where they cannot re-enter or expose other people.
- Maintain hoses, couplings, fans, indicators and general ventilation.
- Train workers to stop the task if extraction disconnects, fails or cannot be used.
- Investigate blue or black smoke, complaints, symptoms and control failures promptly.
- Arrange competent examination and exposure measurement where the evidence requires it.
- Review the COSHH assessment after layout, vehicle, process or ventilation changes and after incidents or adverse findings.
Control diesel exhaust in the order that works: prevent unnecessary emissions, reduce running time and exposed people, capture stationary exhaust at the tailpipe, provide effective supporting ventilation, maintain the system and verify performance against the real task.
This guide provides general information for UK employers. It is not legal advice and should not replace advice based on the facts of a specific matter.