Quick answer
Identify how fresh air reaches each occupied area and whether the arrangement works for the activity and occupancy. Act on poor ventilation, maintain systems and obtain competent advice where needed. General fresh-air assessment does not replace controls for hazardous process fumes or dust.
Why air movement is not the same as fresh-air supply
A desk fan moves existing air but does not by itself supply outdoor air. HSE’s ventilation-assessment guidance advises identifying occupied areas with poor ventilation and considering how fresh air is provided.
Include staff rooms, changing areas and smaller occupied rooms, not only the main production or customer space. Review actual use and occupancy rather than the building’s original description.
Make a simple occupied-area register
| Record | What to establish |
|---|---|
| Area and activity | Who uses it, when and for what work? |
| Fresh-air route | What windows, vents or mechanical supply provide outdoor air? |
| Evidence of performance | What is known about operation, complaints, checks or suitable monitoring? |
| Constraints | Are temperature, security, noise, outdoor contamination or fire precautions relevant? |
| Action and ownership | Who will investigate, improve, maintain and verify the arrangement? |
Improve the actual supply and maintain its operation
HSE’s improvement guidance covers natural and mechanical options and the need to understand what a system supplies. Do not assume an air-conditioning unit brings in fresh air simply because it cools the room.
Keep suitable inlets and vents functional and arrange competent maintenance. Any change must also respect fire precautions and other risks: propping a required fire door open is not a suitable ventilation solution.
The workplace welfare ACOP gives the GB regulatory guidance. Complex systems or uncertain performance may need a ventilation engineer.
Use CO2 monitoring as an aid, with the right interpretation
HSE’s CO2-monitor guidance explains representative placement and when monitoring can help identify poor ventilation. Read and interpret measurements with occupancy and the suitability of the space in mind.
A single reading is not a universal declaration that air is safe. Do not use general occupancy-related CO2 monitoring as clearance for hazardous chemical releases, combustion gases or cooking fumes. Those hazards need appropriate assessment and control.
Example: review a room after occupancy increases
A small staff room begins hosting longer team sessions with more people. The manager checks the existing fresh-air provision, how the room is used and whether the system is operating as intended. Suitable evidence and competent advice inform the improvement.
The action record identifies who maintains the arrangement and how its effect will be checked. Moving a portable fan into the room would not answer the fresh-air question.
NI employers should use the NI workplace framework and HSENI guidance for the applicable duties.
Next steps
List the occupied areas and fresh-air arrangements, investigate uncertain or poor performance and assign improvements. Keep general ventilation separate from the specialist controls required for particular workplace substances or processes.
Use HSE’s ventilation-assessment guidance — Fresh-air performance and system changes require evidence and suitable competence, with specialist extraction assessed separately.