Indoor Air Pollutants
Airflow & IAQ · Airflow & IAQ overview
Indoor air pollutants are the airborne substances that affect the quality of the air people breathe inside workplaces. They range from low-level comfort nuisances to substances with established health effects and workplace exposure limits. Understanding which pollutants are present, where they come from and how they move is the foundation of any credible indoor air quality programme.
What indoor air pollutants are
Indoor air pollutants include particulates of various size fractions, gases and vapours, biological aerosols and complex mixtures from combustion or process activity. The same pollutant can be a comfort issue at low concentration and a health hazard at higher exposure, which is why context — concentration, exposure duration and who is exposed — matters as much as the substance itself.
In a workplace setting, pollutants are assessed against HSE Workplace Exposure Limits (WELs) in EH40 where they apply, and against general indoor environment guidance such as CIBSE TM40 and BS EN 16798 for offices and similar spaces.
Common workplace sources
Sources fall into three broad groups: building-related, occupant-related and process-related. A useful pollutant assessment identifies which group each significant source belongs to, because the control options differ.
- Building-related: furnishings, sealants, paints, flooring adhesives, mould growth in damp fabric.
- Occupant-related: CO₂ from respiration, personal care products, cooking, cleaning chemicals.
- Process-related: dust from machining or handling, welding and soldering fume, solvent vapour, mists from coolants, combustion products from vehicles or heaters.
- External: traffic-derived NO₂ and particulates drawn in through poorly located intakes, neighbouring industrial emissions.
- Drainage and waste: hydrogen sulphide and other gases from disused traps, drains and waste handling areas.
- Stored materials: solvents, fuels, cleaning agents and chemicals releasing vapour in stores and plant rooms.
Comfort, nuisance and hazardous contaminants
Not all indoor air pollutants are equal. A reasonable assessment separates low-level comfort issues — minor odours, mild stuffiness — from nuisance contaminants that affect productivity and complaint rates, and from hazardous airborne contaminants with documented health effects and exposure limits.
Confusing these categories causes two failure modes: treating a genuine hazard as a comfort issue and under-controlling it, or treating a comfort complaint as a hazard and committing disproportionate resources. Clear classification at the start of an investigation prevents both.
Pollutant pathways and ventilation
Concentration depends on the balance between emission rate and removal rate. Removal in indoor air is dominated by ventilation — both general dilution and local extraction at source. Pathway analysis follows the contaminant from its source, through the air, to the breathing zone of the people affected.
Pressure relationships between zones, transfer paths through doors and ceiling voids, recirculation in air handling units, and seasonal variation in ventilation rate all change pollutant pathways. A static one-day measurement may miss pathways that only open up under certain conditions, which is why investigation usually combines instantaneous measurement with longer-term logging and observational review.
Why source control and ventilation both matter
The COSHH hierarchy of control is explicit: eliminate the source where possible, then control at source with extraction, then dilute with general ventilation, then administrative measures, then PPE as a last resort. Indoor air pollutant management follows the same logic.
Ventilation alone cannot economically control a pollutant generated continuously at high rate; source control alone cannot manage transient or distributed emissions. The right answer for most workplaces is a combination — reducing emission at source where feasible, capturing what remains at the point of release, and using general ventilation to manage residual concentrations and provide fresh outdoor air to occupants.
Frequently asked questions
Are office buildings affected by indoor air pollutants?
Yes. Offices typically have lower source strengths than industrial spaces, but VOCs from furnishings and cleaning, particulates from outdoor air, elevated CO₂ from under-ventilated meeting rooms, and printer emissions all show up in office IAQ investigations.
How are pollutants measured?
Through a combination of real-time instruments (particulate counters, photoionisation detectors for VOCs, CO₂ monitors), pumped sorbent tube sampling for specific substances analysed in a laboratory, and longer-term data loggers. The method depends on which pollutant is being assessed and to what benchmark.
Can ventilation upgrades fix every pollutant problem?
No. Ventilation manages concentration and removal, but where the source is strong, intermittent or hazardous, controlling the source itself is usually more effective. Ventilation and source control are complementary, not interchangeable.
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