Indoor Particulate Investigation
Independent indoor air quality assessors · Since 1999
An indoor particulate investigation is used when monitoring shows high readings, peaks appear without an obvious activity or conditions remain unexplained after routine checks. The aim is source apportionment: testing which indoor activity, outdoor pathway, ventilation route or material best fits the evidence. We combine time patterns, indoor-outdoor relationships, activity logs, location mapping, filter and bypass checks, and sample analysis where justified. The outcome ranks supported sources and defines the next action rather than attaching a cause to one monitor peak.
Established 1999 · 2,500+ assessments · SafeContractor approved · BOHS Affiliate Member · London & South East
When routine PM monitoring is no longer enough
Routine monitoring can show whether PM2.5 or PM10 changes by room and time. Investigation begins when those patterns conflict, persist after simple actions or need a defensible source explanation. Triggers include recurring peaks, unusual filter loading, differences between nominally similar zones, suspected outdoor ingress or readings linked imperfectly to cleaning, printing, deliveries or works. We review existing data before adding instruments so the next campaign tests hypotheses rather than merely collecting more of the same.
Building a source-apportionment plan
The plan sets out plausible sources and the evidence each would produce. An outdoor source may create related movement at an intake and internal zones after a time delay. A local activity may produce a sharp peak confined to nearby rooms. Filter bypass can create a distribution aligned with one air-handling system. Resuspension may follow occupancy or cleaning. Monitor positions, logging periods and sample choices are then selected to distinguish those patterns.
Time patterns and activity logs
Real-time optical monitors are synchronised across affected, comparison and pathway locations. Occupancy, cleaning, plant schedules, windows, deliveries, maintenance and unusual events are logged. We examine onset, duration, particle-fraction relationship and movement between points. Correlation is treated as evidence, not proof: repeated alignment strengthens a hypothesis, while contradictions guide the next check. The report retains events that do not fit the preferred explanation.
Indoor-outdoor ratios and pathways
A suitable outdoor or intake monitor can show whether indoor changes track external conditions. Ratios are interpreted with ventilation mode, window use, pressure relationships, weather and monitor response. We also inspect doors, loading areas, penetrations and other plausible ingress routes. A high indoor-to-outdoor relationship does not automatically mean an indoor source, because timing and filtration affect both values; the complete pattern matters.
Filter efficiency, sealing and bypass checks
Accessible filter type, installation, loading, damage, seals and housing condition are recorded. We look for visible paths around the filter and compare zones served by different systems. These observations can support an air-distribution hypothesis but do not replace engineering tests or mechanical diagnosis. Where defects are suspected, the HVAC contractor confirms specification, performance and corrective work. Follow-up monitoring can test whether occupied-space particulate patterns changed afterward.
Sample analysis and evidential weight
Collected airborne or deposited material may be analysed when composition can separate hypotheses. The analytical route is chosen for the suspected material rather than applied generically. Results are integrated with timing, location and pathways because finding a component does not prove where it entered. Each source conclusion is described by confidence, conflicting observations and remaining uncertainty, giving the client a proportionate basis for action.
Investigation outcomes
The action plan may recommend source control, containment, cleaning review, filtration correction, intake management, targeted occupational sampling or construction controls. It identifies which discipline owns each next step. Repeat monitoring uses comparable locations and conditions to test improvement. If evidence remains inconclusive, the report proposes a narrower follow-up instead of overstating certainty.
Is this the right page?
Choose Indoor Particulate Investigation when levels are already elevated or unexplained and source attribution is needed. PM2.5 and PM10 Office Monitoring provides routine trend evidence. Dust Complaint Investigation addresses a broader active complaint that may include deposits and interviews.
Limitations and what this assessment cannot tell you
Source apportionment combines several evidence lines and may retain uncertainty.
- Association in time does not establish causation on its own
- Optical PM data does not identify chemical composition
- Outdoor comparison depends on representative placement and weather context
- Accessible filter observations cannot confirm full mechanical performance
- Some hypotheses require substance-specific or occupational sampling outside the initial scope
What the investigation report includes
- Existing evidence and ranked source hypotheses
- Monitor network, activity records and operating context
- Time-pattern and indoor-outdoor analysis
- Filter, bypass and pathway observations
- Laboratory findings where targeted samples were commissioned
- Confidence-rated conclusions and staged next actions
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