Hi, it’s Chris. This is just a guide, not legal or compliant. DYOR. This is literally just for me to have access to rough data for when I am calibrating and benchmarking the chalk dust in the air at my local climbing gym. This is just my collection of tables dragged off the internet, or summarised – and not the sourced data. Read that? this is NOT all sourced data and triple checked.
Why do I care about this? I climb at my local climbing gym 3 times a week, and on site for 3 hours or so each time. As a family we all climb, and as 2/3 kids have asthma, and so does my wife – I wanted to try and track the air quality.
I’m building a dedicated air quality sensor that’ll sit running in the climbing gym for a few weeks so I can get my own data.
I do appreciate that ‘overall’ particulate levels don’t show the full picture, and i’ll probably have to make a ‘wearable’ IAQ sensor too, as I guess that 95% of chalk exposure happens when I’m dipping my hands into my chalk bag and actually climbing, rather than the ambient levels in the air.
However the staff sitting at the desk, or just ‘in house’ are just breathing the ambient – so it’s all relevant.
Thanks,
Chris.
1. WHO guideline levels for PM2.5 and PM10
| Pollutant | Averaging period | WHO 2021 air quality guideline |
|---|---|---|
| PM2.5 | Annual mean | 5 µg/m³ |
| PM2.5 | 24-hour mean | 15 µg/m³ |
| PM10 | Annual mean | 15 µg/m³ |
| PM10 | 24-hour mean | 45 µg/m³ |
Note: WHO guideline levels are health-based guidance. They are not UK workplace legal exposure limits.
2. WHO interim targets for particulate matter
| Pollutant | Averaging period | Interim target 1 | Interim target 2 | Interim target 3 | Interim target 4 | WHO guideline |
|---|---|---|---|---|---|---|
| PM2.5 | Annual mean | 35 µg/m³ | 25 µg/m³ | 15 µg/m³ | 10 µg/m³ | 5 µg/m³ |
| PM2.5 | 24-hour mean | 75 µg/m³ | 50 µg/m³ | 37.5 µg/m³ | 25 µg/m³ | 15 µg/m³ |
| PM10 | Annual mean | 70 µg/m³ | 50 µg/m³ | 30 µg/m³ | 20 µg/m³ | 15 µg/m³ |
| PM10 | 24-hour mean | 150 µg/m³ | 100 µg/m³ | 75 µg/m³ | 50 µg/m³ | 45 µg/m³ |
3. UK ambient air legal / policy context
| Pollutant | Averaging period | UK / England value | What it means |
|---|---|---|---|
| PM2.5 | Annual mean | 20 µg/m³ | UK ambient air limit value, stage 2, in force from 1 January 2020 |
| PM10 | Annual mean | 40 µg/m³ | UK ambient air limit value |
| PM10 | 24-hour mean | 50 µg/m³, with 35 permitted exceedances per year | UK ambient air limit value |
| PM2.5 | Annual mean | 10 µg/m³ by 2040 | England statutory target |
| PM2.5 | Population exposure | 35% reduction by 2040 compared with 2018 | England population exposure reduction target |
Note: these are outdoor/ambient air standards and policy targets. They are not workplace dust exposure limits.
4. UK Daily Air Quality Index bands for PM2.5
| DAQI band | Index values | PM2.5 level |
|---|---|---|
| Low | 1–3 | 0–35 µg/m³ |
| Moderate | 4–6 | 36–53 µg/m³ |
| High | 7–9 | 54–70 µg/m³ |
| Very high | 10 | 71+ µg/m³ |
The DAQI PM2.5 band is based on a daily mean for historical data, or the latest 24-hour running mean for the current day.
5. UK Daily Air Quality Index bands for PM10
| DAQI band | Index values | PM10 level |
|---|---|---|
| Low | 1–3 | 0–50 µg/m³ |
| Moderate | 4–6 | 51–75 µg/m³ |
| High | 7–9 | 76–100 µg/m³ |
| Very high | 10 | 101+ µg/m³ |
The DAQI PM10 band is based on a daily mean for historical data, or the latest 24-hour running mean for the current day.
6. Workplace dust types and rough PM equivalents
| Workplace term | Rough PM equivalent | What it means | Where it tends to deposit |
|---|---|---|---|
| Inhalable dust | PM100-ish / total inhalable | Dust that can enter the nose or mouth | Nose, throat, upper airways; some may go deeper |
| Thoracic dust | PM10-ish | Dust that can pass beyond the larynx into the chest airways | Larger airways and lungs |
| Respirable dust | PM4-ish | Smaller dust that can reach the gas-exchange region of the lungs | Deep lungs / alveolar region |
| PM2.5 | Fine-particle subset of respirable dust | Fine airborne particles 2.5 µm and below | Can penetrate deep into the lungs and may enter the bloodstream |
| PM1.0 | Very fine particles | Fine particles 1 µm and below | Deep lung fraction |
Important: respirable dust is not the same as PM2.5. Respirable dust is closer to PM4. PM2.5 is a smaller fine-particle subset.
7. UK workplace dust trigger values under COSHH
| Workplace dust type | 8-hour time-weighted average | Same value in µg/m³ |
|---|---|---|
| Inhalable dust | 10 mg/m³ | 10,000 µg/m³ |
| Respirable dust | 4 mg/m³ | 4,000 µg/m³ |
These are workplace dust trigger values under COSHH. They are much higher than WHO ambient air health guidance because they are different systems measuring different things.
8. How an SPS30-style particle sensor maps to dust categories
| Sensor reading | Best use | Workplace / health interpretation |
|---|---|---|
| PM1.0 | Very fine particles | Useful for fine-particle patterns, but no simple UK workplace dust limit |
| PM2.5 | Fine-particle health risk | Best matched to WHO PM2.5 guidance |
| PM4.0 | Rough proxy for respirable dust | Closest useful consumer-sensor proxy for respirable dust |
| PM10 | Coarse chalk cloud / larger airborne particles | Useful for spotting chalk-dust events, but not the same as inhalable dust |
| Inhalable dust | Not properly measured by this type of PM sensor | Requires occupational dust sampling |
A sensor like this can show when chalk dust is high, when it peaks, and how quickly it clears. It cannot prove legal workplace compliance.
9. Where climbing chalk dust sits
| Chalk dust fraction | Likely sensor signal | Interpretation |
|---|---|---|
| Visible chalk cloud | Mostly PM10 and larger inhalable dust | Obvious airborne chalk; likely to affect the room and upper airways |
| Fine suspended chalk | PM4 and below | More relevant to respirable dust exposure |
| Deep-lung fine fraction | PM2.5 and PM1.0 | More relevant to fine-particle health concern |
| Total chalk dust breathed in by staff | Not captured fully by PM2.5/PM10 sensor | Needs occupational inhalable/respirable dust sampling |
10. WHO-style exposure table for PM2.5 and PM10
This table estimates how long someone could be in a constant concentration before using up a 24-hour WHO guideline “budget”.
Formula used:
PM2.5 maximum hours ≈ 15 × 24 ÷ measured PM2.5
PM10 maximum hours ≈ 45 × 24 ÷ measured PM10
This is a simplified comparison only. It assumes the rest of the day has zero additional exposure, which is unrealistic.
| Constant level | Max time before WHO PM2.5 24-hour guideline is exceeded | Max time before WHO PM10 24-hour guideline is exceeded |
|---|---|---|
| 15 µg/m³ | Full 24h within guideline | Full 24h within guideline |
| 25 µg/m³ | 14 h 24 min | Full 24h within guideline |
| 45 µg/m³ | 8 hours | Full 24h within guideline |
| 50 µg/m³ | 7 h 12 min | 21 h 36 min |
| 100 µg/m³ | 3 h 36 min | 10 h 48 min |
| 250 µg/m³ | 1 h 26 min | 4 h 19 min |
| 500 µg/m³ | 43 min | 2 h 10 min |
| 1,000 µg/m³ | 22 min | 1 h 5 min |
Example: if a climbing gym sits at PM2.5 = 45 µg/m³, then an 8-hour shift would use up the WHO 24-hour PM2.5 guideline, even before considering the rest of the person’s day.
11. UK workplace dust exposure table
This table uses the UK COSHH trigger values for general dust:
Respirable dust: 4,000 µg/m³ as an 8-hour time-weighted average
Inhalable dust: 10,000 µg/m³ as an 8-hour time-weighted average
Formula used:
Respirable dust maximum hours ≈ 4,000 × 8 ÷ measured respirable dust
Inhalable dust maximum hours ≈ 10,000 × 8 ÷ measured inhalable dust
| Constant level | Respirable dust / PM4 proxy: max time before 4,000 µg/m³ 8h TWA | Inhalable dust: max time before 10,000 µg/m³ 8h TWA |
|---|---|---|
| 500 µg/m³ | Full 8h shift within trigger value | Full 8h shift within trigger value |
| 1,000 µg/m³ | Full 8h shift within trigger value | Full 8h shift within trigger value |
| 2,000 µg/m³ | Full 8h shift within trigger value | Full 8h shift within trigger value |
| 4,000 µg/m³ | 8 hours | Full 8h shift within trigger value |
| 8,000 µg/m³ | 4 hours | Full 8h shift within trigger value |
| 10,000 µg/m³ | 3 h 12 min | 8 hours |
| 20,000 µg/m³ | 1 h 36 min | 4 hours |
Important: PM4 from a consumer sensor is only a rough proxy for respirable dust. Inhalable dust is not properly measured by an SPS30-style sensor.
12. Practical dashboard table for a climbing gym
| Dashboard panel | What it shows | Useful thresholds / notes |
|---|---|---|
| PM2.5 live | Fine-particle spikes | Useful for immediate exposure peaks |
| PM2.5 24-hour rolling average | Health-guidance comparison | Show 5 µg/m³ and 15 µg/m³ lines |
| PM10 live | Chalk-cloud events | Useful for visible/coarse chalk dust |
| PM10 24-hour rolling average | Daily coarse-particle exposure | Show 15 µg/m³ and 45 µg/m³ lines |
| PM4 8-hour rolling average | Rough respirable dust proxy | Show 4,000 µg/m³, labelled “not compliance-grade” |
| PM10 / PM2.5 ratio | Whether dust is mainly coarse chalk | High ratio suggests coarse chalk-dust dominance |
| Ventilation recovery time | How quickly dust clears after busy periods | Useful for assessing cleaning, ventilation and occupancy patterns |
A low-cost particle sensor can be very useful for seeing when climbing chalk dust rises, how long it stays in the air, and whether ventilation clears it quickly. However, it should be treated as a screening tool, not as legal workplace exposure evidence.
WHO PM2.5 and PM10 guidelines are useful health-based benchmarks, especially for understanding fine-particle exposure. UK workplace dust limits use different occupational categories: inhalable dust and respirable dust, measured as 8-hour time-weighted averages. Proper workplace compliance assessment normally requires appropriate occupational dust sampling, often including personal sampling of the air workers actually breathe during a shift.
In short: a PM sensor can show whether there is a likely dust problem. It cannot, on its own, prove whether a workplace is compliant.