Official UK Statutory & Health Thresholds
Radiation protection bodies across the UK and Europe evaluate indoor radon according to standardized statistical concentration tiers:
• Outdoor Baseline (4 Bq/m³): The natural concentration of radon in open outdoor air in Great Britain.
• UK Household Average (20 Bq/m³): The typical baseline found in homes in low-risk sedimentary areas like London and East Anglia.
• UK Target Level (100 Bq/m³): Introduced by the UKHSA to provide an ambitious safety goal. When remediation systems (such as sumps or positive ventilation) are installed, contractors aim to reduce radon below this 100 Bq/m³ threshold.
• UK Action Level (200 Bq/m³): The official public health threshold. If a home exceeds 200 Bq/m³, homeowners are advised to take active steps to reduce concentrations.
• UK Workplace Action Level (300 Bq/m³): Under the Health and Safety at Work etc. Act 1974 and the Ionising Radiations Regulations 2017 (IRR17), employers must carry out risk assessments and remediate commercial spaces or basements exceeding 300 Bq/m³.
| Radon Level (Bq/m³) | Status Classification | Health Interpretation | Recommended Response |
|---|---|---|---|
| 0 to 50 Bq/m³ | Low / Baseline | Standard background radiation | No action needed |
| 51 to 99 Bq/m³ | Moderate / Safe | Well below Action Level | No action needed |
| 100 to 199 Bq/m³ | Target Level Zone | Elevated for smokers or high-risk occupants | Consider low-cost ventilation improvements |
| 200 to 499 Bq/m³ | Above Action Level | Significant cumulative radiation exposure | Install active PIV fan or sub-floor sump |
| 500+ Bq/m³ | Critically Elevated | Urgent public health hazard | Install high-performance radon extraction immediately |
Comparison: UK vs WHO International Standards
The World Health Organization (WHO) recommends an international reference level of 100 Bq/m³. However, the WHO acknowledges that if this cannot be implemented due to prevailing country-specific geological factors, the reference level should not exceed 300 Bq/m³.
The UK's dual threshold (Target Level 100 Bq/m³, Action Level 200 Bq/m³) aligns closely with WHO international best practice.