Radon in workplaces

Origin, exposure and health effects

• Origin. Radioactive noble gas from the uranium decay chain in the ground; its concentration depends on the geology, soil permeability, building construction and ventilation.
• Entry points. Cracks and joints in slabs and walls in contact with the ground, installation passages, drains, basements and, to a lesser extent, construction materials and well water.
• Affected workplaces. Ground floors and basements of any activity in high potential areas, mines and tunnels, caves and tourist galleries, spas and resorts with groundwater, water treatment plants and underground parking lots.
• Health effects. Inhalation of radon and its decay products, which are deposited in the lungs and emit alpha radiation; it is the second leading cause of lung cancer and increases the risk in smokers.
• Reference level. 300 becquerels per cubic meter of average annual concentration, value from which corrective measures must be adopted.
• Variability. The concentration varies throughout the day and year, so measurements must be long-term and planned to estimate the annual average under the applicable periods and conditions.

Obligations of Royal Decree 1029/2022 and Instruction IS-47

The regulations require those responsible for workplaces on ground or below-ground floors within priority municipalities, and for work activities with a risk of radon exposure (such as those carried out in underground facilities, spas, and water treatment plants), to have radon concentration measurements in the air taken by accredited laboratories, to integrate the results into the occupational risk assessment, to inform and consult with workers, and to implement measures to reduce the concentration below the reference level of 300 becquerels per cubic meter. Where zones accessible to workers have an annual average above 300 becquerels per cubic meter, the declaration is submitted to the competent authority of the autonomous community under Article 103 of Royal Decree 1217/2024, except for the facilities exempted by that article. Where no area occupied by workers exceeds an annual average of 1,000 becquerels per cubic meter, the deadline is one year from the date of the measurement report. If construction or mechanical corrective measures are implemented within that period, it is extended by one year from their completion; no declaration is required if subsequent measurements do not exceed 300 becquerels per cubic meter. If any occupied area exceeds 1,000, the deadline is one month from the report, regardless of whether corrective measures have begun.

Before submitting the declaration, the operator must have commissioned the design and implementation of corrective measures from a UTPR or SPR authorised for natural radiation. Its report, including dose estimates before and after the measures, must be submitted to the Nuclear Safety Council within one month of issue. If the reference level remains exceeded, concentrations must be reassessed and doses estimated under Article 19 of Royal Decree 1029/2022. Classification as a worker exposed to radon and the designation of radon areas depend on the potential to exceed 6 millisieverts per calendar year. In that case, Article 104 of Royal Decree 1217/2024 requires a dose monitoring programme with advice from a UTPR, to be submitted to the Council within six months of receipt of the previous report.

The Nuclear Safety Council’s Instruction IS-47, published in 2025, approves the list of priority action municipalities (those classified as zone II in appendix B of section HS 6 of the Technical Building Code) and establishes the measurement guidelines in workplaces located on ground floors and basements of those municipalities: measurement for at least three months between October and May, or for a calendar year in quarterly periods, with a number of detectors proportional to the surface area and the distribution of the premises, a maximum period of six months after the opening of the center to start the measurements, and updating studies every five years; the ten-year interval applies only when active systems are not needed to keep levels below the reference level and none of the measurements in the latest update exceeds 300 becquerels per cubic meter. Following changes capable of significantly affecting concentration, new measurements must begin within six months of completion.

Corrective and preventive measures

• Ventilation. Increase in natural or mechanical ventilation of the affected premises, with pressurization where possible.
• Sealing. Sealing of cracks, joints, installation passages and drains in slabs and walls in contact with the ground.
• Ground depressurization. Extraction systems under the slab or in sanitary chambers that evacuate radon before it enters the building.
• Barriers and design. Radon-resistant membranes and ventilated chambers in new construction and renovation in accordance with the Technical Building Code.
• Organization. Limiting the time spent in the most affected premises, relocating workstations and prohibiting smoking.
• Verification. Subsequent measurements to check the effectiveness of the measures and maintenance of the ventilation and extraction systems.

Organizational application: how to manage radon in the workplace

1. Check if the workplaces are located in municipalities of priority action according to Instruction IS-47 or if they carry out activities with a risk of exposure to radon, and identify the premises on ground floors and basements.
2. Within the scope of IS-47, begin detector exposure within six months after opening or resuming activity without a valid survey, using an accredited laboratory and appropriate distribution and duration, unless the conditional exemption under Article 5.2 applies.
3. Integrate the results into the occupational risk assessment, inform and consult with workers and their representatives, and keep the documentation.
4. Apply corrective measures when the reference level is exceeded (ventilation, sealing, depressurization, reorganization) and repeat measurements to verify their effectiveness.
5. Where required, submit the declaration to the autonomous community and the reports to the Nuclear Safety Council within the deadlines of Article 103 of Royal Decree 1217/2024. If the exceedance persists, reassess concentrations and doses; apply the specific classification and monitoring requirements where doses may exceed 6 millisieverts per year.
6. Update studies every five years, or every ten only when active systems are not needed to keep levels below the reference level and none of the measurements in the latest update exceeds 300 becquerels per cubic meter. Begin reassessment within six months after changes capable of significantly affecting concentration.
7. Incorporate radon prevention into the design and rehabilitation of buildings in accordance with the Technical Building Code.

Preventive management software with those verified functions can maintain the inventory of centers and premises subject to measurement, record laboratory results and corrective measures, schedule verification measurements and periodic updates with expiration notices, document information and consultation with workers, and maintain the traceability required by the regulations.

Limits and common mistakes

1. Assuming that radon only affects mines and tunnels and not checking the situation of centers in priority action municipalities.
2. Performing short-term measurements or measurements outside of the indicated periods, which do not represent the average annual concentration.
3. Measure only in some rooms and forget about basements, archives, warehouses and changing rooms on the ground floor.
4. Not integrating the results into the risk assessment or informing the workers.
5. Apply corrective measures without verifying their effectiveness with new measurements or maintaining ventilation systems.
6. Do not update studies after works that affect the building envelope or ventilation.

Specific requirements depend on the location of the center, the activity, and the current guidelines of the Nuclear Safety Council; this sheet is for informational purposes only.

Regulatory and reference framework

• Royal Decree 1029/2022, of December 20. Regulation on the protection of health against the risks arising from exposure to ionizing radiation; radon in workplaces.
• Royal Decree 1217/2024, of 3 December. Articles 103 and 104: declarations, additional studies and radon dose monitoring.
• Instruction IS-47, of April 9, 2025, from the Nuclear Safety Council . List of municipalities with priority action against radon and guidelines for measurements in workplaces.
• Directive 2013/59/Euratom . Basic safety standards for protection against the dangers arising from exposure to ionizing radiation.
• Law 31/1995, of November 8. Law on the Prevention of Occupational Risks.
• Royal Decree 39/1997, of January 17. Regulation of Prevention Services; risk assessment.
• Nuclear Safety Council . Regulatory body for radiological protection; information on radon.

Section HS 6 of the Technical Building Code establishes the requirements for protection against radon in new buildings and in interventions in existing buildings, and its appendix B classifies the municipalities by zones.

From a building inventory to a representative survey

The first decision is not to purchase a detector, but to establish which areas and activities require assessment. Article 75 of Spain’s Royal Decree 1029/2022 includes underground workplaces, activities processing or using groundwater, and ground or below-ground floors in priority municipalities. An archive, changing room or technical room may be relevant even without a fixed workstation. Areas occupied or accessed for work should be considered, subject to the exclusions and criteria applicable to the survey.

A postal address and radon potential map help identify obligations but do not predict the concentration in a particular room. Nearby buildings may differ in ground contact, cracks, services, ventilation and use. The inventory should represent floors, sampling zones, occupancy and existing radon protection systems. Where several employers share a property, they need to coordinate building information and measures affecting their workers rather than assume that surveying one office covers every space. The scope should remain clear in the resulting report.

Instruction IS-47 sets criteria for planning detector distribution and exposure within its scope. Ordinary occupancy and the intended operation of protective systems should be maintained; artificially changing ventilation only during the campaign distorts results. Each detector’s identifier, location and installation and removal dates allow the report to be interpreted. Moving a device between rooms without recording it may break the relationship between the result and the sampling zone. Staff should know why the equipment must remain undisturbed.

Long-term measurement estimates an annual average rather than capturing a favourable hour. The option of at least three months between October and May and the alternative of a year using periods no longer than a quarter must follow the instruction’s conditions. For underground facilities, the CSN recommends covering a full year. Criteria should not be transferred mechanically from a dwelling to a mine or from an ordinary building to an activity with special conditions.

Continuous monitors, personal detectors and wearable devices

A passive detector integrates exposure over its placement period and is processed under the measurement system. A continuous monitor provides a time series that may show changes associated with ventilation, occupancy or equipment operation. These tools serve complementary purposes. Selection depends on the technical question, metrological quality and applicable requirements; a numerical display does not itself demonstrate that the required annual average has been estimated correctly. A device should be chosen for a defined measurement task, not for its connectivity alone.

Portable or body-worn devices may be useful within a programme designed for the specific exposure, but not every wristband, general dosimeter or environmental sensor measures radon. The quantity detected, range, response, calibration and limitations must be checked. An external-radiation instrument does not become a measure of internal exposure from radon and its progeny simply because it is worn on the body. Device format and connection to an application do not replace that technical verification or the necessary assessment.

Where dose estimation is needed, environmental concentration is related to exposure conditions and time spent in the area using radiation-protection criteria. Bq/m³ expresses activity per volume; mSv expresses effective dose. These units are not interchangeable, and one isolated reading cannot provide a reliable dose without the relevant factors and conditions. Dosimetry selection and follow-up belong within the applicable programme, with authorised advice where legislation requires it. Numerical conversion should not be left to an unexplained dashboard formula.

Continuous monitoring can help identify extraction failure or compare conditions before and after an adjustment, but an alert needs a defined response. Responsibilities, checks and restoration of control should be recorded. A brief peak does not automatically mean that the annual average is exceeded; a low reading does not establish that the entire earlier period was adequate. Instantaneous data complement the survey and should not be used to bypass the required long-term regulatory measurement.

Underground workplaces and groundwater: changing exposures

In tunnels, mines, caves or galleries, geology and ventilation can vary along the route and over time. Assessment should represent working areas, access routes and maintenance tasks as well as the time spent by each group. A measurement near the entrance does not necessarily describe an interior working face. When excavation, ventilation arrangements or shifts change, the continuing representativeness of detector distribution and measurement periods should be checked. A previously valid survey may no longer describe the same conditions.

In facilities using groundwater, radon release may be associated with particular process points and spaces. The inventory should identify where water is handled or used and how air is renewed, avoiding treating the entire building as one zone for convenience. A thermal spa and a water-treatment installation may require different strategies. Decisions should rely on knowledge of the installation and technical assessment, rather than the sector name alone. Relevant maintenance activities should be included even where their duration is intermittent.

Ventilation can interact with other hazards and with the relationship between radon and its progeny. An underground intervention should therefore not be designed solely to obtain a lower gas reading without reviewing overall exposure and working conditions. Dust, gases, temperature, equipment energy and safe access also need consideration. Specialist advice helps prevent a change intended to improve one factor from worsening another. A lower concentration and a lower effective dose should not be assumed to be identical conclusions in every situation.

Organisational measures, such as reducing occupancy time or relocating tasks, may contribute to optimisation where appropriate. They need to be real and traceable: a written timetable does not reduce exposure if activity continues in the area. Nor should the problem be silently transferred to maintenance staff or contractors. Coordination should identify who enters, what information they receive and how controls are verified throughout relevant periods of use. Temporary arrangements should have a review point and a responsible person.

Mitigation and survey renewal: conditions that change the interval

The solution should address entry routes and building behaviour. Sealing, ventilation, barriers and ground depressurisation have different functions and are not interchangeable without assessment. Installed equipment needs commissioning, maintenance and verification. Acceptance records should document protected areas, normal operation and failures that could affect performance. The presence of a fan alone does not establish an appropriate concentration or reduced dose. The employer should understand which ongoing operating conditions are necessary to maintain the improvement.

IS-47 allows survey updates every ten years only when active systems are not needed to keep levels below the reference level and none of the measurements in the most recent update exceeds 300 Bq/m³. In other cases, the interval is five years. Consequently, a low result achieved using an active system does not automatically qualify for the ten-year interval. This distinction should be reflected in planning and follow-up reminders rather than being lost when a report is marked complete.

Changes capable of significantly affecting concentration also require reassessment measurements to begin within six months after completion. It is not sufficient simply to wait for the next periodic deadline. Changes to the building envelope, ventilation or connection with the ground may trigger this review. The project record should inform the prevention lead so an energy-efficiency improvement or internal refurbishment does not leave the radon study outdated. Significant changes and their assessment should remain traceable.

For example, a basement reaches acceptable concentrations through permanent extraction. Closing the action should not mean filing the report and scheduling a ten-year update: it should include active-system maintenance, checks and the applicable interval. If later refurbishment alters airflow, the survey is reviewed because of that change. The example shows that follow-up depends on the conditions sustaining the result rather than only the final number. Technical performance and administrative scheduling need to remain connected.

Traceability of results, decisions and radiation protection

The report should link each result to its zone, period, method and relevant conditions. It should also identify uncertainty and incidents such as lost detectors, relocation or campaign interruptions. A spreadsheet retaining only the maximum value loses information needed to interpret and update the survey. Documentation is integrated into risk assessment and should be available to the recipients and authorities specified by the applicable rules, with an understandable explanation for workers. These legal requirements here refer to the Spanish framework.

The reference level of 300 Bq/m³ and dose criteria serve different purposes. Exceeding the annual-average reference level calls for reducing concentrations or exposure and reassessing under the applicable framework. Articles 103 and 104 of Royal Decree 1217/2024 also regulate declarations, studies and dose monitoring in their respective circumstances. The declaration deadline depends, among other things, on whether any occupied area exceeds 1,000 Bq/m³; it should not be replaced by a generic application alert that does not reflect those conditions.

Digital management can organise zones, reports, measures and maintenance tasks if the chosen tool has those verified functions. It does not automatically turn results into a valid radiation classification or replace the laboratory or authorised advice. The final check is whether it is clear what was measured, which decision followed, who must act and how effectiveness will be verified. Requesting measurements, carrying them out, receiving a report and confirming a correction’s effectiveness are different states and should remain separately recorded.