Radon at workplaces

It is the employer’s duty to have the radon concentration of the workplace measured in the following cases:

• in all workspaces that are located wholly or partly underground in the whole country.
• in areas where more than 10 per cent of the radon concentrations measured earlier exceeds the value of 300 Bq/m³. STUK maintains a list of such areas.
• at workplaces throughout the country if they are located on ridges or very air-permeable gravel or sand formations
• in an installation that distributes household water where the water does not derive solely from a body of surface water and has contact with indoor air.

Radon measurement is not usually needed at workplaces that are located on the second or upper floors. In these locations, the radon concentrations are generally low.

The radon concentration in air at the workplace is determined primarily using an alpha track detector (integrating measurement) that is kept at the workplace for a minimum of two months, preferably three months, between the beginning of September and the end of May. If work at the workplace generally takes place outside the measurement period, e.g. in summer, the radon measurement should also be made outside the measurement period. The alpha track detector indicates the long-term average radon concentration. After this, if necessary, time-associated variations in the radon concentration can be analyzed by a so-called continuous radon measurement. Radon concentration during working hours

A key point in radon control at workplaces is that a reliable measurement method is used when determining the radon concentration. Radon measurements can be ordered from STUK or from a company that uses a measurement method that is approved by STUK.

Radon measurement aims at determining workers’ exposure to radon so the measurement points at the workplace and the number of measurement detectors needed are chosen accordingly.

The workspace under each ventilation machine and the separate building are measured as follows:

A hall-like or similar open working space under each ventilation machine shall be measured as follows:

• Each workplace is measured with at least two detectors, unless the total area of the workplace is small (less than 100 m²).
• At least one measurement must be made in each separate building. If a building has several ventilation systems, measurements must be conducted separately for each area covered by a single ventilation unit.
• Radon measurement at workplace is conducted on the first floor (against the ground) of the building and also underneath the first floor if there are spaces where people work or the social facilities are located there.
• If the workplace must make radon measurement because it has spaces located wholly or partly underground, the measurements must be conducted at least in the underground spaces.
• If the workplace is in a space that is equivalent to a dwelling, the radon measurement is conducted with two measurement detectors.
• For example, a warehouse with infrequent visits and very low occupancy (less than 20 hours per year can be considered short occupancy) will not normally need to be measured for radon if radon measurements have otherwise been carried out extensively in the premises. In such a case, it is unlikely that the radon concentration in the warehouse would be such that the radon exposure to a worker would exceed the exposure reference value of 500 000 Bq h/m³/year in all the workplaces used by the worker.
• In some special cases, a radon measurement must be carried out even if the working time in the workspace is very short. Such special cases include water treatment plants, poorly ventilated or earth-based spaces, and underground technical facilities, pumping stations and power transformers (e.g. in metro or other underground tunnels). In such spaces, radon levels can be very high, with even a short stay at these levels causing significant radon exposure.

If the radon measurement at workplace has been conducted using detectors from STUK’s radon measurement service, the radon measurement service sends a test report to the customer. The STUK's radon measurement service delivers the measurement results directly to STUK’s Natural Radiation Regulation.

If the radon measurement has been ordered from a private radon measurement company, the employer must notify STUK immediately of the radon measurement results (Radiation Act 859/2018, §146 and §155). The notifications are made via STUK's electronic service (STUK eGovernance). The measurements ordered from STUK don't have to be notified.

The notification is submitted via the electronic service and the measurement results must be attached to the notification.  Please make sure that you have the radon test report file (in electronic form) from the measuring laboratory available before logging in. The results will not be saved if the test report is missing.

All results are saved in the national radon database. Be prepared to answer a supplementary information questionnaire if your measurements show radon concentrations above 333 Bq/m³ (annual average above 300 Bq/m³). Additional information is requested on the surface area and number of employees in the workplace, the floor area of the measurement point, the ventilation, the number of employees and the annual working time at the measurement point.

If the e-service is not available, the results of radon measurements can be reported by e-mail to radonvalvonta(at)stuk.fi. Please also remember to attach the test report of the radon measurements to the notification.

Reference levels for radon

The radon concentration during working hours for regular work (over 600 hours per year) must not exceed 300 becquerels per cubic meter (Bq/m³). The radon concentration is calculated as the annual average of the radon concentration during working hours (measurement result x 0.9). The reference level of occupational exposure for radon is 500,000 becquerel hours per cubic meter per year. Exposure is calculated as the sum of the exposures accumulated during the year in all workspaces.

What to do if the measured radon concentration is higher than the reference level?

If the radon concentration measured for at least two months exceeds the reference level, the employer must conduct additional analyses or perform measures that reduce the radon concentration. STUK's inspector will contact the employer and ask for additional information. After this, STUK will give demands to the employer for further measures to be taken and deadlines to carry them out.

A few examples are below:

• The employer fills in a radon exposure calculator and if the radon exposure of workers is below the reference level of 500 000 Bq h/m³ on an annual basis (exposure is calculated as the sum of exposures accumulated in all workplaces during the year) - OK.
• The radon exposure calculator (in Finnish)
• If the ventilation of the property is not set with timing, the only option is to carry out remedial work on the property, i.e. radon mitigation. The planning of workplace radon mitigation is subject to the same rules as radon mitigation for dwellings. The success of the mitigation must be verified by an alpha track detector measurement lasting at least two months.
• Radon mitigation on STUK web pages (the link will be added soon)
• In properties where ventilation is set with timing, the radon concentration may be considerably lower during working hours than at other times. If the radon concentration measured with an alpha track detector in such property is bigger that the reference level, a so-called continuous radon measurement may be conducted, lasting for a minimum of one week.

Radon concentration during working hours

• Radon concentration during working hours on STUK web pages 
• To calculate the radon concentration during working hours, both a radon measurement with an alpha track detector and a continuous measurement are required, taken under the same conditions (no remedial actions between these measurements).
• If the radon concentration during working hours is above the reference level, radon mitigation must be carried out. The success of the mitigation must be verified by an alpha track detector measurement lasting for at least two months.
• Repair companies may carry out a continuous radon measurement after the repairs, which gives a quick result of the impact of the mitigation measures. This measurement alone is not sufficient to determine the success of the remedial measures, but a further alpha track detector measurement of at least two months is required.

If measures to reduce the radon exposure are to be taken at the workplace, these measures must be taken without delay. The adequacy of the measures must be demonstrated by similar measurements or calculations which have earlier shown the radon concentrations or exposure above the reference level. The results of the measurements must be reported to STUK.

The average radon concentration in a property can change for a number of reasons. STUK therefore recommends that indoor radon measurements should be repeated in workplaces, apartments and other living spaces

• every ten years if the previous radon concentration was higher than 100 Bq/m³;
• every ten years, if the reduction of the radon concentration below the reference level has been achieved by radon remediation;
• every five years if a radon remediation has resulted in a radon concentration below the reference level and the radon concentration before remediation was higher than 1000 Bq/m³;
• as soon as possible after any substantial structural or ventilation work (e.g. replacement of concrete slab, drainage or ventilation).
• Pressure ratios in a building can also change after, for example, window replacement: if there was a significant amount of replacement air coming in through the old window openings, new, tight windows can increase the negative pressure in the room, reduce ventilation and significantly increase radon levels.

The measurement of occupational radon levels is repeated when substantial changes are made to the ventilation controls that may have a significant impact on pressure ratios and hence on occupational radon levels. The measurement is always carried out first with an integrating measurement (an alpha track detector) of at least two, preferably three months.

If an annual average radon concentration of 300-400 Bq/m³ was measured at the time of the old Radiation Act, a new measurement must be taken within 10 years of the entry into force of the new Act, i.e. by the end of 2028, or earlier if the property undergoes major renovation work (Radiation Act 859/2018, § 202).