Radon
- Radon is a colourless and odourless gas that is heavier than air and highly radioactive.
- In the klint zone of Northern Estonia, the radon concentration in the soil air (at a depth of 1m) exceeds the recommended limit value by up to 8 times
- Radon is a risk factor in all buildings, new and old, with and without a basement
Properties of radon
By radon, we mean the isotope Rn-222 of the radioactive noble gas radon that occurs naturally and which is the source of ionising radiation.
Indoor radon concentration is the radon activity concentration, i.e. the radon activity concentration in air per unit volume [Bq/m³].
The reference level for indoor radon is the annual average indoor radon concentration, above which it may be necessary to take appropriate measures to reduce the radon exposure of employees.
In an enclosed space, radon can accumulate to harmful levels, in the case of which long-term exposure (decades) can lead to lung cancer. No other health effects of radon have been established.
How does radon enter buildings?
Radon can enter a building along the following paths:
- cracks in the floor,
- structural joints,
- cracks in the walls,
- cracks around pipes (water, sewerage and other communications),
- gaps under the floor, gaps in the walls,
- tap water.
- Barometric pressure can also play a role in pushing ambient radon into the house.
Schematic: Proportion of radon sources in radon concentration.
Health effects
Radon enters the body mainly through the respiratory tract, but the highly radioactive daughter elements of radon can enter the body through food and water. As radon daughter elements attach to airborne dust and other particles, radon levels are higher in dusty and smoky rooms. In a confined space, radon levels can rise to levels that over long-term exposure (decades) may cause lung cancer. No other health effects have been detected on radon.
Reference levels for indoor radon concentrations
The reference level for indoor radon concentration in workrooms is 300 Bq/m³, unless otherwise specified in relevant legislation.
(For instance, subsection 9 (4) of the Regulation No. 131 of the Government of the Republic of 6 October 2011 “Health protection requirements for the land, buildings, premises, furnishings, indoor climate and maintenance of preschool child care institutions” states that the annual average indoor radon concentration should be less than 200 Bq/m³ and gamma radiation dose less than 0.5 µSv/h.)
Measurement
The measurement of indoor radon concentration in workrooms must be completed by the end of July 2023.
The measurement of the indoor radon concentration in working premises must be carried out within five years since the land area was added to the list of land areas with increased radon risk, i.e. in Tallinn until 06.08.2023. You can find the list here.
Although it may seem that there is still ample time, it is recommended to start the process of measuring early, as it requires at least a few months and there are only a few professionals in Estonia who are capable of measuring indoor radon concentrations.
The employer is responsible for organising the measurement of indoor radon concentration in a workroom that is in a high-risk radon area and located:
- underground;
- on the underground floor of a building;
- on the floor of a building, the exterior wall of which is in contact with the ground;
- or on the ground floor if there is no underground floor.
In the klint zone of Northern Estonia, the radon concentration in the soil air (at a depth of one metre) exceeds the recommended limit value by up to eight times. Areas with elevated radon concentrations also occur in Eastern and Southern Estonia. In Western Estonia and on the islands, the concentration of radon in the soil air usually does not exceed the limit value.
Indoor radon concentration is deemed compliant with the reference level if:
- the result of a one-year continuous measurement does not exceed the reference level;
- the result of a continuous measurement lasting for at least two months from 1 November to 30 April does not exceed the reference level by more than 20%.
If mechanical ventilation systems operating during working time are used at the workplace, the employer may additionally organise the continuous measurement of diurnal variation of radon concentration. The continuous measurement of radon concentration to determine the mean value during working time is carried out between 1 November and 30 April. Continuous measurement is carried out in addition to the one-year continuous measurement or the continuous measurement lasting for at least two months from 1 November to 30 April.
If the result of continuous measurement does not exceed the 300 Bq/m³ mean value of radon concentration during working time, indoor radon concentration is deemed compliant with the reference level.
Measurements must be repeated:
- every ten years if the indoor radon concentration is compliant with the reference level;
- every five years if the indoor radon concentration exceeds the reference level;
- if significant structural changes have been made in the workroom after radon measurement.
Measurement results of indoor radon concentrations must be traceable in accordance with the procedure provided by the Metrology Act.
The traceability of measurement results is proven if a verified measuring instrument is used for measurement, and:
- the measurements have been made by a competent measurer who has been accredited or recognised as a professionally competent measurer, following the relevant measurement methods;
or
- the measurements have been made in compliance with the detailed requirements for the measurement procedure and the processing of the measurement results deriving from the Metrology Act or another Act and legislation established on the basis thereof.
Measuring radon concentration in workrooms must be based on standards EVS-ISO 11665-4 and EVS-ISO 11665-8, if measuring the annual average concentration of radon, and standard EVS-ISO 11665-5, if measuring daily changes in radon concentration based on the continuous measurement method.
In short, one of the following requirements must be met – the measurements have been carried out by a competent measurer, following the relevant measurement methodology, or the measurements were based on the requirements of the aforementioned standards. Therefore, the contracting entity has to decide which to choose – whether to use the services of a competent measurer or verify later based on the relevant standard whether the measurements carried out meet the requirements.
Implementing measures to reduce health risks
If the measurement reveals that the radon concentration in a workroom exceeds the reference level, the employer takes structural improvement measures or limits the working time to reduce the health risks of employees where appropriate.
Since the planning and implementation of structural improvement measures require time, the employer will, upon becoming aware of the exceedance of the reference level, first limit the working time.
When limiting working time, the number of working hours authorised per year (T) is calculated according to the following formula:
T = 600,000 / RM, where RM is the measured indoor radon concentration [Bq/m³].
For example, the average radon activity concentration in the first room during the measurement period is 1,470 ± 330 Bq/m³ and in the second room 880 ± 200 Bq/m³.
To calculate the working time limit, we recommend using the higher value as the basis, since we are dealing with the need to protect human health and a higher value is also possible based on the results of the measurement. Thus, in the first room, the calculation process is as follows: 600,000 / 1,800 = 333. This means that an employee is allowed to stay in the rooms to which this calculation relates for 333 hours per year.
In the second room, the employee may stay for 555 hours per year. The calculation process is as follows: 600,000 / 1,080 = 555.
The employer can implement the working time limit from the moment they become aware of the exceedance of the reference level, i.e. the date of issue of the measurement report. Please note that a year is not a calendar year, but a 12-month period following, for example, the date on which the measurement results were obtained.
Structural improvement measures
If the employer does not want to implement the working time limit indefinitely, they have the obligation to take structural improvement measures. If the requirements of the Estonian standard EVS 840 have been followed in the implementation of structural improvement measures to prevent the release of radon from soil to indoor air or to improve indoor ventilation, it is presumed that the implementation of structural improvement measures complies with the requirements of the regulation. After the execution of improvement measures, a new measurement must be organised to ensure that the measures implemented reduced the radon concentration to at least the level required. The employer can waive the working time limit after the imposition of structural improvement measures and after verifying that all measures were effective (measurements).
Informing the Estonian Environmental Board
The employer is obliged to inform the Estonian Environmental Board of any workrooms where the result of the control measurement of indoor radon concentration continues to exceed the reference level even after the implementation of structural improvement measures, by forwarding to the Environmental Board the radon measurement reports and a list of structural improvement measures.
Monitoring the effective dose of employees and medical examination
The employer must measure the effective dose of employees once per year if the indoor radon concentration continues to exceed the reference level even after the implementation of structural improvement measures. An effective dose is the sum of the equivalent doses multiplied by tissue weighting factors which characterise differences in sensitivities to radiation of human tissues and organs. Equivalent dose is the absorbed dose in the human tissue or organ multiplied by radiation weighting factor of effective radiation. The unit for measuring the effective dose is sievert [Sv], usually millisievert [mSv].
The effective dose (E) of an employee per year in millisieverts is calculated according to the following formula:
E = 6.7 × 0.000001 × RM × t, where RM is the measured indoor radon concentration [Bq/m³] and t is the working time of the employee per year [h].
On average, there are 1,848 working hours per year (an average of 168 working hours per month multiplied by 11 months).
For example, the measured indoor radon concentration is 458 Bq/m3 after the implementation of structural improvement measures.
6.7 × 0.000001 × 458 × 1,848 = 5.67 mSv.
The employer organises the medical examination of an employee once a year if the effective dose of the employee exceeds 6 mSv per year. The medical examination is conducted by the occupational health doctor in accordance with the general procedure. The effective dose limit for employees is 20 mSv per year.
In this example, there is no need to organise a medical examination of the employee once a year because the effective dose of the employee does not exceed 6 mSv per year.
Informing the employees
Please note that, depending on the measurement results, the risk assessment of the working environment must be amended because there is new data on a working environment hazard (radon) and its effect on the health of an employee. After amending the risk assessment, it should also be introduced to employees, as they need to be aware of the results of the risk assessment of the working environment, the health risk associated with long-term exposure to radon, and the measures taken to prevent damage to health.
Employees must be aware of the measurement results of indoor radon concentration in their workroom, as well as health risks and the measures taken by the employer to prevent or reduce health risks. If it is necessary to limit working time, employees must be informed thereof, employees must also be aware of the effective dose if its calculation is required.
