Radon gas dose rate calculator
Published: Jun 27, 2025
Source: Ionactive Radiation Protection Resources. Calculator programming by Chris Robbins of Grallator, article resource by Ionactive
Prelim
Ionactive presents a new resource section on radon gas related articles, and we kick off with a radon dose rate calculator.
Occupational exposure to radon (a naturally occurring radioactive gas which can enter buildings), is a recognised ionising radiation hazard. In the UK the Ionising Radiations Regulations 2017 (IRR17) require that employers undertaken an initial radon risk assessment to determine if further action (including mitigation) is required. The employer may need to provide notification to HSE and seek advise from a Radiation Protection Adviser (RPA).
Radon measurements are usually conducted passively (though active monitors are available). The output is usually in Bq/m3, which can then be compared to action criteria (e.g. notification to HSE where radon concentrations in air exceed 300 Bq/m3). Activity per unit volume of room air is not such a helpful parameter when explaining radiation risk, and particularly if risk comparison is required. The radon dose rate calculator provides output in effective whole body dose (micro Sv/h or mSv/year) which can be used directly for risk comparison (examples are given).
Other Ionactive radon resource
Whilst exploring the radon calculator you may wish to read other radon related resources on this website. One example is: Radon gas in schools (and other workplaces). This blog article discusses a boarding school which was fined £50,000 after pupils (and staff) were overexposed to radon gas. The calculator featured below can be used to deconstructed the information released by HSE about this school - you may be quite surprised with the results.
Radon gas dose rate calculator
How to use the radon dose rate calculator
Here is a summary of how to use the calculator. The red sections are not meant to be altered (but you can do so if you know why you are doing - we advise leaving them as they are).
- Mod F - this value recognises that there will be a dose contribution from Rn-220 which has a short half life of 56 seconds, and a higher dose contribution per decay. Rn-220 is difficult to measure so this factor corrects the total dose based on measurements of Rn-222 alone.
- IEF - this value (indoor equilibrium factor) accounts for the equilibrium of Rn-222 with its short lived decay products, in indoor air. The 0.4 value is a commonly recognised value for assessing indoor radiation exposures from radon. It recognises that there is not a perfect equilibrium between Rn-222 and its decay products (and it is these, such as Po-218, which contribute to delivering dose to lung tissue).
- DF - the dose factor which has units of 𝑛𝑆𝑣 (𝐵𝑞 ℎ 𝑚-3)-1 [UNSCEAR 2006, Vol 2, Annex E].
The yellow sections are the primary inputs which are as follows:
- Radon concentration (Bq/m3) - this is an input figure, usually obtained from passive radon monitoring reports, or perhaps from active radon monitor.
- Exposure time (hours) - this is usually the total time of estimated exposure in a year (which means the dose output is in mSv/y as noted below). If you are not sure of the exposure time just set it to one hour. Further examples of use are given later below.
The green sections are the primary outputs which are as follows:
- Total dose - the total accumulated exposure over one year in mSv (effective dose). Note this directly relates to the exposure time set in the yellow section, and the calculated dose rate.
- Dose rate - the dose rate in micro Sv/h.
Note: The total dose and dose rate are in terms of effective whole body dose. Radon gas delivers an equivalent dose to the lungs, the calculator converts this to a whole body dose (i.e. radiation risk), which can be used for comparison with more tangible radiation exposures (usually those you can easily measure directly with a conventional dose rate monitor).
Back calculation - You may wish to calculate the radon concentration (or total time of exposure) which would yield a maximum permissible dose or dose dose rate. To do this, proceed as follows:
- With the back calculation button set to Bq/m3, the concentration will be displayed for a given annual dose (enter in mSv/y).
- With the back calculation button set to hours, the exposure hours which would yield a given dose (mSv/y), for a particular radon concentration (Bq/m3), are displayed.
- If a dose rate in micro Sv/h is entered, the position of the back calculation button is irrelevant, and the radon concentration in Bq/m3 will be displayed (which would yield this dose rate).
Alternative red settings
Despite advising that the above red calculator values should not be changed, it is worth mentioning that they are based on UNSCEAR 2006 coefficients and methodology. An alternative approach is to use data from ICRP 126 which is given below. Within the margin of error (of radon measurements) these changes for 'normal' indoor exposure make little material difference (about a 47% higher), although this difference would become more of an issue over long exposure durations. The second set of values is for indoor work involving 'substantial physical activity' and radon exposures in tourist caves (!).
General work indoors
- ModF (ICRP) = 1.0
- IEF (ICRP) = 0.4
- DF (ICRP) = 17.25
Work indoors (substantial physical activity) & tourist caves
- ModF (ICRP) = 1.0
- IEF (ICRP) = 0.4
- DF (ICRP) = 35
Unless you know better leave the calculator in standard settings, and seek the advice of a Radiation Protection Adviser and / or a radon gas specialist.
A quick word from Ionactive
With every new (and existing) Ionactive Radiation Protection Adviser (RPA) contract, we now offer a real time radon monitoring service. We use real time active radon monitoring (conducted over a few hours during the client visit), combined with other information such as:
- Consulting the UK radon map
- Review of building / room layout
- Existence of basements and other below ground areas
- Occupancy in the workplace
This is used to produce an initial radon risk assessment. We do this regardless of the primary radiation source (e.g. x-ray systems, industrial radioactive sources, medical equipment etc). There is an expectation by the UK regulator (HSE - Health and Safety Executive), that holders of registrations or consents will consider occupational radon exposure in the workplace. [All workplaces should consider radon gas, but users of other ionising radiation sources are expected to know better].
Passive radon dosimetry placed into the workplace over a three month period is the standard method for on-going radon monitoring in the UK. However, for initial assessments (particularly when asking "Do we have a radon problem", or "Do we need to notify HSE"), real time radon monitoring with professional monitoring equipment is a sensible choice.
Do not rely on consumer grade active radon monitors purchased for £100 - £200 online. They are not that reliable - if in doubt ask this question: "Can I see the calibration certificate, issued specifically in compliance with IRR17" - if this certificate is not offered, the radon results are not worth considering.
Where professional equipment is available, the radon dose calculator can be used to provide dose or dose rate date from Bq/m3, to provide radiation risk comparators. Even if the results indicate that nothing more needs to be done (i.e. radon concentrations are < 300 Bq/m3), the calculator can still be used to show how low the actual radon risks are (e.g. by comparing to hours of flight during airline travel).
Using the radon dose rate calculator - examples
The examples below use the radon dose rate calculator with its standard red settings.
Example 1
Some initial radon monitoring has been conducted in areas around your workplace. All results are < 300 Bq/m3, except for an electrical cupboard (360 Bq/m3) which is accessed twice a year (total access time is assumed to not exceed 1 hour / year). You seek advice from a RPA, and notify the HSE. What is the radiological risk to employees or contractors who access the cupboard?
Using the calculator you note that the dose rate is 1.68 micro Sv/h (which means the total dose for an hour access per year is no greater than 1.7 micro Sv - whole body effective dose).
Consider a flight above the UK at 38,000 feet. The effective whole body dose rate to the flight crew and passengers (from cosmic radiation) is about 5 micro Sv/h. Therefore, entering the electrical cupboard for up to 1 hour per year is broadly equivalent to just over 20 minutes of flight. Using the calculator you have turned Bq/m3 into something much more understandable (revealing trivial radiation risk).
If you want this in another comparative form, then this is broadly equivalent to eating 17 bananas over the year (about 1/3 of a banana a week). [This comparison, sometimes known as BED or banana equivalent dose is based on the naturally occurring radioactive K-40 found in banana and many other foods. If you want to consider this further see: A banana smoothie or a glass of tritiated wastewater from Fukushima Daiichi nuclear plant? (Ionactive blog article).
Example 2
You are a document archive repository company. You have a building based on several floors which also includes a basement. Radon monitoring has taken place and whilst the ground floor (and upper floors) are < 300 Bq/m3, the basement area has recorded up to 4600 Bq/m3 in several places. Looking at access records, one employee has spent up to 100 hours in the basement archiving documents in the previous calendar year.
The radon concentration is significantly above 300 Bq/m3 and a notification to HSE needs to be made. The company also needs to seek advice from a Radiation Protection Adviser, and appoint them in writing. Using the radon dose calculator we see that:
- The dose rate is up to nearly 22 micro Sv/h.
- An accumulated dose of 2.15 mSv/y is possible (for 100 hours of exposure).
The whole body effective dose is way above a dose limit of 1 mSv/year (for other persons). The dose rate exceeds 7.5 micro Sv/h (averaged however you wish), and so this workplace would be a controlled area under IRR17. It is likely that this area will need radon mitigation to meet the ALARP principle (at least). Other control measures could include:
- Passive controlled area signage on the door.
- Local rules to control access.
- A limit on working time in the area
- Radon mitigation measures (as an engineered measure, this will often be at the top of this list)
- Employee awareness
[Ionactive comment: The above control measures are typical examples, nothing here is to be treated as formal RPA advice.]
Another obvious option is to see if the archive materials can be moved and the basement work terminated (note that this intervention - moving items - will have dose uptake implications).
Unlike our first example, the example 2 dose assessment results are not trivial. Whilst 2 mSv/year whole body dose is 1/10 of the legal whole body dose limit for employees, it is still substantial when compared to most UK employees working with ionising radiation (most are <1 mSv/year from occupational exposure and this includes nuclear industry workers).
It should be noted that 2 mSv/year is less than would be received by cabin crew working on long-haul airline flights over a typical working year. This does not justify the radon exposure (cabinet crew have no choice, whereas the archive repository company does have a choice where their employees work), but as a risk comparator, it could be used to help reassure.
Finally - we can use the radon dose calculator to determine a 'what if'. Such as 'what if exposure duration leads to > 6mSv/year, the point where a UK employee would need to be classified'. You can use the calculator - set the back calculate button to time, and enter 6 mSv/y into the green dose box. The results show that 6 mSv (whole body dose) would be exceeded after 279 hours of exposure (that is just under 6 hour / week based on a 48 week working year). This is about 1 hour 12 minutes a day - something entirely possible for the workplace scenario given.
The analysis clearly shows that substantial radiation exposures in the workplace are possible where employees work in high concentration radon environments.