Radon gas in schools (and other workplaces)

Boarding school fined £50,000 after pupils overexposed to radon radioactive gas

We recently become aware of news articles and an HSE press release regarding the over exposure of pupils (and teachers) at a private school (news released 20 July 2023). Some relevant links are as follows:

HSE press release: Boarding school fined £50,000 after pupils overexposed to radon radioactive gas (opens in a new tab).

BBC news article: Bath school given £50K fine for exposing pupils to radioactive gas (opens in a new tab).

Both the above links say more or less the same thing (i.e. BBC uses the HSE press release as the basis for their news article). Other media sources released similar articles based on the same HSE information.

A summary of the overexposures are as follows (the data is taken from the HSE press release and Ionactive will discuss this data later below).

At the private school the following radon exposures took place.

  • Five pupils were exposed to radon gas at levels that were 8 times the legal limit (they were living and studying at the school).
  • Two other children, who were not pupils (but living at the school with their parents) were exposed to radon gas at levels that were nearly 14 times the legal limit.
  • Two employees at the school were exposed to radon gas at levels that were 3/4 of the legal limit (they were living at the school and their children feature above).

The HSE press release states that the exposures took place in 2019. It is reported that the school knew there was a radon issue (as far back as 2007), but nothing much had been done since then, for the period 2010-2018.

Ionactive comment: It is accepted that HSE (and news providers) will often simplify information. However, there are no specific 'legal limit' for exposure to radon gas. Rather, the exposure to radon gas expressed in Bq/m3 (radioactivity per cubic meter of air) has to be converted to an effective dose in mSv (or micro Sv). It is the values calculated in Sieverts (Sv) which are then compared with dose limits contained in the Ionising Radiations Regulations 2017 (IRR17). Feel free to visit Ionactive guidance on IRR17 as required: Ionactive guide to Ionising Radiations Regulations 2017 (IRR17).

The Ionactive radiation protection glossary maybe useful some of the terms used in this article such as the Becquerel (Bq), radioactivity, radon, effective dose, sievert, alpha particles, etc.

If you do a (UK) search for radon on the internet you may see values such as 200 Bq/m3 (action level in a domestic dwelling), 100 Bq/m3 target level (for domestic dwellings, particularly for smokers or ex-smokers), and 300 Bq/m3 (from IRR17 for occupational exposure to radon in workplace, being the point at which an employer would need to notify HSE, monitor radon, undertake a radiation risk assessment, implement mitigation measures and simlar). Note in particular that the value 300 Bq/m3 is averaged over the whole year - so if radon measurements are made over a three month period (most common arrangement), or in real time using active detectors (less common), then this has to be seasonally adjusted to provide an estimated annual average (the laboratory analysing radon detectors will make these adjustments).

It is important to state the above values, since the prosecution is based on exposure in a workplace and therefore occupational exposure (not exposure in a domestic environment). Two parents and children are living at the school (i.e have a home on site), but it appears that this is treated as occupational exposure since the parents were living at the school by virtue of their work. Ionactive is using some speculation here, and this does not change the numerical values of exposure, but may have some bearing on "dose limits" and, as you will see later below, the exposures appear to fall between occupational exposure (of the parents / employees) and exposure to 'other persons' who are neither employees or trainees (i.e. they are pupils). So the pupils in this case are not employees, nor are they occupationally exposed, but they are affected by the environment of those who 'work in a radon atmosphere' (since they may be sharing the same space). Phew (!) - you may need to read over this paragraph a couple of times (we did).

We hope the above analysis is not too heavy going for any casual reader, but it is important when considering the multiples of dose limits indicated in the HSE press release.

It is also important to state at this point that the phrase '3/4 of a dose limit' does not indicate an exposure which is justified or acceptable. Whilst IRR17 provides dose limits, it also contains the requirement that exposures are as low as reasonably practicable (ALARP). When considering IRR17 is not good enough to simply be within (less than) dose limits, the employer has to demonstrate that the exposures are ALARP (which appears not to be the case when reading the HSE press release).

Radon Gas

There is much internet resource on radon gas and Google is your friend. The UKHSA resource 'Everything you need to know about radon' is a good start (opens in a new tab). 'Radon' (wikipedia) is good resource with much detail (opens in a new tab). 'Radon - WHO' (World Health Organisation) is also full of lots of useful and easily readable information (opens in a new tab). Feel free to read this resource and then return to this point.

Radon is a naturally occurring radioactive gas. It is derived from the rock geology below ground and is commonly attributed to granite rock formations (although see later in this article - a knowledge of geology is not a good indicator of radon risk). Radon is an alpha emitter and can be breathed in (and out). Generally the decay products of radon (e.g. Po-218, also an alpha emitter) are the greater issue since they are solid, and so could be retained in the lungs. However, measurement of radon gas (Rn-222) is a reliable indicator of overall radiation exposure risk.

Radon gas may enter a premises through its foundations (which is why below ground areas are always of potential concern). It can also enter through gaps in pipe runs and even via the water supply. Atmospheric conditions (low / high pressure) can sometimes have the affect of drawing ("sucking") radon out of the ground and into buildings (this partly relates to the seasonal affect mentioned earlier).

Since radon is a gas (quite a heavy gas too), it can be suppressed / moved by forced ventilation systems (both positive and negative pressure depending on circumstances). Therefore, some ventilation systems might actively encourage radon ingress into a building, whereas a correctly installed radon mitigation system will suppress ingress into a building and / or remove the radon and vent it outside the building. Impermeable membranes can also be used to supress radon ingress (these are best used during new builds since they can be installed into the foundations before the rest of the structure is erected). Where radon affected areas exist local planning regulations may require radon mitigation measures to be installed as a condition of planning regulations (this may also be a requirement of building regulations).

With respect to health effects, radon gas and its decay products will exposure the respiratory tract (lungs) to ionising radiation (i.e. alpha and beta particles irradiation). The interaction with lung cells, and particularly their DNA, can cause damage. The damage may lead to cell death, but more commonly may lead to cell damage - this is turn may create a precursor to lung cancer later on in life. It is important to note that there are many hazards in the environment that might lead to an increased risk of lung cancer, perhaps the most well known being smoking cigarettes. Other hazards might include chemicals at work, industrial pollution in the environment, asbestos and similar. So radon gas is only one of a number of factors which might increase the risk of cancer. It therefore makes perfect sense to do what we can to control radon induced cancer risk, since the measures are often quite simple (but not free of charge either) and they are local (i.e. control measures within the building you occupy). The subject matter of this Ionactive article relates to occupational exposure to radon in schools and workplaces, so there is an added incentive since there is a legal requirement to manage radon risks via IRR17.

Radon exposure - analysis of the HSE press release

What follows is our interpretation of the information contained in the HSE press release referenced (and linked) earlier in this article. We may not have this totally correct, but this is not a significant issue since the discussion here will be generally useful to all who are looking at radon exposure in schools and other workplace locations.

Dose limits

Teachers or other employees (e.g a caretaker) who are exposed to radon in the workplace are occupationally exposed. In the extreme, (since ALARP must be applied), the dose limit for such persons will be 20 mSv/year whole body effective dose. See Ionactive resource 'IRR17 (12) - Dose limitation'.

Pupils are not occupationally exposed (they are not employed to do work), but they could be exposed to ionising radiation in a workplace where occupational exposure to radon gas is taking place. Therefore they are 'other persons' and the dose limit would be 1mSv/ year whole body effective dose.

Teacher (employee) exposure

The HSE statement states that two employees were exposed to radioactive gas 3/4 of the legal limit. With a dose limit of 20 mSv/year, this implies that the exposures were in the order of 15mSv/year (for 2019). By any standards of occupational exposure (including non radon exposures in the nuclear industry, medicine, research, industry, aviation) this is significant. Average occupational exposure from all sources of ionising radiation across all sectors is unlikely to exceed 1mSv/year whole body effective dose (for the UK).

Pupil exposure

The HSE statement states that five pupils were exposed to radioactive radon gas 8 times the legal limit. With a dose limit of 1 mSv/year (for other persons), this implies that the exposures were in the order of 8mSv/year (for 2019). This is a significant breach of IRR17, and more generally the Health and Safety at Work etc. Act 1974 (link in new tab).

Do these exposure levels make sense?

As noted earlier in this article, the above values for employees and pupils have not been explicitly stated by HSE. However, reading the HSE statement shows a degree of reliability in our assumptions. In order to ensure our reasoning is clear, we will present the entire HSE press release paragraph we are analysing, the specific information we are considering is given in bold.

"...Five pupils at Kingswood School in Bath, Somerset were exposed to levels of radioactive radon gas almost 8 times the legal limit. Two other children, who were not pupils at the school, were exposed to levels of radon gas almost 14 times the legal limit. Two employees were exposed to radioactive radon gas ¾ of the legal limit. Exposures to radiation need to be kept as low as reasonably practicable..."

Here we see that two children (not pupils, and not occupationally exposed) had radon gas exposures of almost 14 times the legal limit, which would be around 14mSv/year whole body effective dose (14 x 1 mSv/year). We also see that two employees (we believe their parents) were exposed to radon gas at 3/4 of the legal limit, which for occupationally exposed persons would be 15 mSv/year whole body effective dose (3/4 x 20mSv/year). Given rounding (etc), it appears that the two employees and the children more or less received the same radiation exposure from radon (the only difference being the different dose limits applied).

As already stated, by occupational standards 15 mSv / year whole body effective dose is significant and right up there with the highest likely exposures to all UK workers in a given year (for all sources of ionising radiation use). That said, it is quite possible that persons NOT occupationally exposed (i.e. just living at home in high radon areas) could be exposed to much higher radon exposures (and these do NOT come under IRR17).

[At the end of this article we will briefly consider the case of home working / hybrid working where an employer permits an employee to work at home - something that has massively increase since Covid-19. It is not an exaggeration to state that a whole cans of worms could be opened. If you are working at home, in a radon atmosphere which exceeds 300 Bq/m3, you are occupationally exposed and your employer needs to do something about this - more than likely asking you to return to your official place of work].

What were the radon exposure levels at the school?

We cannot know this for sure from the HSE / media statements alone. However, the HSE / investigators would know since this is the way they would have assessed the exposures against IRR17 which lead to the prosecution. They would have either taken their own measurements, or used historical school data (or both). They may have also used real time active monitoring (such devices are getting better all the time where real time generally means averaged over an hour or over 7 days).

Whilst there is significant speculation in this section, assuming the exposure levels compared to dose limits are reasonable (as derived above), we can provide some representative values of radon exposure in Bq/m3.

Conversion of Bq/m3 radon to Sv

Disclaimer. The data which follows MUST NOT be used in any official UK radon risk assessment or similar. There are many variables to be considered (indoor equilibrium factor, Rn-222 dose coefficient, working level months, dose contribution from Rn-220, etc). Workplace radon exposure assessments should be calculated on a case by case basis and you should consider seeking advice from a Radiation Protection Adviser (RPA). For this article we provide a working conversion as follows:

300 Bq/m3 (radon) for 2040 hours / year = 2.9 mSv/year whole body effective dose

[Ionactive comment - for the curious! Some readers may have seen values reported as 300 Bq/m3 giving 2.2 mSv/year over a working year. This is based on 170 hours per month, or 2040 hours per year. However, this can be further modified by considering the contribution from Rn-220 (this has a much shorter half-life than Rn-222 and is derived from the thorium decay series, whereas Rn-222 is derived from the uranium decay series). To cut a long story short, the Rn-220 contribution (which cannot be practically measured in the workplace), leads to about a 30% increase in dose/Bq when measuring Rn-222 alone. Therefore, if you take 2.2 mSv and multiply by 130% you will end up with 2.9 mSv (rounded)].

With this in mind we can look at some of the HSE data and make some educated guesses / statements.

For example, to receive 15mSv/year (teacher / employee exposure), would imply a radon concentration of 1571 Bq/m3 (if the exposure was over 2040 hours). This would imply a constant radon dose rate over the period of 7.35 micro Sv/h.

Lower exposure duration would imply higher radon concentrations such as 3142Bq/m3 (for 1020 hours / year) or 6284 Bq/m3 (for 510 hours / year), which would imply a radon dose rate in the area of highest exposure reaching nearly 30 micro Sv/h.

[Ionactive comment. The dose rates noted above can be used for planning and dose assessment in the work place - their use in this article is to highlight the significance of the radon exposures noted by HSE. To avoid doubt, you cannot walk into the work area with a conventional dose rate monitor (e.g. GM based detector) and read off these values. Exposure to radon gas itself is not really the issue - if you breath it in, you will breath it out again. The dose and dose values reported in this blog article are derived from the dose delivered to the respiratory tract by radon progeny - these are short half life radioactive products from the decay of radon and are solid in nature, these may become lodged in the lungs etc where they deliver their radiation dose. Therefore when we have quoted whole body effective dose earlier, and where we discuss exposures such as 15 mSv/year or dose rates such as 30 micro Sv/h, these values are derived from exposures to the respiratory tract. They are converted to whole body effective dose so they can be compared with IRR17 dose limits (from which overall radiation exposure health risk can be derived if required). Another advantage is that you can then compare true whole body exposures - such as sitting in an aircraft at 35,000 feet being exposed to cosmic radiation, with radon exposure. Such comparisons are often useful when trying to explain radiation risk without needing to discuss the 'C' word (radiation induced excess fatal cancer)].

However you look at this, to receive 15mSv/year whole body effective dose from radon requires a radon concentration >>300 Bq/m3. Note that these calculated values take no credit from any radon mitigation system that might be installed.

The same analysis can be used to consider pupil exposures. Notwithstanding the children exposure (which was similar to the parent exposure as noted above), the HSE press release indicates (after Ionactive analysis) that pupil exposures were up to 8mSv / year (assuming dose limits for other persons is taken as 1mSv/year). A Google search shows that secondary pupils might spend 1462 hours / year at school (no reliable data could be found for a private schools). So 1462 hours will suffice. Assuming a radon exposure of 1571 Bq/m3 (see above), an exposure over a school year might lead to a whole body effective dose of 10.75 mSv/year. The HSE statement states 'Five pupils were exposed to radon gas at levels that were 8 times the legal limit', which we have said could be 8 mSv/year whole body effective dose. Given the unknowns (actual radon concentration, actual exposure time over a year, most radon affected rooms, lessons taken outside such as sports etc), then the 8mSv / year (or indeed 10.74 mSv/year) are within the expected order of magnitude (they make sense).

In all likelihood, radon concentrations would be far more distributed in terms of magnitude and location. Therefore to reconstruct an annual radon exposure (in mSv/year) would probably need data from a number of locations, estimated occupancy in those locations, adjusted for time of the year, ventilation (e.g open windows in the summer) etc. However you choose to look at this section of our article, and even if our assumptions or estimates are wildly out, it can be clearly stated that the exposures to radon gas were excessive, were not ALARP and breached health and safety legislation. Moreover, such exposures are considerably more than occupational exposures received working with ionising radiation in industry, aviation, research, medicine etc.

Do you have a radon problem in your workplace?

We could start this section by asking another question. Do you have a radon problem in your home? It is beyond the scope of this article to explore this in detail, but the answer is certainly, you could have. That said, we can use publicly available data, which is broadly based on measurements in domestic dwellings, to look at potential radon exposure in workplaces. (Other more detailed and accurate data is also available for a fee).

The free data is available at UK maps of radon run by UKHSA (this opens in a new tab). There is lots of useful information on radon on this website.

Let us first consider the school mentioned in the HSE press release - Kingswood School in Bath. This has the following postcode - BA1 5RG. We can enter that post code into the map search function at the above link (have a go if you wish!). What you will find is something like that shown in the picture below.

Radon Blog Radon Data 1

Radon Map for BA1 5RG with maximum magnification (1 km blocks)

In the above graphic the following information can be noted.

  1. The blue / white arrow shows the location of the postcode and position of the school.
  2. The colouring can be read against the legend which shows that the maximum radon potential is 10-30%. The UKHSA defines radon affected areas as those with a 1% chance or more of a house having a radon concentration at or above the Action Level of 200 Bq / m3. The postcode we have looked at has a probability which is significantly > 1% (so it is certainly a radon affected area).

It should be noted that the criteria relates to the 200 Bq/m3 action level (domestic dwelling), this alone does not mean there is certainty that a property is above the 300 Bq/m3 (the level which if exceeded in IRR17 would require action to be taken in workplaces). However, there is a good chance that radon concentrations, when averaged over a year, could be > 300 Bq/m3 and this alone means the employer needs to obtain RPA advice, undertake a radiation risk assessment which will likely include radon monitoring.

Further action will not be required where < 1% (0-1%) is specified on the map, except in below ground areas, where persons work for more than 1 hour / week averaged over a working year, in this case an assessment is required regardless of what the radon map says (i.e. even in areas denoted < 1%).

So in summary, Radon risk assessments should be carried out in

  • all below ground workplaces in the UK; and in
  • all workplaces located in radon affected areas (i.e. > 1% as shown by the map).

Below ground workplaces would include basements, cellars, mines and tunnels etc.

Ionactive comment: We will now zoom out the map and look at the school in context with the surrounding area (please do the same if you are following us). It becomes obvious that there is a huge potential for many other workplaces, including schools, which could be subject to radon exposures with concentrations above 300 Bq/m3 (averaged over the year), and so come under the requirements of the IRR17. Employer beware - if radon concentrations exceed 300 Bq/m3 at your workplace you need to make a formal notification to HSE under IRR17 (this is a legal requirement). Therefore HSE has a database of known workplaces which have radon issues, where action has been taken and where it is possible that radon mitigation equipment (radon pumps etc) are in place (and therefore need maintaining etc). However, more importantly, HSE will know of workplaces which may be in radon affected areas which are not on their radon notification database. It is possible that HSE (or local authority) could turn up at any workplace, which is not on their notification database, and ask about radon gas. Ignorance is no defence.

Radon Blog Radon Data 2

Radon Map for BA1 5RG zoomed out to show surrounding areas

Imagine the number of workplaces (schools, factories, office buildings, shops, restaurants etc) in the above graphic.

We can then zoom out further still as shown in the graphic below.

Radon Blog Radon Data 3

Radon map of the south / south west of the UK

In the above graphic we begin to see areas which are not radon affected (i.e. in the < 1% category). Workplaces in these areas do not need to consider radon as long as they have work areas which are above ground (or possibly below ground areas which are infrequently accessed). Below ground work areas need to be assessed regardless of radon affected status.

Ionactive comment: Whilst HSE radon information (Radon in the workplace) implies a test of occupancy in below round areas in non-radon affected areas (e.g. 1 hour per week averaged over a working year and / or places accessed for more than 50 hours / year), our advice is that any below ground area which is 'worked in' should be considered a radon exposure risk. A degree of proportionality is still required here - for example, it might not be proportional to undertake a radon risk assessment for a below ground switch gear room with is literally accessed once a year for a few minutes. The problem with this is that rooms can be repurposed over time and therefore occupancy can creep (upwards). Also note that if below ground work places are in radon affected areas, then an assessment is required regardless of occupancy level.

So to return to the question at the beginning of this section - Do you have a radon problem in your workplace? The answer is perhaps yes, quite possibly you do. This is not meant to scare or stress the casual reader (or school head teacher!) who happens to come across this Ionactive blog article. Doing nothing (unless you are really sure you need to do nothing) is not an option.

It's all about the geology (well kind of ..)

It is generally accepted that you will have potential radon exposure in buildings where the underlying bedrock is granite (since granite contains uranium and Rn-222 is part of the uranium decay series). So first consider the SW of Cornwall, an area known for potential radon exposure with granite underlying.

Consider first the radon map of this area - looking at St Just in the West to Truro in the East . Note that the radon potential across the whole region ranges from 10-30% to greater than 30%.

Radon Blog Radon Data 4

Radon data for SW Cornwall

Now consider a geological map of the same area. The pink and reds are various granites, the green and light brown colours are various slates, and the darker brown colours near Truro are sandstone and argillaceous rocks. One might expect that radon would be considerable in the West near St Just ("built" on granite) and less so in the East near Truro ("built" on sandstone). But this is not what appears on the radon diagram above.

Radon Blog Radon Data 5

Geological data in the region, showing granite (pink) to the West and sandstone (brown) to the East

So what could be going on here? Potentially a number of things (maybe some beyond Ionactive technical knowledge). However, it is useful to look at a cross section of the region and see the geological formations from that perspective - this is shown in the graphic below.

Radon Blog Radon Data 6

Geological section between St Just and Truro

Note that granite runs along the entire cross section, but only breaks the surface in certain places (e.g. St Just). Although Truro resides on sandstone it can be seen that there is granite below and to the sides and all it takes is for fractures to allow radon gas to percolate through and arrive in the basements and buildings above.

What about the geology under Kingswood School?

The graphic below presents geological data for the area underneath and around Kingswood School.

Radon Blog Radon Data 7

Local geology around Kingswood School

As you can see - Fuller's earth, limestone and sandstone are present. But there appears to be an absence of granite! This goes to show that local geology, at least near the surface does not necessarily have a bearing on the radon risk present. It might well be that deep down uranium bearing rocks are present and over time the uranium (or thorium) decay series has shifted such that parts of the decay chain are incorporated into other local rock formations. Or there may be fractures such that over time radon can percolate from deep down in the crust and arrive at surface level.

Whatever is the reason, this shows that it is not reliable to rely on geology alone, and this is why the UKHSA radon survey and data is so important - so please use it!

What next - what should I do now regarding radon exposure?

The HSE prosecution of a school shows that HSE means business. Hopefully this blog article has highlighted the fact that many workplaces in the UK could have completely missed the radon issue and could be liable to HSE enforcement action for exposing employees and other persons to radon gas and the resulting health effects.

Notwithstanding the risk of regulator action, in this specific case the exposures to employees, pupils and children were significant, way beyond average exposures to those who work with ionising radiation in the UK (all sources). Indeed, in a league table these exposures would likely be right near the top of all (known) occupational exposures (whole body effective dose) in the UK. The exposures to other persons (the pupils and children) is particularly troublesome - 8 times a dose limit is intolerable.

Certainly consider speaking to a Radiation Protection Adviser. There are a number of radon contractors who may offer a complete service - i.e. radon review, risk assessment, radon measurement and mitigation. If this blog article gains significant interest then we would be happy to feature them below. Ionactive is RPA to some of the biggest companies in the UK, who may be affected by radon gas exposure, so we are unlikely to able to support individual enquires from small companies and schools etc.

I work from home - does my employer need to consider my exposure to radon gas?

Yes they do. Since Covid-19, home working / hybrid working has expanded and therefore the employer will need to take an active interest in health and safety in the home office space. It naturally follows that the employer will also need to consider radon exposure. This is probably best described as a grey area (or can of worms!), since there is a crossover between domestic exposure to radon vs occupational exposure to radon gas.

If you work at home and are concerned about radon ('in the work place' - your workplace), then head over to the UKHSA radon maps as a starter. Depending on what you find and / or if you just fancy some advice, then consider talking to a Radiation Protection Adviser.

Mark Ramsay

Radiation Protection Adviser / Chartered Radiation Protection Professional

Ionactive Consulting Limited

(c) July 2023

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