In researching the subject of Radon mitigation, I came across this article, Titled "Radon - A brief discussion", by Caoimhín P. Connell (Forensic Industrial Hygienist)

Please read that whole article before posting any comments. It's a long read, but I'd like to ensure everyone who comments on this topic has in fact read and understands the article. No biases please! :)

The first paragraph states the following:


A large portion of the general population is under the misconception that the frequently published risks associated with radon are well accepted scientific facts. In reality, the vast majority of well designed studies do not support policy or positions that exposures to indoor radon pose a significant threat to health, and indeed, the majority of those studies indicate that, at concentrations typically seen in homes, as the level of radon increases, the risk of lung cancer goes down, not up.


After reading the science behind Caoimhín's well-written and thorough article, I have to say I agree with his words and message. So what does that mean to an energy auditor? What advice am I to give to a homeowner whose home is under constant depressurization causing backdrafting with their woodstove or failing to pass worst case combustion safety tests, all because of their radon fan in the (nearly-conditioned) crawlspace? I realize as a BPI graduate I am supposed to consider Radon. But what do I tell folks whose Radon mitigation system indicates levels far below 7 picocuries? Should they run that fan that consumes 526 kWh/year, costing them $70/year?

I welcome your input. Love this community!


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A correction to my last posting...

Said, "a two story 2k sq-ft home right next to a one story 2k sq-ft home would have double the radon problem"

Meant, "a two story 2k sq-ft home right next to a one story 2k sq-ft home would have half the radon problem"

Good morning, Gents –

Great questions and comments –

First of all, just for full disclosure, although I was one of the original group of people to get certified under the US EPA Radon Proficiency Program, I have never been involved in routine residential radon issues.  I will get involved as an expert witness when necessary, but I mostly deal with radiation issues in industrial, occupational and mining related scenarios.  So, for example, if hospitals, or mines or factories have radiation issues, I will get involved; if someone calls and asks us to do radon monitoring in their home – we send them to our web site, but otherwise don’t get involved.

I have no axe to grind with radon testers or Mitigators provided they don’t go out on a limb and pretend they know something about radiation toxicology when they don’t – as long as they just stick to the simple cookie-cutter discussions, I view them as responding to a fear-based response they didn’t create and are just filling a commercial need, however, baseless the need.  Much the same way that if an homeowner was under the false assumption that painting your house blue gives you brain cancer and so he hires a house painter to paint his house white – who would blame the house painter?

I have always equated square footage to the saturation of radon in a home. For example, a two story 2k sq-ft home right next to a one story 2k sq-ft home would have double the radon problem.

This would not be a correct assumption.  To start with, when someone speaks of radon measurements, they have not actually measured the radon – ever.  Therefore, we need to start by recognizing that there is not a single “radon testing” device on the market being used by radon industry that actually measures radon.  Therefore, if you took 1,000 houses, each with exactly 20 atoms of radon per liter of air in the house, and you hired 1,000 radon testers to do their usual testing, you would end up with Gaussian distribution of “results” that would range from less than 0.5 pCi/l to 15 pCi/l, even though all houses had exactly the same radon concentration.  This is because the unit “pCi/l” is not a unit of concentration and is not an expression of radon concentration.  The unit “pCi/l” is a unit of activity per unit volume and, say, 5 pCi/l could come from an house with 10 atoms of radon per liter of air, of from an house with 10,000 atoms of radon per liter of air. 

So, to answer your first question – let’s just deal with radon and not with “radon equivalents expressed as pCi/l.”  If you had two houses next to each other, each built on exactly the same geological foundation with the exactly the same soil communication properties, etc. -  except one was a two story 2k sq-ft home right next to a one story 2k sq-ft home, there would be no way to predict which would have the higher radon concentration (and certainly no way to predict which would have an higher “pCi/l” value. 

The concentration of any gas in an home is a compartmental evaluation – that is, the concentration will be different for each room, predicted by three parameters:

1) The total sources
2) The total sinks
3) The mixing factor

I put the model used for the prediction here:

As Seán points out, the main driving force for soil borne radon in an home is the “stack effect.”  And, all other things being equal, the “stack effect” in a 2- story house will be more pronounced than in a single story house, simply because the “stack” in a 2- story house is taller. 

Depending on the specific house, the radon level in the water could be the single greatest contributor, and in my experience, without exception, the houses that are truly elevated (500 pCi/L and up) have exclusively been due to radium in the water decaying to radon.

“Again, in most cases, won't a balanced ventilation system solve most of these issues?”

I don’t know how you are using the term “balanced ventilation.”  Every ventilation system is “balanced” to the extent that ultimately every liter of air that is removed from a structure is replaced with a liter of air, and the net pressure differential is zero.  Even structures that are maintained under positive pressure, or under negative pressure are still a net-zero system.  I just wrapped up the commissioning of two new emergency Operating Rooms, that ran at 0.05" WC yet air in=air out; and in the receiving hallway and lobby air in = air out even thought there was a pressure differential as one moved from the Operating Room into the surrounding areas.  Having said that, the ventilation in virtually every home in North American is such that the radon is properly controlled without a “radon mitigation system.”  There are only a handful of houses in the entire US that have a legitimate radon problem – probably much fewer than 1,000 homes in the entire country. 

“Why is this not mainstream information?”

It is mainstream information – in the scientific world.  In the irrational world of the US homeowner who watches Channel 7 News the mainstream information that toxic black mold killed Ed McMahon’s Dog, and Saran Wrap is exuding dangerous phthalates and their microwave oven is causing brain cancer, and the overhead power lines are causing leukemia, and ….(fill in the fear du jur)…

There seems to be a significant disconnect between radon mitigation contractors and home performance contractors. Do the radon folks know?

Generally, no – Very, very few “radon contractors” whom I have met know anything about radon - when the EPA Radon Proficiency Program was developed, the certification was pitched at a 6th Grade Level on purpose.  If a Health Physicist, or a Radiation Safety Officer or Industrial Hygienist took the EPA RPP test, they would have failed the certification program – because they would have answer the test questions correctly.  To pass the certification test it was necessary for the participant to answer the questions “the EPA way.”

Do conditioned crawlspaces (thick polyethylene sheeting sandwiched under rigid foam attached to foundation walls) work to "push" the radon sideways and out the sides of a foundation? Or does radon travel through thick poly? I haven't been able to find any information about this.

As Seán points out, in the case of radon and homes, the air is always pulled and never pushed.  Radon, being an ideal gas, will always, always, always, travel from an area of high pressure to an area of low pressure – pressure differentials in the crawlspace will certainly be affected by vapor barriers, and other types of barriers.

I'm intrigued by this article by Martin Holladay.

There is no such thing as “exhaust only” ventilation.  Air in always equals air out.  If you exhaust air at one point, you introduce air in at another.  Having said that, a glance at Holladay’s article indicates he kind of missed the point.  If one had a MASSIVE exhaust fan in an home with a crawlspace, and the fan was pulling 20” WC static pressure, and makeup air was through cracks in the building shell then the “exhaust only” ventilation would have no impact on the radon concentration.  If you replaced that fan with one that was pulling 0.02” WC and that resulted in 0.02” WC pressure differential across the radon laden crawlspace, that fan would increase the radon concentration in the home (all other things being equal).  It rather like saying “Larger engines are less fuel efficient” intuitively neat, but technically false – (consider a diesel locomotive on a train). 

And they need to stop depressurizing people's homes, causing all sorts of other issues along the way.

There are no radon mitigation systems that I know of wherein one depressurizes an home – perhaps you are thinking of sub-slab depressurization systems or crawlspace depressurization systems.  In those systems, the delta-P across the building shell of the home is unaffected.

I hope this helps.


Milk = 1,200 pCi/l alpha
Wine = 300- 800 pCi/l alpha
Beer = 800 pCi/l alpha 

Let’s play the numbers game!

A reaction is to ask why gas spectrometry isn't used on air samples to actually measure the radon?

I'm learning SO MUCH from this discussion! Thanks everyone!

Is all Alpha radiation equal insofar as it's capacity to damage human tissue? 

Does the Alpha radiation of the banana and other household items to which you refer degrade into Polonium 218 and create the risk for double strand DNA damage in lung tissue? 

If not, then why do you keep putting it out into these discussions? 

Thank you. 

Hello Mr. Cullen –


You ask:

Is all Alpha radiation equal insofar as it's capacity to damage human tissue?





You ask:

Does the Alpha radiation of the banana and other household items to which you refer degrade into Polonium 218 and create the risk for double strand DNA damage in lung tissue?



Your question is predicated on a false premise.  Alpha radiation does not breakdown into anything (including polonium 218), and neither does it matter if it is from a banana, or granite or any other source, and therefore the nonexistent "break down" product would not be capable of anything at all.  


Your question is rather like asking  “Do bicycles from Russia break down into Cadillac Escalades which could then win the Daytona 500?”  Since bicycles never breakdown into cars of any kind, it doesn’t matter if the bicycle is from Russia or anywhere else.  And since bicycles never breakdown into any kind of car, one doesn’t have to specify which car it will not have broken down into and neither does one have to specify what that car may have done once the transformation is completed.


As such, alpha radiation, for all practical purposes, never breaks down into anything ever at all.  An alpha particle is essentially an helium nucleus that is stripped of its electrons.  That nucleus travels through a medium creating ionized pairs from which the alpha acquires its requisite stabilizing electrons and then become a stable helium atom from which there is no further “breaking down.”


I hope that helps.

Hello Tom!

I spent many, many years as an analytical chemist and for the life of me I can’t say I ever analyzed for radon in the lab.  However, I suspect that you are referencing a “mass spectrometer” instead of a “gas spectrometer.”  I have often measured helium using a  mass spectrometer whose magnetic deflector was specifically set to detect helium.  I use the system to study fugitive emissions of contaminants through structures.  In theory, one certainly could use a MS for the analysis of radon, but, I think it would be extremely difficult.

For a start, unlike the other noble gases (He, Ar, Kr, Ne and Xe), radon is not stable.  So, the amount you have collected at the site would not be present at the time of analysis and so ensuring a good record of time of collection and time of analysis would be imperative.   Second of all, the levels in homes is extremely low, and probably below the detection limit for the method.  Third is the costs would be very high and the radon industry would crash overnight!

Another problem would be the capture and collection method- other than physically collecting a large volume of air and actually shipping the air to the lab, I can’t think of a good collection method off-hand.  I assume there is some kind of a molecular sieve out there for that application, but I’m not aware of the medium.

Finally, measuring the radon is actually not particularly useful, since radon is 100% biologically inert.  That is, one could safely breath an atmosphere containing 80% radon as long as the balance was oxygen and a smattering of CO2 to control blood chemistry - (that would be a concentration of 16,600,000,000,000,000,000,000 radon atoms per liter of air!)

This is because the issue with radon is not actually the radon at all, but the “SLRDs” (short-lived radon daughters).  The radon concentrations are actually independent of the SLRD concentrations, (the radon concentrations merely identify an upper limit of SLRDs).  Therefore, one could easily have extremely elevated levels of radon in a mine for example, and have a low exposure to SLRDs, or one could have a lower concentration of radon in a mine, and yet have dangerously high levels of SLRDs.

Imagine two exactly identical homes right next to each other occupied by identical twins.  Both houses have radon concentrations of exactly 2,000 radon atoms per liter of air.  The twins do EXACTLY the same things at exactly the same times (open windows at the same time, cook at the same time, heat the house exactly the same way, etc.).  Except one twin likes to burn Yankee scented candles and one twin hates all candles.  If we measure the radon concentration in the two houses using mass spec, we will see the radon is exactly the same in both houses, but the SLRD concentration in the house with the candles is much, much lower than in the house without candles.

The exposures to radon are exactly the same for the two properties, but the cancer risk in the two properties is significantly different, and the cancer risk in the house that burns the candles is lower than the house where candles are not used; because the house with the candles has a significantly lower concentration of unattached SLRDs.


After posting I was recalling gas chromatography line absorption nothing fancy.

Is there a problem with measuring radon in a room? Measuring gases is quite usual in ecology & geophysics for CO2, CH4 and in volcanology a lot more gases with instruments so I had no idea identifying gas composition and proportions was so difficult for radon, it's some kind of special, eh?

Also noticing how radical mitigation is if you need it, consider that there can be a more worthy goal from all the work and money. I'll state that is a thermal upgrade to take space and water heating off the bill of by-the-Joule cost and use a solar-thermal system to gain the heat and electricity to move air & fluids with pumps & blowers.

The wet basements I've fixed use the same idea and where I'm coming from, bad groundwater mgmt, and to fix that and make a more cozy basement with soils that stay below 50F all year you need to insulate on the outside of the cement to use the wall as thermal-mass to the interior to get a cozy room.

If it's a crawl space, that's converted into a thermal-mass for storing heat-cold using solar thermal and  isolated from grade, one must still insulate the outside of the foundation down to the footing toe and grade level where a gravel drain takes away water, a blanket wall against insulation to allow drainage from the soils, this also vents air to outdoors.

This gives a heating-cooling bill of less than $100/year for most homes once capacities match the site.

Therefore this radon problem is all rather secondary if adding solar-thermal system yet the radon can be a legal or market-price reason to have to do something.

Seeing it's controversial and knowing the benefits of doing a solar-thermal upgrade my take is that for most people with a radon problem on the table it would be worth studying for their site, collectors don't have to be attached to the home.

Caoimhín, can you explain why burning a candle reduces short lived radon daughters (SLRD)? I'm not sure I understand that. Would a pilot light on a water heater or boiler or would a stovetop or woodstove burning also do the same?

Hello Rodney – Candles and radon:

It’s all about transport mechanisms. 

Radium is a radioactive material, and its salts are very soluble and readily dissolve in ground water (vadose zone water) and that vadose zone water flows around and directly under houses.  This is the transport mechanism that gets the radioactive materials of concern to the proximity of the house.

All of the radium daughters are solids, except one, radon, which is a gas, and unlike the radium from which it comes, radon has an extremely high Henry’s Constant, meaning it does not like being in water, and therefore, it immediately leaves water and enters any air space around that water.  This is the transport mechanism that gets the radioactive materials into the air.

When the radon decays, it produces the SLRDs (Po-218, Pb-214, Bi-214, Po-214), these are charged particles, and as charged particles, the SLRDs “want” to be attached to something to neutralize the charge.  If the SLRD comes into contact with a wall, a table, your dog, a ceiling fan blade, a pollen grain, dust mote or mould spore, it attaches to the surface of that object, and is said to “plate-out.”

An SLRD that has plated-out no longer has an high probability of travelling into the deepest portion of the lungs, the little air sacs known as the alveoli.  The transport mechanism of transport to the deep lungs has been interrupted.

The unattached faction, on the other hand, will be transported into the alveoli, where it will now become attached to the epithelial cells of the little air sacs, discharging it’s alpha pay-load directly into the cells in the lungs. 

The risk associated with the carcinogenesis  of radon hinges directly on the concentration of the unattached SLRDs.  The ratio of unattached SLRDs to radon is part of a parameter called the “equilibration ratio” (ER).  The ER in a perfectly still air system with no movement except Brownian motion and no particles in the air will have a value of approximately 0.999   If you start to move the air with a ceiling fan,  the unattached faction starts to plate out on surfaces, and is significantly reduced, and the ER can drop to 0.1  If you light a candle (especially a scented jar candle), the candle produces a prodigious quantity of “ultrafine particles”  (UFPs).  The UFPs “mop up” the unattached SLRDs thus removing the transport mechanism of the SLRDs to the deep lung. 

Any activity that reduces the concentration of unattached SLRDs, but leaves the actual radon concentration unaffected, reduces the ER, and therefore, reduces the risk associated with the SLRDs.  Thus burning a candle has no effect on the steady-state radon concentration in an house, but significantly reduces the ER of unattached faction. 

Simply running a Casablanca-Type ceiling fan in a house can result in a 90% reduction of unattached SLRDs. 

Pilot lights are typically vented directly to the outdoors, and generally run pretty clean and unless it is burning fuel rich, doesn’t produce a lot of UFPs.  A stove top will create significant convection currents and will increase the mixing factor in a room, encouraging plate-out.  A wood burning stove also increases air movement through convection and often has a force air fan that even further increases air movement, thus further inducing plate out.  Virtually all of the “radon” measurement systems ignore the actual ER and, if memory serves me correctly, the calculations used by most labs is for an assumed ER or 0.5 when calculating the (otherwise bogus) “pCi/l of radon.”

I hope that all makes sense.

Well that's all very complex and to solve it without solving the groundwater part which creates the opportunity to foul the air in the home seems rather shortsighted and expensive for what you get to me.

By sealing off the entire foundation and soils contained there for thermal reasons matches what's done for groundwater problems, so the only added thing is insulation and radon as a concern is covered with the ROI space & water heating for about triple just doing the radon mitigation.

Being off-grid is way cheaper today & easier to install systems than it used to be, makes no sense to have to handle radon alone when a home requires what's essentially groundwater management methods to mitigate it.

Makes total sense! Thanks again Caoimhín for the very detailed information. I think I'm getting a pretty good understanding on the whole Radon hype now. Thanks for the science! I love science!


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