Are these changes needed? Hi Jeff. I agree with you 100%. ASHRAE to residential radon isn’t apples to apples. The reason that the Canadian radon discharge clearances so closely match direct vent gas appliances is because the science of dispersion, re-entrainment and exposure are so very similar. With combustion appliance discharge we don’t see significant re-entrainment and we don’t see exceedance of acceptable carbon monoxide (CO) exposure limits indoors.
Thanks for the input Shawn. I have also sat on several guideline and national standard committees here in Canada and I agree with your comments. But in these committees decision is by consensus and may not reflect all opinions or all science. In several cases I have seen over prescriptive measures introduced due to a lack of information, fear that the best method won't get implemented properly by trades or simply an overabundance of caution. These are all good intentions when protecting health but they can also become frustrating and excessive.
It is essential to note the difference between ICI (Industrial, Commercial, Institutional) buildings and residential dwellings (i.e. houses). Industrial process exhaust and residential radon exhaust need to be looked at very differently. Yes, the attached ASHRAE document is sound environmental, mechanical, and building science engineering, but industry (i.e. residential building code) doesn’t use ASHRAE ICI standards of exhaust discharge for residential combustion appliances. Instead prescriptive clearances are provided that control adverse re-entrainment. One could try and apply the ASHRAE ICI standard to CO from combustion appliances in a residential setting as these effluents are technically covered by those standards but we don’t because those standards simply don’t apply to residential. It would be far too cumbersome, let alone unnecessary, for a mitigator to do all the math to apply ASHRAE ICI to residential.
ICI discharges need and were developed to address point of impingement (e.g. fence line) exposures for a whole host of acutely toxic substances with short term exposure limits (STEL) and ceiling limits. This is vastly different to chronicly toxic substances with long-term weighted exposure limits such as radon. Even POI concentrations for chronicly acute substances are based on 24/7 365 70 year exposure risk base. I am not saying “its only radon”, I’m saying use proper industrial hygiene science and proper building science together.
ASHRAE does mention radon in several of their standards but in my opinion these documents were never intended to deal specifically with radon but more so other acutely toxic substances. As a result they tend to confound things. The challenge, as Shawn has indicated, is that they may be general reference or even cited standards and therefore may have some legal bearing or perceived legal bearing.
As we know, and as demonstrated by Bill Broadhead and Canada NRC we don’t see radon above the action level re-entraining into buildings at the action level at 6ft (2m). Furthermore even if we did see a spike of radon at the window face or a spike of radon re-entrain into the building at or above the action level, that does not mean weighted radon levels have been exceeded and that an overexposure has or will occur. If we are overly worried about a transient episodic re-entrainment of radon we misunderstand what an average weighted exposure limit is. For example, just because you have smelled second hand smoke a few times it doesn’t mean you have been overexposed and it doesn't mean you will get lung cancer from it, the same applies to radon. I am far less worried about a tiny episodic re-entrainment of radon then I am about a system icing up because of too much exterior piping and resulting in elevated indoor radon throughout the building for a number of days or weeks.
Recently a few colleagues and I looked at an exhaust on a new construction radon system. Someone was using ASHRAE 62.1 2019 to impose a prescribed 30 ft (10m) minimum radon exhaust clearance criteria. Well this standard also permits you to calculate the required clearance instead of picking the 30 ft from the table. Well we did the math and came out with 6ft (2m) which is what the Canada NRC study and Bill Broadhead also figured out with experimentation.
We need to make sure we don’t take the word “toxic” out of context especially without an associated exposure or dose component. As Paracelsus, the father of toxicology, said “Poison is in everything, and no thing is without poison. The dosage makes it either a poison or a remedy.” In other words the dose makes the poison. And yes radiation and radon have a no threshold dose limit but let’s put it in perspective for the goal of the mitigator, our industry and this thread.
In the linked publication under the Toxic Stack Exhausts it clearly focuses on substances with rapid and acutely toxic effects (i.e. lab fume hoods and carbon monoxide from large output combustion appliances). These discharges are very different from a residential furnace, water heater or dryer or residential radon system. This takes us back to Jeff's comment above about the Canadian radon discharge clearance matching the gas appliance discharge clearance which matches Bill and NRC findings. Coincidence.......I think not. LOL