Radiation Safety vs Driving Safety

There is a Commentary in the latest issue of the Health Physics Journal about foregoing the Linear No Threshold (LNT) dose model for cancer risk assessment. The authors agree it is sound to use LNT for radiation protection regulation purposes, however.

So the authors basically are LNT-deniers and employ many of the denialist arguments I've blogged about before.

The commentary is a bit odd in that the authors reference BEIR VII at the outset. BEIR VII was undertaken by the National Academy of Sciences in order to determine which dose model best represents radiation dose data. They concluded LNT. Yet the authors make arguments which were already addressed in BEIR VII.

The authors frequently reference the Health Physics Society (HPS) position paper on radiation risk to support their position.  But even though this paper was revised in 2010 (giving it a sense of modernity), you can see that it is based on NCRP Report 126, which was written in 1997!  The NCRP reviewed the applicability of the LNT model in 2001, in Report 136.  Here is a copy and paste from its Preface:

"In developing its basic radiation protection recommendations, as given in NCRP Report No. 116, Limitation of Exposure to Ionizing(NCRP, 1993a), the Council reiterated its acceptance of the linear-nonthreshold hypothesis for the risk-dose relationship."

So the HPS is either cherry picking NCRP reports (which wouldn't be intellectually honest unless they exposed flaws in certain reports) or its paper simply isn't up to date (that's my guess, since the HPS has volunteer members around the country with no centralized bureaucracy).

The only other point I want to cover in this post is related to the post's title.  The Commentary authors compare driving safety to radiation safety. They state that drivers are not forced to drive less than some arbitrary annual mileage limit, subject to further "ALARA" restrictions, even though the risks of death are comparable (10 miles driven poses about the same risk as about 1 mrem of dose).  Note that "ALARA" stands for As Low As Reasonably Achievable, which is a philosophical (and regulatory) view that doses should be kept as low as reasonably achievable..

I've more frequently heard this comparison phrased differently.  Something like, "If ALARA was applied to driving, everyone would be forced to drive as slow as reasonably achievable.  Since we don't do that, ALARA is an unsound view".

Both versions are overly simplistic representations.  In the former case, cancer is more highly associated with total dose not dose rate.  So the limit is in terms of total dose.  Death due to driving is more highly associated with speed and human reaction time, not total driving distance.  So the radiation limit is in terms of total dose, regardless of dose rate (even though the total dose limit is an annual limit, which limits the dose rate on an annual basis).   And the speed limit is in terms of distance rate (speed), regardless of total distance (even though the total annual distance travelled is limited by the speed limit). So drivers actually do have a limit on how far they can drive in a year, and it depends on the route they choose to take.
 
In considering the latter case, people are forced to drive as slow as reasonable.  The National Highway Transportation Safety Administration Basic Speed Rule is:

"No person shall drive a vehicle greater than is reasonable and prudent under the conditions and having regard to the actual and potential hazards then existing." (emphasis mine)

You can't drive the speed limit when there is slowed traffic ahead, or kids in the road, or icy conditions, etc.  It is only in the absence of such circumstances that one can drive the speed limit.  Similarly, it is in the absence of alternative circumstance (ability to reasonably implement less time near radiation source, more distance from it or greater intervening shielding, etc.) that one can utilize the dose limits.

So, contrary to many claims, radiation safety and driving safety are considered and implemented very similarly.  LNT is applicable to both issues.

But there exists a threshold which is also applicable to both issues.

That would be an energy threshold.

If radiation energy falls below the lower ultraviolet range, it is no longer cancer inducing.

If people drive very slowly, there won't be sufficient kinetic energy to cause death in the event of a collision.