the cold glow of tritium

I have been slowly working on a book. Don't get too excited, it is on a very niche topic and I will probably eventually barely finish it and then post it here. But in the mean time, I will recount some stories which are related, but don't quite fit in. Today, we'll learn a bit about the self-illumination industry.

At the turn of the 20th century, it was discovered that the newfangled element radium could be combined with a phosphor to create a paint that glowed. This was pretty much as cool as it sounds, and commercial radioluminescent paints like Undark went through periods of mass popularity. The most significant application, though, was in the military: radioluminescent paints were applied first to aircraft instruments and later to watches and gunsights. The low light output of radioluminescent paints had a tactical advantage (being very difficult to see from a distance), while the self-powering nature of radioisotopes made them very reliable.

The First World War was thus the "killer app" for radioluminescence. Military demand for self-illuminating devices fed a "radium rush" that built mines, processing plants, and manufacturing operations across the country. It also fed, in a sense much too literal, the tragedy of the "Radium Girls." Several self-luminous dial manufacturers knowingly subjected their women painters to shockingly irresponsible conditions, leading inevitably to radium poisoning that disfigured, debilitated, and ultimately killed. Today, this is a fairly well-known story, a cautionary tale about the nuclear excess and labor exploitation of the 1920s. That the situation persisted into the 1940s is often omitted, perhaps too inconvenient to the narrative that a series of lawsuits, and what was essentially the invention of occupational medicine, headed off the problem in the late 1920s.

What did happen after the Radium Girls? What was the fate of the luminous radium industry?

A significant lull in military demand after WWI was hard on the radium business, to say nothing of a series of costly settlements to radium painters despite aggressive efforts to avoid liability. At the same time, significant radium reserves were discovered overseas, triggering a price collapse that closed most of the mines. The two largest manufacturers of radium dials, Radium Dial Company (part of Standard Chemical who owned most radium mines) and US Radium Corporation (USRC), both went through lean times. Fortunately, for them, the advent of the Second World War reignited demand for radioluminescence.

The story of Radium Dial and USRC doesn't end in the 1920s---of course it doesn't, luminous paints having had a major 1970s second wind. Both companies survived, in various forms, into the current century. In this article, I will focus on the post-WWII story of radioactive self-illumination and the legacy that we live with today.

During its 1920s financial difficulties, the USRC closed the Orange, New Jersey plant famously associated with Radium Girls and opened a new facility in Brooklyn. In 1948, perhaps looking to manage expenses during yet another post-war slump, USRC relocated again to Bloomsburg, Pennsylvania. The Bloomsburg facility, originally a toy factory, operated through a series of generational shifts in self-illuminating technology.

The use of radium, with some occasional polonium, for radioluminescence declined in the 1950s and ended entirely in the 1970s. The alpha radiation emitted by those elements is very effective in exciting phosphors but so energetic that it damages them. A longer overall lifespan, and somewhat better safety properties, could be obtained by the use of a beta emitter like strontium or tritium. While strontium was widely used in military applications, civilian products shifted towards tritium, which offered an attractive balance of price and half life.

USRC handled almost a dozen radioisotopes in Bloomsburg, much of them due to diversified operations during the 1950s that included calibration sources, ionizers, and luminous products built to various specific military requirements. The construction of a metal plating plant enabled further diversification, including foil sources used in research, but eventually became an opportunity for vertical integration. By 1968, USRC had consolidated to only tritium products, with an emphasis on clocks and watches.

Radioluminescent clocks were a huge hit, in part because of their practicality, but fashion was definitely a factor. Millions of radioluminescent clocks were sold during the '60s and '70s, many of them by Westclox. Westclox started out as a typical clock company (the United Clock Company in 1885), but joined the atomic age through a long-lived partnership with the Radium Dial Company. The two companies were so close that they became physically so: Radium Dial's occupational health tragedy played out in Ottawa, Illinois, a town Radium Dial had chosen as its headquarters due to its proximity to Westclox in nearby Peru [1].

Westclox sold clocks with radioluminescent dials from the 1920s to probably the 1970s, but one of the interesting things about this corner of atomic history is just how poorly documented it is. Westclox may have switched from radium to tritium at some point, and definitely abandoned radioisotopes entirely at some point. Clock and watch collectors, a rather avid bunch, struggle to tell when. Many consumer radioisotopes are like this: it's surprisingly hard to know if they even are radioactive.

Now, the Radium Dial Company itself folded entirely to a series of radium poisoning lawsuits in the 1930s. Simply being found guilty of one of the most malevolent labor abuses of the era would not stop free enterprise, though, and Radium Dial's president founded a legally distinct company called Luminous Processes just down the street. Luminous Processes is particularly notable for having continued the production of radium-based clock faces until 1978, making them the last manufacturer of commercial radioluminescent radium products. This also presents compelling circumstantial evidence that Westclox continued to use radium paint until sometime around 1978, which lines up with the general impressions of luminous dial collectors.

While the late '70s were the end of Radium Dial, USRC was just beginning its corporate transformation. From 1980 to 1982, a confusing series of spinoffs and mergers lead to USR Industries, parent company of Metreal, parent company of Safety Light Corporation, which manufactured products to be marketed and distributed by Isolite. All of these companies were ultimately part of USR Industries, the former USRC, but the org chart sure did get more complex. The Nuclear Regulatory Commission expressed some irritation in their observation, decades later, that they weren't told about any of this restructuring until they noticed it on their own.

Safety Light, as expressed by the name, focused on a new application for tritium radioluminescence: safety signage, mostly self-powered illuminated exit signs and evacuation signage for aircraft. Safety Light continued to manufacture tritium exit signs until 2007, when they shut down following some tough interactions with the NRC and the EPA. They had been, in the fashion typical of early nuclear industry, disposing of their waste by putting it in a hole in the ground. They had persisted in doing this much longer than was socially acceptable, and ultimately seem to have been bankrupted by their environmental obligations... obligations which then had to be assumed by the Superfund program.

The specific form of illumination used in these exit signs, and by far the most common type of radioluminescence today, is the Gaseous Tritium Light Source or GTLS. GTLS are small glass tubes or vials, usually made with borosilicate glass, containing tritium gas and an internal coating of phosphor. GTLS are simple, robust, and due to the very small amount of tritium required, fairly inexpensive. They can be made large enough to illuminate a letter in an exit sign, or small enough to be embedded into a watch hand. Major applications include watch faces, gun sights, and the keychains of "EDC" enthusiasts.

Plenty of GTLS manufacturers have come and gone over the years. In the UK, defense contractor Saunders-Roe got into the GTLS business during WWII. Their GTLS product line moved to Brandhurst Inc., which had a major American subsidiary. It is an interesting observation that the US always seems to have been the biggest market for GTLS, but their manufacture has increasingly shifted overseas. Brandhurst is no longer even British, having gone the way of so much of the nuclear world by becoming Canadian. A merger with Canadian company SRB created SRB Technologies in Pembroke, Ontario, which continues to manufacture GTLS today.

Other Canadian GTLS manufacturers have not fared as well. Shield Source Inc., of Peterborough, Ontario, began filling GTLS vials in 1987. I can't find a whole lot of information on Shield Source's early days, but they seem to have mostly made tubes for exit signs, and perhaps some other self-powered signage. In 2012, the Canadian Nuclear Safety Commission (CNSC) detected a discrepancy in Shield Source's tritium emissions monitoring. I am not sure of the exact details, because CNSC seems to make less information public in general than the US NRC [2].

Here's what appears to have happened: tritium is a gas, which makes it tricky to safely handle. Fortunately, the activity of tritium is relatively low and its half life is relatively short. This means that it's acceptable to manage everyday leakage (for example when connecting and disconnecting things) in a tritium workspace by ventilating it to a stack, releasing it to the atmosphere for dilution and decay. The license of a tritium facility will specify a limit for how much radioactivity can be released this way, and monitoring systems (usually several layers of monitoring systems) have to be used to ensure that the permit limit is not exceeded. In the case of Shield Source, some kind of configuration error with the tritium ventilation monitoring system combined with a failure to adequately test and audit it. The CNSC discovered that during 2010 and 2011, the facility had undercounted their tritium emissions, and in fact exceeded the limits of their license.

Air samplers located around the facility, some of which were also validated by an independent laboratory, did not detect tritium in excess of the environmental limits. This suggests that the excess releases probably did not have an adverse impact on human health or the environment. Still, exceeding license terms and then failing to report and correct the problem for two years is a very serious failure by a licensee. In 2012, when the problem was discovered, CNSC ordered Shield Source's license modified to prohibit actual tritium handling. This can seem like an odd maneuver but something similar can happen in the US. Just having radioisotope-contaminated equipment, storing test sources, and managing radioactive waste requires a license. By modifying Shield Source's license to prohibit tritium vial filling, the CNSC effectively shut the plant down while allowing Shield Source to continue their radiological protection and waste management functions. This is the same reason that long-defunct radiological facilities often still hold licenses from NRC in the US: they retain the licenses to allow them to store and process waste and contaminated materials during decommissioning.

In the case of Shield Source, while the violation was serious, CNSC does not seem to have anticipated a permanent shutdown. The terms agreed in 2012 were that Shield Source could regain a license to manufacture GTLS if it produced for CNSC a satisfactory report on the root cause of the failure and actions taken to prevent a recurrence. Shield Source did produce such a report, and CNSC seems to have mostly accepted it with some comments requesting further work (the actual report does not appear to be public). Still, in early 2013, Shield Source informed CNSC that it did not intend to resume manufacturing. The license was converted to a one-year license to facilitate decommissioning.

Tritium filling and ventilation equipment, which had been contaminated by long-term exposure to tritium, was "packaged" and disposed. This typically consists of breaking things down into parts small enough to fit into 55-gallon drums, "overpacking" those drums into 65-gallon drums for extra protection, and then coordinating with transportation authorities to ship the materials in a suitable way to a facility licensed to dispose of them. This is mostly done by burying them in the ground in an area where the geology makes groundwater interaction exceedingly unlikely, like a certain landfill on the Texas-New Mexico border near Eunice. Keep in mind that tritium's short half life means this is not a long-term geological repository situation; the waste needs to be safely contained for only, say, fifty years to get down to levels not much different from background.

I don't know where the Shield Source waste went, CNSC only says it went to a licensed facility. Once the contaminated equipment was removed, drywall and ceiling and floor finishes were removed in the tritium handling area and everything left was thoroughly cleaned. A survey confirmed that remaining tritium contamination was below CNSC-determined limits (for example, in-air concentrations that would lead to a dose of less than 0.01 mSv/year for 9-5 occupational exposure). At that point, the Shield Source building was released to the landlord they had leased it from, presumably to be occupied by some other company. Fortunately tritium cleanup isn't all that complex.

You might wonder why Shield Source abruptly closed down. I assume there was some back-and-forth with CNSC before they decided to throw in the towel, but it is kind of odd that they folded entirely during the response to an incident that CNSC seems to have fully expected them to survive. I suspect that a full year of lost revenue was just too much for Shield Source: by 2012, when all of this was playing out, the radioluminescence market had seriously declined.

There are a lot of reasons. For one, the regulatory approach to tritium has become more and more strict over time. Radium is entirely prohibited in consumer goods, and the limit on tritium activity is very low. Even self-illuminating exit signs now require NRC oversight in the US, discussed shortly. Besides, public sentiment has increasingly turned against the Friendly Atom is consumer contexts, and you can imagine that people are especially sensitive to the use of tritium in classic institutional contexts for self-powered exit signs: schools and healthcare facilities.

At the same time, alternatives have emerged. Non-radioactive luminescent materials, the kinds of things we tend to call "glow in the dark," have greatly improved since WWII. Strontium aluminate is a typical choice today---the inclusion of strontium might suggest otherwise, but strontium aluminate uses the stable natural isotope of strontium, Sr-88, and is not radioactive. Strontium aluminate has mostly displaced radioluminescence in safety applications, and for example the FAA has long allowed it for safety signage and path illumination on aircraft. Keep in mind that these luminescent materials are not self-powered. They must be "charged" by exposure to light. Minor adaptations are required, for example a requirement that the cabin lights in airliners be turned on for a certain period of time before takeoff, but in practice these limitations are considered preferable to the complexity and risks involved in the use of radioisotopes.

You are probably already thinking that improving electronics have also made radioluminescence less relevant. Compact, cool-running, energy-efficient LEDs and a wide variety of packages and form factors mean that a lot of traditional applications of radioluminescence are now simply electric. Here's just a small example: in the early days of LCD digital watches, it was not unusual for higher-end models to use a radioluminescent source as a backlight. Today that's just nonsensical, a digital watch needs a power source anyway and in even the cheapest Casios a single LED offers a reasonable alternative. Radioluminescent digital watches were very short lived.

Now that we've learned about a few historic radioluminescent manufacturers, you might have a couple of questions. Where were the radioisotopes actually sourced? And why does Ontario come up twice? These are related. From the 1910s to the 1950s, radioluminescent products were mostly using radium sourced from Standard Chemical, who extracted it from mines in the Southwest. The domestic radium mining industry collapsed by 1955 due to a combination of factors: declining demand after WWII, cheaper radium imported from Brazil, and a broadly changing attitude towards radium that lead the NRC to note in the '90s that we might never again find the need to extract radium: radium has a very long half life that makes it considerably more difficult to manage than strontium or tritium. Today, you could say that the price of radium has gone negative, in that you are far more likely to pay an environmental management company to take it away (at rather high prices) than to buy more.

But what about tritium? Tritium is not really naturally occurring; there technically is some natural tritium but it's at extremely low concentrations and very hard to get at. But, as it happens, irradiating water produces a bit of tritium, and nuclear reactors incidentally irradiate a lot of water. With suitable modifications, the tritium produced as a byproduct of civilian reactors can be concentrated and sold. Ontario Hydro has long had facilities to perform this extraction, and recently built a new plant at the Darlington Nuclear Station that processes heavy water shipped from CANDU reactors throughout Ontario. The primary purpose of this plant is to reduce environmental exposure from the release of "tritiated" heavy water; it produces more tritium than can reasonably be sold, so much of it is stored for decay. The result is that tritium is fairly abundant and cheap in Ontario.

Besides SRB Technologies which packages tritium from Ontario Hydro into GTLS, another major manufacturer of GTLS is the Swiss company mb-microtec. mb-microtec is the parent of watch brand Traser and GTLS brand Trigalight, and seem to be one of the largest sources of consumer GTLS overall. Many of the tritium keychains you can buy, for example, use tritium vials manufactured by mb-microtec. NRC documents suggest that mb-microtec contracts a lot of their finished product manufacturing to a company in Hong Kong and that some of the finished products you see using their GTLS (like watches and fobs) are in fact white-labeled from that plant, but unfortunately don't make the original source of the tritium clear. mb-microtec has the distinction of operating the only recycling plant for tritium gas, and press releases surrounding the new recycling operation say they purchase the rest of their tritium supply. I assume from the civilian nuclear power industry in Switzerland, which has several major reactors operating.

A number of other manufacturers produce GTLS primarily for military applications, with some safety signage side business. And then there is, of course, the nuclear weapons program, which consumes the largest volume of tritium in the US. The US's tritium production facility for much of the Cold War actually shut down in 1988, one of the factors in most GTLS manufacturers being overseas. In the interim period, the sole domestic tritium supply was recycling of tritium in dismantled weapons and other surplus equipment. Since tritium has such a short half-life, this situation cannot persist indefinitely, and tritium production was resumed in 2004 at the Tennessee Valley Authority's Watts Bar nuclear generating station. Tritium extracted from that plant is currently used solely by the Department of Energy, primarily for the weapons program.

Finally, let's discuss the modern state of radioluminescence. GTLS, based on tritium, are the only type of radioluminescence available to consumers. All importation and distribution of GTLS requires an NRC license, although companies that only distribute products that have been manufactured and tested by another licensee fall under a license exemption category that still requires NRC reporting but greatly simplifies the process. Consumers that purchase these items have no obligations to the NRC. Major categories of devices under these rules include smoke detectors, detection instruments and small calibration sources, and self-luminous products using tritium, krypton, or promethium. You might wonder, "how big of a device can a I buy under these rules?" The answer to that question is a bit complicated, so let me explain my understanding of the rules using a specific example.

Let's say you buy a GTLS keychain from massdrop or wherever people get EDC baubles these days [3]. The business you ordered it from almost certainly did not make it, and is acting as an NRC exempt distributor of a product. In NRC terms, your purchase of the product is not the "initial sale or distribution," that already happened when the company you got it from ordered it from their supplier. Their supplier, or possibly someone further up in the chain, does need to hold a license: an NRC specific license is required to manufacture, process, produce, or initially transfer or sell tritium products. This is the reason that overseas companies like SRB and mb-microtec hold NRC licenses; this is the only way for consumers to legally receive their products.

It is important to note the word "specific" in "NRC specific license." These licenses are very specific; the NRC approves each individual product including the design of the containment and and labeling. When a license is issued, the individual products are added to a registry maintained by the NRC. When evaluating license applications, the NRC considers a set of safety objectives rather than specific criteria. For example, and if you want to read along we're in 10 CFR 32.23:

In normal use and disposal of a single exempt unit, it is unlikely that the external radiation dose in any one year, or the dose commitment resulting from the intake of radioactive material in any one year, to a suitable sample of the group of individuals expected to be most highly exposed to radiation or radioactive material from the product will exceed the dose to the appropriate organ as specified in Column I of the table in § 32.24 of this part.

So the rules are a bit soft, in that a licensee can argue back and forth with the NRC over means of calculating dose risk and so on. It is, ultimately, the NRC's discretion as to whether or not a device complies. It's surprisingly hard to track down original licensing paperwork for these products because of how frequently they are rebranded, and resellers never seem to provide detailed specifications. I suspect this is intentional, as I've found some cases of NRC applications that request trade secret confidentiality on details. Still, from the license paperwork I've found with hard numbers, it seems like manufacturers keep the total activity of GTLS products (e.g. a single GTLS sold alone, or the total of the GTLS in a watch) under 25 millicurie.

There do exist larger devices, of which exit signs are the largest category. Self-powered exit signs are also manufactured under NRC specific licenses, but their activity and resulting risk is too high to qualify for exemption at the distribution and use stage. Instead, all users of self-powered safety signs do so under a general license issued by the NRC (a general license meaning that it is implicitly issued to all such users). The general license is found in 10 CFR 31. Owners of tritium exit signs are required to designate a person to track and maintain the signs, inform the NRC of that person's contact information and any changes in that person, to inform the NRC of any lost, stolen, or damaged signs. General licensees are not allowed to sell or otherwise transfer tritium signs, unless they are remaining in the same location (e.g. when a building is sold), in which case they must notify the NRC and disclose NRC requirements to the transferee.

When tritium exit signs reach the end of their lifespan, they must be disposed of by transfer to an NRC license holder who can recycle them. The general licensee has to notify the NRC of that transfer. Overall, the intent of the general license regulations is to ensure that they are properly disposed of: reporting transfers and events to the NRC, along with serial numbers, allows the NRC to audit for signs that have "disappeared." Missing tritium exit signs are a common source of NRC event reports. It should also be said that, partly for these reasons, tritium exit signs are pretty expensive. Roughly $300 for a new one, and $150 to dispose of an old one.

Other radioluminescent devices you will find are mostly antiques. Radium dials are reasonably common, anything with a luminescent dial made before, say, 1960 is probably radium, and specifically Westclox products to 1978 likely use radium. The half-life of radium-226 is 1,600 years, so these radium dials have the distinction of often still working, although the paints have usually held up more poorly than the isotopes they contain. These items should be handled with caution, since the failure of the paint creates the possibility of inhaling or ingesting radium. They also emit radon as a decay product, which becomes hazardous in confined spaces, so radium dials should be stored in a well-ventilated environment.

Strontium-90 has a half-life of 29 years, and tritium 12 years, so vintage radioluminescent products using either have usually decayed to the extent that they no longer shine brightly or even at all. The phosphors used for these products will usually still fluoresce brightly under UV light and might even photoluminesce for a time after light exposure, but they will no longer stay lit in a dark environment. Fortunately, the decay that makes them not work also makes them much safer to handle. Tritium decays to helium-3 which is quite safe, strontium-90 to yttrium-90 which quickly decays to zirconium-90. Zirconium-90 is stable and only about as toxic as any other heavy metal. You can see why these radioisotopes are now much preferred over radium.

And that's the modern story of radioluminescence. Sometime soon, probably tomorrow, I will be sending out my supporter's newsletter, EYES ONLY, with some more detail on environmental remediation at historic processing facilities for radioluminescent products. You can learn a bit more about how US Radium was putting their waste in a hole in the ground, and also into a river, and sort of wherever else. You know Radium Dial Company was up to similar abuses.

[1] The assertion that Ottawa is conveniently close to Peru is one of those oddities of naming places after bigger, more famous places.

[2] CNSC's whole final report on Shield Source is only 25 pages. A similar decommissioning process in the US would produce thousands of pages of public record typically culminating in EPA Five Year Reviews which would be, themselves, perhaps a hundred pages depending on the amount of post-closure monitoring. I'm not familiar with the actual law but it seems like most of the difference is that CNSC does not normally publish technical documentation or original data (although one document does suggest that original data is available on request). It's an interesting difference... the 25-page report, really only 20 pages after front matter, is a lot more approachable for the public than a 400 page set of close-out reports. Much of the standard documentation in the US comes from NEPA requirements, and NEPA is infamous in some circles for requiring exhaustive reports that don't necessarily do anything useful. But from my perspective it is weird for the formal, published documentation on closure of a radiological site to not include hydrology discussion, demographics, maps, and fifty pages of data tables as appendices. Ideally a bunch of one-sentence acceptance emails stapled to the end for good measure. When it comes to describing the actual problem, CNSC only gives you a couple of paragraphs of background.

[3] Really channeling Guy Debord with my contempt for keychains here. during the writing of this article, I bought myself a tritium EDC bauble, so we're all in the mud together.