When I was a kid, I remember opening up a smoke detector and finding the international symbol for radiation printed on its innards.
I knew that nuclear power plants, nuclear weapons and Spiderman all used radiation. But really, a smoke detector? Was that true, or was there some kind of printing error?
It turns out that a surprising number of everyday items use nuclear radiation to do their jobs, or are inherently radioactive. Here’s a short list of everyday items that are surprisingly radioactive--and what that radiation means for you.
Smoke Detectors
Yes, many smoke detectors really are radioactive. According to the United States Forest Service, there are two main kinds of smoke detectors: photoelectric detectors, and ionization chamber detectors.
Ionization chamber detectors contain a small amount of the radioactive element americium-241. During normal operations, the element sends out radioactive particles which travel through a chamber in the device and hit a sensor, generating a tiny electrical current. If the device’s chamber fills with smoke, the smoke particles disrupt the radioactive particles, reducing the current. The detector knows there’s a fire, and the alarm sounds.
Photoelectric smoke detectors work much the same way, but they use light instead of radioactivity in order to detect smoke. This works well too, but ionization chamber smoke detectors are extremely sensitive, allowing them to respond to the smoke from slow-burning fires. For that reason, they’re still used in many facilities and homes today, despite their radioactivity.
That warning I saw as a kid, it turns out, wasn’t a misprint after all.
Exit Signs
Many emergency exit signs use glow-in-the-dark tape or small electric lights in order to stay illuminated and direct people to safety even when the power goes out. But some exit signs use a different approach.
Tritium exit signs contain small tubes filled with the gas tritium, which is a mildly radioactive form of hydrogen. According to the Environmental Protection Agency, the tritium tubes give off a small amount of radioactivity continuously, which causes a special coating on the tubes to glow. That allows tritium exit signs to be a “self-powered light source”, and to stay illuminated indefinitely, even after days without electric power.
The signs are also helpful in facilities where it’s not easy to run new electrical wiring. Because they don’t require an external power source, they can be installed above doors in the far corners of a building without the need to call in an electrician, install expensive battery backups, and the like. Thanks to its radioactivity, a well-designed tritium exit sign will shine for 10+ years with no maintenance.
Watch Dials
How do you get the numerals, hands and other elements of an analog watch face to glow at night, so that the wearer can check the time even in the dark? Today, most watches either use electrically-lit dials, or make use of a fluorescent materials which glows in the dark, much like those little stars people stuck on kids’ ceilings in the 1990s.
Much earlier, though, many watches used a different material: radium. According to Bloomberg, many watches and clocks from the early 20th century onward used radium paint to make their dials glow. The paint is self luminous — radium’s radioactivity causes phosphor in the paint to glow a greenish color, even without an external power source.
There are several problems with radium paint, though. Over time, it tends to lose its glow, as radium’s decay products disrupt other pigments in the paint. It also releases radon gas, which can be highly radioactive and potentially harmful. And tragically, applying radium paint is extremely dangerous for workers. Radium paint was often applied by young women — known later as “radium girls” — many of whom went on to develop various cancers. Thankfully, radium paint has been largely phased on out in new timepieces, but it still may be present in heirloom ones.
Antique Glass
Glassmakers used to use all kinds of potentially harmful additives to give decorative vases, cups and other glassware dramatic colors, including heavy metals like lead. But uranium glass (later known as Vaseline glass) takes the cake. According to Collector’s Weekly, these delicate glass products were colored with uranium, giving them a vibrant, light-green color.
Most uranium glass dates to the 1930s through 1950s, so you’re unlikely to encounter it unless you go antiquing. Collectors apparently cherish it for its unique color, as well as the fact that it fluoresces brilliantly under a black light.
Uranium glass does release a bit of radiation, but Collector’s Weekly says studies suggest that it’s likely harmless to most users — even if one were to drink from a uranium glass cup. Would I personally drink from an antique glass colored with the same stuff used to build an atom bomb? Probably not. The EPA says you shouldn’t drink or eat from these vessels, as radioactive parts can chip off and enter your body.
Bananas
Yes, you read that right. Bananas are mildly radioactive. The yellow fruit is healthy in part because bananas contain lots of potassium. But according to Science Focus, a portion of that potassium is the isotope potassium-40, which emits radiation.
Does that mean bananas are harmful? No. According to McGill University, if you ate 1,000 bananas, you’d increase your risk of a radiation-related death by 1 in 1,000,000. Put differently, you’d have to ingest 1 billion bananas before their radiation would cause certain death.
Bananas' radiation can cause other problems, though. According to the BBC, shipping containers filled with bananas can sometimes trigger radiation detectors at ports, prompting fears of a radiological attack or a smuggled nuclear weapon. Nena would be proud.
What does all this radioactivity mean for you, the consumer? In most cases, not too much. The majority of these radioactive items--with the exception of some watch dials--are perfectly safe during everyday use. For some, hazards only emerge when you go to throw them away.
Right to Repair is great for many gadgets, but the EPA says that if you have an ionization smoke detector. you should never open it up or tamper with it. (As a kid, I immediately stopped messing with the one I found once I saw the radiation symbol). Otherwise, you can safely throw it in your household trash when it’s reached the end of its useful life.
When it comes to tritium exit signs, things are a little more complex. The Nuclear Regulatory Commission says you should never dispose of these signs in normal trash. To safely get rid of one, you must “transfer the sign to a specific licensee — such as a manufacturer, distributor, licensed radioactive waste broker or licensed low-level radioactive waste disposal facility” and then file a report to the NRC within 30 days.
According to the EPA, radium watches are usually safe, as long as they’re in good condition and intact. One thing to keep in mind — if your older watch originally had a radium dial, it may no longer glow, but it’s likely still radioactive. For that reason, it’s best to check with a watch repair professional or a collectors’ organization if you have an old watch which is broken, since any watch from the early 20th century could potentially contain radium. If you need to throw away an old watch or some uranium glass, contact your state’s radiation control division.