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One day, I was looking up at an EXIT sign over a door, and noticed a "Caution: Radioactive" sticker on it. I got on a chair and read the label, and found that the glowing EXIT sign was powered by tritium (a radioactive isotope of hydrogen). The exit sign contained 14 Curies of radioactivity (This is one of the many units used to describe levels of radio-activity).

Our lab might transact about 3 microcuries in a week (a microcurie is, naturally, one one-millionth of a Curie). While it was a small lab, I'd imagine that the entire research building may take in as much as 4 millicuries a month (four-thousandths of a Curie), so one EXIT sign has about three thousand months of radioactivity in it.

Of course, it was a 3-story building with stairwell exits on each end (six EXIT signs), plus another 2-story research wing (four EXIT signs) and an office area (four more), making a total of 14 signs at 14 Curies each. That amounts to about a quarter kiloton or so (Just joking!).

In the event of a fire, the least of the worries would be the release of the miniscule amount of research-related radioactivity in the building. I wonder if the EXIT signs were to be discarded in the regular trash when they were to be replaced?

In fairness, I must say that the radioactive phosphorus that we used is "sticky" compared with other chemical tracers. It tends to adhere to other things and also react with other chemicals, making it more likely to get caught in your body. Also, since it is in the form of a DNA component, it can be metabolized and incorporated into your body to a small degree. Tritium, on the other hand, is much more inert. It would most likely burn up in a fire, becoming incorporated into water molecules and dispersing into the environment. This would dilute its effects to insignificance. Still, the difference in handling rules for EXIT signs vs radioactive tracers is amazing.

...
Don't get me started about the janitor who set off alarms because she was given a Technicium tracer at the local hospital; or the radio-iodine laden cat poop that was caught at the landfill.

--TwoDragons

Makes me nervous.