Very good question. According to my knowledge of the product, the main thing that helps you sleep is "Valeriana Officinalis Root Extract" aka Valerian Root. It will not knock you out, such as a Tylenol PM. Actually, when I take the PM's I sleep more soundly and not wake up as often, but do not have trouble getting out of bed.
However, since you are a firefighter, I would advise to start off with 1 tablet and see how it affects your sleep. Perhaps you could take 2 tablets on your nights off, and see how it affects you. But in the end, just use common sense. Gauge it's effects on your days off, and then go from there.