& is used with permission.
The thing is, humidity is a fact of life here in Florida for 6-9 months out of the year, and so it's important to realize that things can rust just from the humidity itself. As I write this article, it's 79° F and 64% humidity outdoors, and it just so happens that iron rusts at 50% humidity or greater, and steel rusts at 80%.
In fact, just leaving a metal knife in your car can be a bad thing. As the sun heats the interior, the metal will stay cooler than the air, and moisture will condense on the cool metal surface. In fact, that's likely what happened here:
Incidentally, this is why I recommend stainless steels for get-home bag knives: they are far less likely to rust in storage than carbon steels. I do make an exception for those blade which have a baked-on coating over the metal (like what is on my Cold Steel Kukri Machete), because they are protected over 90% of their surface.
- Check your metal tools for rust on a regular basis, even if you think they're protected.
- Use WD-40 to displace any moisture, but be warned it dries quickly and doesn't protect well.
- Cover bare metal with a protective oil. I prefer Breakfree CLP, but there are many excellent choices out there.
- More information about rust, its removal and prevention can be found in this PDF. I advise all readers to read it, save it, and keep it in their list of prepping articles.