After my walk over Moel Famau and Moel Arthur I was looking forward to making a hot drink. My brew kit lives permanently in the boot of the truck, so I don't forget to take it with me! I unpacked my Primus Gravity stove from its pouch and connected up a gas cylinder.
I use a Light My Fire Swedish Fire Steel rather than matches or a lighter. This will generate a spark under almost any conditions and doesn't run out of gas, or refuse to light when soggy, like lighters and, matches. I keep it in a small zipped section of the pouch that the stove lives in. I pulled it out, so I coud light the stove and noticed that the steel was now only about half an inch long! I thought that it must have somehow got broken, but looking inside the pouch there was nothing but a pile of grey dust. Luckily there was just enough left to generate a spark and light my stove.
When I got home I spent some time Googling and found that other people had had similar problems: here and there was a possible explanation . It would appear that contact with inorganic salts and water can make the fire steel, which is made from an alloy called Ferrocerium, can act as a battery. This results in the fire steel corroding away. The bag containing my steel may well have been slightly damp, but as far as I know it hadn't come into contact with any salt solutions unless something spilt on the bag had soaked through.
Anyway, lesson learned. Always check your fire steel before setting out. Even something you think couldn't possibly fail can do so in an unexpected way.