White Phosphorus

Easy: "White phosphorus is only slightly soluble in water and it can be stored under water. White phosphorus is only safe from self-igniting when it is submerged in water." --Wikipedia

Also, with a 30 °C ignition temperature, being in the guy's pocket may have provided the warmth needed for self-ignition.

BTW: Phosphorous bombs are one of the most heinous and inhumane things we have invented, designed to maim with great suffering...just horrible.

Most probably the place mentioned is Peenemunde, well worth a visit if you are a world war 2 buff.

See here:-

Bombing of Peenemunde

It was actually in communist east Germany until the East collapsed in 89. I visited it in the summer of 2005, really, really interesting.....

Peenemunde was the "Space Coast, Florida or Edwards Air-force base/Area 51" of Nazi Germany. Many of their important (flying) weapons were developed and tested there, the V1 and the V2 for example.

(The V3 appears not to have been developed there, probably due to its size. See:- V3)

The Bombs often used by the Allies to stop weapon production often contained this chemical and some hit the sea and broke up or have now rusted through.

The sea has kept it cool and free of oxygen for the last 70 odd years.....now people accidentally gather it and stupidly put it in their pockets!! Now its free of water and has plenty of oxygen....

Furthermore, putting it in an ignited state back in water just makes the reaction worse! It needs to be buried in sand to extinguish it, where of course some of it survives even to this day on/under the beach, waiting for a kid with a bucket and spade......

Sadly, there is also a lot of Amber in the area, due to an underwater petrified ancient forest shedding it. The Amber and the phosphorus look very very similar to the untrained eye on the beach and occur in the same area.....which is why there are warnings in many languages along ALL of the beaches to ONLY gather Amber in a steel bucket with a layer of sand using steel tongs......children should not be allowed to even start....

Nobody reads the signs!!!

...and if you don't bother to read the signs.......DANGER!!

I personally would NEVER take any children on those beaches, ever.....the sea is also full of other chemicals as the Allies threw all of Nazi Germany's bombs, left over, all into the Baltic and made the problem even worse.

UXO all over!!!!

See here for a Nazi Sea Mine being cleared by a controlled explosion!!:-

http://www.youtube.com/watch?v=6Xlipe3qpWk

There is a crack team of German bomb disposal experts who air to remove or blow up a lot of munition each year. Sadly they had a serious accident a few years ago, they blew up a small bomb, but unknown to them a huge consignment of ordnance was hidden under it in the sand, several divers were killed if I remember correctly....I was unable to find that video.....see it on the TV.....

See also:-

http://www.spiegel.de/international/germany/two-women-injured-after-touching-wwii-phosphorus-on-german-beach-a-829516.html

http://www.spiegel.de/international/germany/dangers-of-unexploded-wwii-munitions-in-north-and-baltic-seas-a-893113.html

I hope this is interesting and explanatory enough for you.