A normal smoke grenade is about the size of and is shaped like a beer can. A white phosphorus or WP grenade is shaped different and is heavier. It looks nothing like a common smoke grenade and it is next to impossible to mistake one for the other. The WP called Willy Peter by the troops is a very special smoke grenade and is only used when necessary. It has a bursting radius of twenty five meters and showers that area with burning white phosphorus and produces an extremely thich cloud of billowing white smoke.
Nothing puts it out.
It will burn right through a person unless it is pried out with a stick or falls out from gravity. In short it is quite nasty. Unlike a smoke grenade which has an instantaneous fuse, a WP grenade has a delayed fuze like a fragmentation grenade. When the WP didn't pop like a normal smoke grenade, Top kicked it and it exploded in his face. An infantryman would not have made that mistake in the dark much less in broad daylight.