unfortunately, thats what the rule book wants you to have its for accidents in the pit & camping area (which are more likely to be caused by bar-b-q's than anything else)
I've just spoken to Eddie at the ACU who confirms that the word 'powder' has been removed from the next handbook as the had complaints that they were difficult to get hold of. A foam one would be perfectly acceptable.
I can't find any cheaper than UDs £23.75 so I'll bag one of those if there's any left!