Having worked at UL in their fire testing dept for almost a decade & for the ERT at Amoco Research Center for over a decade, i do serious question that Shell Oil would have recommended utilizing wet towel in the last quarter century...but if there really is a document from them...well...
there are 3 very obvious reason I can see why NOT to recommend the use of a wet towel for a kithchen fire
1. Many kitchen fires are grease/oil & a wet towel could spread, father than diminish, a grease/oil fire
2. Most likely you would need to take the time to saturate a towel, while the fire is increasing, prudent fire fighting is to have equipment that is ready to use, useful for the potential fires & quick to activate
3. Waving a not-wet-enough towel near a fire would bring the fire to you, a very dangerous potential, one of the main things that fire fighter are trained to avoid!
UL & many fire dept. create PSA's on how to handle many household fire dangers, and here is one that CBS aired a few years ago:
http://www.cbsnews.com/news/how-to-handl...hen-fires/
And, if you do have an old disposable extinguisher that you have gotten a replacement for, one thing that you could do is to PRACTICE USING THE EXTINGUISHER (I would not recommend using it on real practice fire, but a mock fire of red construction paper or a stack of twigs representing a fire.. or.. anything to practice activating the extinguisher & doing the fire sweep....)
added plus, this gets the pressure out of the cylinder for better waste disposal!