Class D Fires are made up of Metals that burn - Magnesium, Titanium, Aluminum
The Seattle Fire Department set out 8 magnesium engine blocks and tested several different products to see how well they worked on magnesium. Novacool is highlighted in this video. Novacool extinguishes Class D fires in un-confined spaces. Extinguishing magnesium and other metals fires (lithium) could result in the release of hydrogen from the water, creating an explosive hydrogen bubble.