Fire class is a term used to denote the type of fire in relation to the combustion material which have ignited, a Class D Fire is described as combustible materials consisting of Magnesium, Sodium, Titanium, Potassium etc.
Class D fire rating explained.
Using a European fire testing centre guidelines for the test, the test apparatus consists of a 50cm by 50cm tray and 10cm in height. Magnesium turnings are loosely and evenly filled in the tray with a hollow cylinder shaped in the turnings. 2 litres of heptane are added to one corner of the tray. The turnings will be ignited in the tray and allowed to burn for 20 minutes.
The fire fighter is then allowed to extinguish the fire at their discretion either in one hit or in short successive bursts.
To be deemed successful there shall be no visible flames after extinguishing and the test is allowed to continue. The fire observed for a further 20 minutes and then the fire is delicately observed in the heart of the fire.
If only a few independent hot spots are visible that do not exceed 10% of the surface and is not propagating the test has passed.
CLASS D RATINGS
Available sizes that have been tested to extinguish a Magnesium fire:
Fire test guidelines are designed to be several times the magnitude of anything the extinguisher would be expected to tackle in the real world.