Factory Mutual (FM) Standard 6930, Group 01
It is regarding the flamability of the fluid
Taken from :
http://www.imakenews.com/lng/e_article000073512.cfmUnder the new standards, fluids are tested and then classified in three groups based on a complex formula called the spray flammability parameter. Group 0 fluids are nonflammable. Group 1 fluids are usually unable to stabilize a spray flame. Group 2 fluids are less flammable than mineral oils, but may stabilize a spray flame under certain conditions. Water-based fluids are generally Group 0, while phosphate esters may be Group 2.
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