Note#96

Types of fluid service according to B31.3
(a) Category D Fluid Service: a fluid service in which all the following apply:
(1) the fluid handled is nonflammable, nontoxic, and not damaging to human tissues as defined in para.300.2;
(2) the design gage pressure does not exceed 1035 kPA (150 psi);
(3) the design temperature is from −29°C (−20°F) through 186°C (366°F).
(b) Category M Fluid Service: a fluid service in which the potential for personnel exposure is judged to be significant and in which a single exposure to a
very small quantity of a toxic fluid, caused by leakage, can produce serious irreversible harm to persons on breathing or bodily contact, even when prompt restorative
measures are taken
(c) High Pressure Fluid Service: a fluid service for which the owner specifies the use of Chapter IX for piping design and construction; see also para. K300
(d) Normal Fluid Service: a fluid service pertaining to most piping covered by this Code, i.e., not subject to the rules for Category D, Category M, or High
Pressure Fluid Service