The rules in Chapter VIII of ASME B31.3 are used when the owner designates a piping system to be in Category M Fluid Service. The owner is guided in the classification for the piping system by the definition of Category M Fluid Service in Chapter I of ASME B31.3. This definition is the Code rule relative to classification. A guide to the application of these rules is provided in ASME B31.3, Appendix M, which contains a flow chart to assist the owner in classifying fluid services.
The definition of Category M Fluid Service is as follows. Note that for purposes of emphasis, it has been broken into subparts, all of which must be satisfied for the service to meet the definition of Category M (ASME B31.3, para. 300.2):
“a fluid service in which the potential for personnel exposure is judged to be significant and in which a single exposure of 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.”