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3.5.8intrinsically safe sub-circuitpart of an intrinsically safe circuit which is galvanically isolated from another part or otherparts of the same intrinsically safe circuit3.6 Intrinsic safety parameters3.6.1maximum external inductance to resistance ratioLo/Romaximum value of ratio of inductance to resistance that can be connected to the externalconnection facilities of the electrical apparatus without invalidating intrinsic safety3.7 Pressurization3.7.1pressurization “p”technique of guarding against the ingress of the external atmosphere into an enclosure bymaintaining a protective gas therein at a pressure above that of the external atmosphere3.7.2continuous dilutioncontinuous supply of a protective gas, after purging, at such a rate that the concentration of aflammable substance inside the pressurized enclosure is maintained at a value outside theexplosive limits at any potential ignition source (that is, outside the dilution area)Note 1 to entry: The dilution area is an area in the vicinity of an internal source of release where theconcentration of a flammable substance is not diluted to a safe concentration.3.7.3leakage compensationflow of protective gas sufficient to compensate for any leakage from the pressurized enclosureand its ducts3.7.4static pressurizationmaintenance of an overpressure within a pressurized enclosure without the addition ofprotective gas in the hazardous area3.8 Type of protection “n”3.8.1type of protection “n”type of protection applied to electrical equipment such that, in normal operation and in certainspecified abnormal conditions, it is not capable of igniting a surrounding explosiveatmosphere

3.8.3 associated energy-limited apparatus electrical equipment which contains both energy-limited and non-energy-limited circuits and is constructed so that the non-energy-limited circuits cannot adversely affect the energy-limited circuits 3.9 oil-immersion “o” type of protection in which the electrical equipment or parts of the electrical equipment are immersed in a protective liquid in such a way that an explosive gas atmosphere which may be above the liquid or outside the enclosure cannot be ignited 3.10 powder filling “q” type of protection in which the parts capable of igniting an explosive gas atmosphere are fixed in position and completely surrounded by filling material to prevent the ignition of an external explosive atmosphere Note 1 to entry: The type of protection may not prevent the surrounding explosive gas atmosphere from penetrating into the equipment and components and being ignited by the circuits. However, due to the small free volumes in the filling material and due to the quenching of a flame which may propagate through the paths in the filling material, an external explosion is prevented. 3.11 encapsulation “m” type of protection whereby parts that are capable of igniting an explosive atmosphere by either sparking or heating are enclosed in a compound in such a way that the explosive atmosphere cannot be ignited under operating or installation conditions