Intrinsic safety categories

Firedamp-proof apparatus, type of protection intrinsic safety, according to IEC 60079-11 and/or EN 50020, are not subjected to any classification with respect to MIC or MIC/MIC (CH4) ratio it is MIC/MIC (CH4) =1 in this case. Intrinsic safety covers two categories of intrinsically safe circuits ... 

In the United States the discrimination between categories ia and ib is necessary only if the IEC-based classification of hazardous areas has been adopted. According to the differentiation into Divisions 1 and 2 (still predominant), one single type of intrinsic safety (IS) has been defined, requiring a two-fault assessment. 

Items in seismic category 2 should follow the practice for design, installation and maintenance for nuclear applications. However, in the hypothesis in para. 2.18 (b) (interacting items), lower intrinsic safety margins than those specified in nuclear standards can be applied when the probability of interaction with items in seismic category 1 or 3 is considered very low. 

Since integrity is required for EE-C2 items and only limited (or, in some cases, no) functionality is required to prevent their interaction with Category 1 items, more simplified and less conservative criteria for design, installation and maintenance may be used, in some cases with a lower intrinsic safety margin than for EE-Cl items, in relation to their probability of being the initiator of an... 

Hence, it becomes possible to prevent electronic instrumentation from becoming a source of ignition in the plant areas if its temperature and stored energy levels can be limited by design, to values below the thresholds for the categories of gases on the plant. We know this from of protection as INTRINSIC SAFETY. This is a form of hazard prevention. It must not be confused with a safety instrumented system but it does feature in the list of risk reduction measures. 

Power supply for intrinsically safe circuits, category ia, for mining application, flameproof enclosure, terminal box in increased safety on the line power side ... 

Some tasks do not provide intrinsic or natural feedback. In this case, it is necessary to add an extrinsic, or extra, consequence to support or redirect the behavior. Many, if not most, safety behaviors fall in this category. 

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