Category 2 equipment must prevent ignition sources even with frequent disturbances or operating faults normally taken into account, must not exceed stated surface temperatures even in abnormal situations the manufacturer anticipates, and may be opened at ignition-capable parts only when non-active or through interlocks, with a warning label otherwise; for dust the category 1 surface temperature and dust-entry rules apply. Category 3 equipment must prevent foreseeable ignition sources in normal operation and keep within stated maximum surface temperatures under intended conditions (higher temperatures in exceptional cases only with special additional measures); for dust it must not ignite mixtures from ignition sources likely in normal operation, and, including cable entries and connecting pieces, must be built so dust cannot form explosive mixtures or dangerous accumulations inside.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.