The symbol of flameproof electrical equipment consists of ().

According to Baidu Library, Ex is an explosion-proof symbol, indicating that the equipment has explosion-proof performance and can be used safely in explosive environment. D stands for flameproof and explosion-proof mode, that is, the shell of the equipment is designed to withstand the internal explosion without breaking, thus preventing the explosion from spreading to the external environment. I means that the equipment is intrinsically safe, that is, measures have been taken in the design, so even under normal working or fault conditions, sparks or high temperatures sufficient to ignite explosive mixtures will not be generated.