Electrical equipment for flammable gases and dust uses specialized designs like explosion-proof (Ex d), intrinsically safe (IS), increased safety (Ex e), or dust-ignition proof (Ex t) enclosures and circuits to prevent sparks, heat, or internal explosions from igniting hazardous atmospheres, relying on containment, energy limitation, temperature control, or purging to meet standards like UL 1203 and NEC and ensure safety in Class I (gas), II (dust), and III (fiber) locations. Symbol Type of protection Basic concept of protection e Increased safety No arcs, sparks or hot surfaces, enclosure IP54 or better n Type ‘n’ (non-sparking) Type ‘n’ (closed-break) Containment of the explosion Type ‘n’ (sealed and hermetically sealed) Keep the flammable substances out Type ‘n’ (restriced breathing) d Flameproof Containment of the explosion q Powder filled Quenching of the flame ia Intrinsic safety Limitation of spark energy and surface temperatures ib ic px Pressurised enclosure Keep the flammable substances out py pz ma Encapsulation mb mc o Oil immersion Op pr Optical radiation Inherently safe, protected by shutdown Op sh Op is ta Dust ignition protection by enclosure Dust-tight enclosure tb tc pd Pressurised enclosure Keep the flammable substances out
