Safe Ignition Sources

If an atmosphere subject to explosion cannot be prevented in a work area, secondary explosion protection is brought to bear. Secondary measures include prevention of any ignition sources in the Ex area.

However, these are not so easy to detect. Only with knowledge of what can cause a spark or heat can measures be taken to prevent explosions. The ignition sources are listed in the basic standard EN 1127-1 “Atmosphere subject to explosion – Explosion protection Part 1” as well as in the “Technical rules for operational safety” TRBS 2152, Part 3. Appropriate protective measures for preventing ignition sources are also listed there.

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Ignition sources and their causes

Ignition sourceCause (example)
Hot surfacesHeating devices, mechanical processes due to friction and chipping, heat losses (friction coupling and braking)
Electric arcsMechanically generated sparks (e.g., due to friction, impact or machining processes), electrical sparks, electrical switch arcs
Flames and hot gasesFlames or their hot reaction products such as hot gases and glowing material particles can ignite an explosive atmosphere.
Sparks generated mechanicallyFriction, impact or machining processes such as grinding, tools such as wrenches, pliers or tools such as a ladder; work on rusty components with aluminum tools (thermite reaction)
Electrical systemsOpening and closing of electrical circuits, equalizing currents, electromagnetic fields, conductive dust
Note: Protective low voltage is not a measure to protect against explosion, since ignition is also possible with less than 50 V!
Cathode corrosion protectionReverse current to the current source, induction, short or ground faults
Static electricityStatic electric discharge
Lightening strike-
Electromagnetic fieldsFrequency ranges from 9 x 103 to 3 x 1011 Hz. These include high-frequency equipment such as radio equipment or high-frequency generators.
Electromagnetic radiationFrequency ranges from 3 x 1011 to 3 x 1015 Hz and wavelengths of 1000 to 0.1 μm. This includes optical radiation such as sunlight, lasers, lightning strikes, electric arcs.
Ionizing radiationIgnition due to energy absorption, with causes such as short-wave UV rays, X-rays or radioactive materials
Adiabatic compression and streaming gasesDue to the high temperatures that occur due to shock waves and in instances of adiabatic compression, an atmosphere subject to explosion can ignite.

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