Explosion prevention and explosion protection according to ATEX

Determining an explosion hazard according to ATEX 137 (operator’s guidelines)


Zone division

The areas of operation must be divided into zones (VDI 2263-6/BGR 104):

Environment: Gas/mist/fumes

Hazardous if content is more than 50 % of the operation or continuous Zone 0

Occasional hazard if less than 50 % in the process Zone 1

No hazard during normal operation, or rare and short-term Zone 2

Environment: dust

Hazard if content is more than 50 % of the operation or continuous Zone 20

Occasional hazard if less than 50 % in the process Zone 21

No hazard during normal operation, or rare and short-term Zone 22

Classification into device categories according to ATEX 95 (manufacturer’s guideline)


Device group I

Includes systems for underground and surface mining.

Device group II

Classification of all systems in remaining explosion prone areas. All the following information pertains to device group 2.

Device category 1

Hazard potential: continuous, frequent or over an extended period of time
Requirement: very strict safety procedures

Device category 2

Hazard potential: occasional
Requirement: strict safety measures

Device category 3

Hazard potential: rare or short-lived
Requirement: normal safety measures

Range of applications according to product guidelines ATEX 95


In Zone 20 use only
device category 1.

In Zone 21 system in
device category 2 (+1) are permissible.

In Zone 22 suitable
device category 3 (+2 and 1).

Zone division
According to VARIO

red: Zone 20
green: Zone 22

List of process-related ignition source types according to ATEX 95


– Sparks
– Flames
– High surface temperatures
– Arcing
– dB levels
– Radiation in the visual range
– Electromagnetic waves
– Electrostatic charges
– Stray or leaking electrical currents
– Heating by friction
– Heating from impact
– Shock waves or compression
– Chemical reaction

Example: Dust extraction during aluminum processing


During the mechanical aluminum processing hot, combustible sparks and chips can be created during impact with steel components.

These ignition sources can enter the filtration zone.

Evaluation of the ignition hazard should be performed under process monitoring during the extraction of metal dusts.

Example: Dust separation during weighing, dosing, mixing in the plastic industry

A basic component of organic substances and therefore plastics (with the exception of some silicons) is carbon.

The individual characteristics of various plastics are collected inside the equipment

The flammatory behavior of plastics and the explosiveness of plastic dust is therefore variable.

Ignition sources related to the system or process themselves cannot be excluded.

Explosion prevention


To avoid hazards through explosions, explosion protection must occur systematically.

Please find information on primary and secondary explosion protection measures on pages “avoiding an explosive atmosphere” and “ignition-source free operation”.



It often makes sense to combine the possibilities of a explosion prevention with advantages of explosion protection.

A very high safety level can be reached which can tolerate malfunction sources.

Residual risk


A remaining risk due to unpredictable incidents cannot be avoided despite all measures taken.

VDI 2236, page 6 explains the performance of risk evaluations and the results of suitable protection measures.

Preventing an explosive environment



Avoiding a potential explosion seems to be an obvious safety measure – however, it may not be suitable for all processes.
(Primary explosion protection)


1. Wet separation


For this process, possible ignition sources are rinsed with water, preventing the creation of an explosive environment in the dust separator. Because of the variety of processes, this technology is not universally applicable.

Further information (Keller homepage) >



2. Inertisation


When using inertisation, the separator is supplied with inert material such as limestone powder to avoid the creation of an explosive situation.

Especially suited for this are inert gases such as nitrogen, carbon or noble gases but even powdery inert material such as limestone powder (solid matter inertisation). When using powdery inert material, the addition of nine times the amount of the explosive dust amount can be required to achieve the inertisation effect.

The mixture ratio must ensure that the combination of inert material and explosive dust/air cannot set off an explosion.

The economic feasibility depends on the volume of dust created and the need for inert material.

Ignition source free operation


An explosion can only be set off in the presence of an ignition source
(secondary explosion protection)



1. Procedural measures

These are to avoid common ignition sources such as welding, smoke and other sources of open flames.

Explosions Pentagon
Despite an explosive environment, an explosion is impossible with an ignition source-free operation



2. Eliminating ignition sources in the separation system


Inadequate for especially ignition-prone dusts with MIE < 10 mJ and hybrid mixtures.

All components inside EX zones must be approved according to ATEX in order to be ruled out as an ignition source.

If the entry of an ignition source from outside of the separation system can be prevented safely, grounding the system components is sufficient. The system is safeguarded from current leakage and stray currents.

Grounding prevents electrostatic spark discharge.

Additional conductive and grounded filter elements can be installed.



2.1 Ignition source monitoring



For processes with possible spark creation (e. g. aluminum processing), the system can be monitored by a spark sensor.

If entry is detected, the SPS can prevent the next cleaning cycle.

Additional information
(Keller homepage) >


3. Cleaning during system downtimes

If the separation process is interrupted to clean the filter elements, no ignition sources exist.

Additional information
(Keller homepage) >

Explosion protection according to BGR 104 and VDI 2263


If the above mentioned measures are inadequate to prevent an explosion and its effects, additional explosion protection methods can be installed.



Directives BGR 104 and VDI 2263 differentiate among the following protection measures:

– Explosion-proof construction
– Explosions pressure relief
– Explosions suppression
– Prevention of flame and
explosion transfer

Housing design


Explosion pressure-surge resistant

For smaller explosion hazards, the system is designed according to this category.




Explosion pressure resistant


Calculated according to the maximum explosion pressure or the reduced maximum explosion pressure, the filter housing should resist an explosion without buckling.

Explosion pressure relief for organic dusts


In outdoor installation or adjoining outer walls, it is feasible to use burst panels as an explosion pressure relief to cover a large safety zone. Please consider a possible flame outlet.

Burst panel

By integrating a flameless pressure relief, flames and heat can be adsorbed by a stainless steel mesh screen.

Please take into consideration adequate safety distances.

Dry separator VARIO with ProVent

Flameless explosion pressure relief
for metals


ProPipe Plus and TR-1 ProVent plus
ensure a danger free explosion relief in
closed rooms.

ProPipe Plus is a patented system with
flame trap and dust retention made of
stainless steel.

This system does not require a protection
zone. There exists a special design for
aluminium dusts.

ProPipe Plus at VARIO 2




TR-1 ProVentPlus is specially suited to
separate explosive dust from machine
tools with dry processes or MQL.

The combustion products of the flameless
pressure relief are guided upwards by
means of a deflection channel. A safety
zone is not required.

However, an individual assessment
according to DIN EN 16009 is required.

TR-1 ProVent Plus

Further information
(Keller Homepage) >

Explosion suppression



Suitable for reduced maximum explosion pressure
ausgelegt sind

A dynamic pressure sensor is activated when it detects the pressure in the filter area and the pressurized tank which stores the extinguishing agents.

The extinguishing agent is dispensed within 50 ms and an explosion is prevented. The emerging explosion pressure normally reaches 0.4 bar excess pressure when terminated.

The system is approved for organic dust.




Perfect for toxic dusts

Since the effects are limited only to the interior of the system, this procedure is perfectly suited for toxic dusts.




Round filter with explosion suppression

Protection against consequences of explosions and personal injury

Air pollution control systems with explosion-proof construction, explosion suppression or explosion pressure relief must be explosion-decoupled.

This is to prevent successive explosions and personal injury from the airborne shock wave and possible flames.

It must be clarified if a complete or partial flame and pressure reduction is adequate or necessary.




Decoupling the clean air duct

Normally, the advance of flames into the clean air duct is prevented by filter elements. However, filters are not considered as a protective system since they can be flammable.

The clean air duct should resist the reduced explosion pressure and may only terminate in a non-hazardous location.

As an alternative to decoupling the clean air duct, pressure relief vents
with burst panels can be installed.

Quick closing valves can also be used to decouple flame and pressure.




Dirty air duct decoupling

A verified method is our ProFlap back pressure flap.

During operation, the downstream mounted back pressure flap is kept open by the air flow. During an explosion inside a protected system, the flap is closed by the pressure surge inside the ductwork.

ProFlap back pressure flap
Additional information
(Keller Homepage) >


Extinguishing barrier (Flame barrier)

This device is activated by a sensor and dispenses depressurized extinguishing agent into the duct in the event of a dust explosion.
The flames are suffocated however the shock wave is not contained, which is the reason why the downstream system components must be designed to withstand a reduced explosion pressure.

Protection against the consequences of an explosion and personal injury


Decoupling of dust discharge

The locking function of a rotary valve can be used to avoid an explosion from spreading inside the dust collection tank. The modified design is flameproof.

The same result can be achieved with a lock.

As an alternative, pressure-surge proof design of the dust collection tank can also be selected.




Rotary valve