Explosion protection

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Warning of an area in which explosive atmospheres can occur according to Directive 1999/92 / EC
Explosion protection mark for devices and protective systems for use in potentially explosive areas, according to Directive 2014/34 / EU

The explosion protection is a branch of engineering that deals with the protection against the development of explosions employed and their effects. It belongs to the field of safety technology and serves to prevent damage to people or property. These can have their cause in human error (incorrect assessment of existing working conditions) or defective work equipment, which are effective ignition sources of the system to be assessed. Explosion protection is achieved by implementing "integrated explosion safety" through primary, secondary and tertiary protection goals. First of all, they include avoidance strategies which, for example, have to avoid the formation of explosive mixtures through substitution, to the extent that this is possible according to the legally defined state of the art. Only if this cannot be implemented do secondary technical and possibly also organizational measures take effect, which have the general protection goal of absolutely avoiding the ignition of explosive mixtures that occur. Only when this cannot be reliably prevented technologically does the tertiary protection goal of limiting the effects of explosion protection take effect (e.g. pressure-resistant construction, outdoor exhibition with protective and possibly also safety distances).

This is based on statutory provisions such as EU law on hazardous substances, the directive on the use of work equipment, the ATEX directives of the European Union or the National Electrical Code (NEC) in the USA.

In Germany, the law on hazardous substances (Ordinance on Hazardous Substances with the Technical Rules TRGS) and the Industrial Safety Ordinance with the Technical Rules (TRBS) take priority.


Marking an area with explosion hazards in a chemical plant

The necessity and importance of the regulations of explosion protection has grown with the ongoing progress in industrialization. Explosion hazards must be considered not only in the chemical industry and mining , but also in many areas of the processing industry. In addition to the well-known classic areas such as mills, warehouses for grain, etc. there are other production areas, for example in the textile industry or the woodworking industry, in which the increased processing speeds and increased mechanization lead to greater abrasion of the materials involved and thus to increased wear Hazard potential comes. Due to the tendency towards ever larger production units, higher production volumes and not least because of the more restrictive legal provisions, the number of potentially affected companies has increased.

Under certain conditions, explosions can occur in technical systems, killing people and causing major property damage. One example is firedamp explosions in mining. The ignition of mine gas is often followed by even more violent explosions due to the ignition of coal dust. The worst explosion in Germany occurred in 1921 at BASF's main plant in Ludwigshafen-Oppau , killing 561 people. In 1979 a severe flour dust explosion occurred in the Roland mill in Bremen , which resulted in 17 deaths. In 2001 there was an explosion of 300 tons of ammonium nitrate in Toulouse . 31 people died here and large areas around the factory were devastated. The effects of explosions pose a significant hazard.


When dealing with substances that can react with air or oxygen , there is always a risk of explosion to be expected if the combustible substance is present in a room with a certain partial pressure or as fine-grain dust in the air. An explosive gas-air mixture is present when the proportion of the combustible gas or a vaporized liquid lies between the lower (LEL) and upper (UEG) explosion limit . In the case of dusts, the size of the dust grains and a minimum density must be sufficiently small for an explosive atmosphere to occur. There is also a lower explosion limit for dust, which is determined experimentally.

Safety-related parameters

Explosion triangle of the gas mixture methane / air [oxygen content] / inert gas (nitrogen or CO 2 )

An explosion is “a sudden oxidation or disintegration reaction with an increase in temperature, pressure or both at the same time” ( ISO 8421-1, EN 1127-1 ). An explosion is only possible in a certain mixing ratio range between flammable substances (gas, dust) and air. In the case of dust explosions , the grain size is still an important parameter. The smaller the grains, the larger the surface and thus the faster the reaction .

The term "safety-related parameters" is used to determine values ​​for substances that are necessary when determining explosion protection measures. These values ​​are usually chemical-physical values ​​that are made available in databases (e.g. CHEMSAFE , GESTIS or GESTIS dust databases) in order to make concrete statements about e.g. B. ignition sources or system strengths. These values ​​are very often missing (especially in the case of dusts) and must therefore be determined experimentally.

Important safety-related parameters include:

  • Explosion limits - mixing ratios between combustible substance and oxidizer (typically air)
  • Minimum Ignition Energy - The energy required to ignite the ignitable mixture of substance in a particular oxidizer.
  • Minimum Ignition Pressure - The minimum total pressure required to ignite the ignitable mixture of the substance in a given oxidizer.
  • Limit gap width (MESG) - The limit gap width for a specific gas mixture is determined in a standardized procedure (IEC 60079-1). It is determined which maximum width, i.e. width, a 25 mm long gap (in a container of the gas) still prevents ignition. (EN 60079-20-1)
  • Explosion points
  • Flash point

In an explosion triangle, different areas can be shown for an explosive gas-air-inert gas mixture (specification of the oxygen content).

  • Below line BC: area below the lower explosion limit; the propagation of an explosion is not possible,
  • Triangle ABC: explosive mixture,
  • Above section AC: area above the upper explosion limit; the propagation of an explosion is not possible,
  • Area to the right of point C: Due to the inertization of the mixture, explosion propagation is not possible.

The maximum explosion pressure is achieved with a stoichiometric ratio of combustible gas and air. The maximum explosion pressures of hydrocarbons and air are between 8 and 10 bar. The more the composition of a combustible gas and air mixture deviates from the stoichiometric ratio or a gas not involved in the reaction ( inert gas ) is mixed in, the lower the temperature and pressure increase in the event of ignition. If the temperature is no longer high enough for radicals to form for the reaction, then an explosion can no longer propagate.


Combustible dusts can be ignited if the dust has a small particle size (usually less than 0.5 mm particle size). In addition to an effective ignition source, a prerequisite for an explosion is a sufficient density distribution of the dust in the atmosphere. The lower explosion limit used here is given based on the dust density in the air (in g / m³). A dust deposit of less than a millimeter in a room can already result in a dangerous, explosive atmosphere if whirled up. The density distribution of the dust in the atmosphere varies greatly over time. Therefore, in contrast to the approaches for gaseous explosive substances (determination of the concentration of gases in the air via the temperature-dependent partial pressure ), no clear statement can be made regarding the reaching of the explosion limits. If dusty substances have a sufficiently fine grain size and are present in sufficient concentration in the atmosphere, there is a risk of a dust explosion and explosion protection measures must be taken.

Criteria for the effect of a dust explosion are

  • Median value of the grain size distribution,
  • lower explosion limit ,
  • Maximum pressure build-up over time per cubic meter of volume: K St in bar m / s,
  • maximum explosion overpressure,
  • the minimum ignition energy.

The dust explosion classes are divided according to the K St values. The sources of ignition are dusts

Glow nests

There is a risk of self-ignition, especially when combustible dusts remain there for a long time. As long as combustible dust ignites in a non-moving bed, the combustion proceeds slowly after self-ignition, since little air can flow to the smoldering nest. However, if the dust with the glowing nest is carried out by a conveyor system with a high proportion of air, the glowing nest acts as an ignition source for the dust-air mixture to be considered. Since smoldering spots cannot be ruled out in many technical applications, suitable measures must be taken in this case to avoid the risk of explosions.

  • Detection of glowing nests through the monitoring of surface temperatures or better through an automatic CO measurement,
  • Initiation of countermeasures after the detection of glow nests (inerting with CO 2 , N 2 or water vapor),
  • Explosion pressure shock resistant construction or installation of pressure relief flaps and design of the component according to the reduced explosion pressure according to VDI 2263 and VDI 3673 (pressure relief of dust explosions) or DIN EN 14491 (systems for pressure relief of dust explosions).
  • Local limitation of explosions by installing quick-action fittings, extinguishing agent barriers or lock systems. Explosion-related decoupling can also be achieved using a suitable rotary valve certified as a protective system .

Therefore, the measure of avoiding ignition sources when considering dusts is often not a sufficient explosion protection measure.

Ignition on hot surfaces

The ignition of dust on hot surfaces must also be considered in particular. Organic dusts in particular have poor thermal conductivity . A heat-insulating layer of dust on electrical equipment leads to an increase in the surface temperature. If the dust deposit is sufficiently thick, the smoldering temperature can be reached and cause ignition. Compared to gases and vapors, dusts have a significantly higher ignition energy . However, it must be taken into account that dust can become highly charged, for example when conveying pneumatically.

Consideration of ignition sources

An evaluation of the ignition sources in the case of dust explosions has shown that mechanical sparks / mechanical heating is the main ignition source (32.7%); this is followed by glowing nests (12.7%) and electrostatic discharges (8.5%).

Database of combustion and explosion parameters of dusts

The GESTIS-STAUB-EX database includes important combustion and explosion parameters from currently over 7000 dust samples. from many different industries as a basis for the safe handling of flammable dusts and for planning protective measures against dust explosions. The data collection is created and maintained by the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA)

The data comes from the following test centers: Federal Institute for Materials Research and Testing (BAM), Trade Association for Food and Hospitality (BGN), Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA), DMT-Gesellschaft für Forschungs undprüfung mbH , Department for Fire and Surface explosion protection - Mining test track (BVS), Henkel KGaA .

The database may be used publicly. Commercial use or partial or complete transfer to other information systems is not permitted without the express approval of the DGUV . Any liability is excluded.

Measures for explosion protection

Methodical approach

Methodical approach to explosion protection

The explosion protection measures are divided as follows:

Primary explosion protection
Measures which prevent or limit the formation of dangerous explosive atmospheres (avoiding explosive atmospheres).
Secondary explosion protection
Measures which prevent the ignition of dangerous explosive atmospheres (avoidance of effective ignition sources).
Tertiary explosion protection
Measures that limit the effects of an explosion to a harmless level (constructive explosion protection).

The explosion protection measures listed above must be given priority over those below. If it is determined within the scope of the explosion protection document that one measure is not sufficient, the measures can also be combined.

Primary explosion protection

The priority is to avoid an explosive atmosphere. Explosion protection must be brought about as planned. In Germany, the hazards must be determined in accordance with the Industrial Safety Ordinance (BetrSichV) . In addition, the Ordinance on Hazardous Substances (GefStoffV) and the Explosion Protection Ordinance (11th ProdSV) must be applied.


In order to avoid or minimize the risk of an explosion, it should first be checked (see hierarchy of measures ) whether the potentially explosive substance can be replaced by other substances that do not pose a risk of explosion (e.g. replacement of solvent-based paints with water-soluble ones) or the likelihood of an explosion is reduced (e.g. replacement of pure aluminum powder with aluminum powder that is suspended in oil and is therefore no longer accessible to the air).

Removal and dilution of the explosive substances

In the case of explosive dusts, the risk of explosion can be eliminated by removing them regularly, preferably by washing them off. It must be ensured that the cleaning devices used must not cause an explosion themselves during operation. This risk exists, for example, with non-explosion-proof vacuum cleaners. If, for example, shooting ranges are cleaned with non-explosion-proof vacuum cleaners, there is a high probability of a serious explosion, since undetonated fine gunpowder collects in the vacuum cleaner and can be easily ignited. Even at first sight harmless substances such as flour or wood dust can unexpectedly explode during cleaning. Electrostatic charge can then also be used as an ignition source . In the case of explosive vapors from liquids or gases, an explosive atmosphere can be achieved by preventing accumulation through removal combined with dilution well below the lower explosion limit (LEL). This is equivalent to removing and diluting explosive dusts.

Passivation of explosive substances

The conditioning can transform the explosive substances into a non-explosive state. It is important to ensure that the conditioning remains effective for a sufficiently long time. A tried and tested method is, for example, the treatment of dusts that are explosive when dry with hygroscopic substances that bind moisture from the air and thereby keep the substance permanently so moist that it cannot be whirled up into an explosive mixture.

For example, spraying the dusty areas with concentrated hygroscopic magnesium chloride solution (MgCl 2 (aq.)) Has proven itself . This is a widespread method in mining for moistening coal dust, which is deposited on horizontal or inclined surfaces of the route extension or other angles and can thus be prevented from being whirled up in the event of a firedamp explosion. The disadvantage is that magnesium chloride solution has a highly corrosive effect.


By inerting, for example with nitrogen, a gas cushion can be applied over a flammable, flammable liquid, thus avoiding the formation of an explosive atmosphere (avoidance of the explosion triangle: “covering”).


The explosive substances should be stored technically tight or processed while avoiding the addition of air.

Secondary explosion protection

This means avoiding effective ignition sources. The areas in which a dangerous explosive atmosphere (g. E. A.) can occur must be designated as potentially explosive zones. In order to prevent an explosion in these zones, no effective sources of ignition may be used. As ignition sources need to vary according to the circumstances

be taken into account.

The higher and longer the probability of a g. e. A., the higher the demands on the devices used there. The extent of a potentially explosive zone depends on the amount of the substance under consideration and the primary explosion protection measures taken (e.g. ventilation, gas warning system ). Furthermore, the specific properties of the substance must be taken into account when defining the zone (density in relation to air, explosion limits, maximum explosion pressure, rate of pressure build-up).

The spatial extent of a potentially explosive zone can be reduced by ventilation measures or an Ex zone with lower requirements can be selected. For example, if a limit value is exceeded on a gas warning system, there is the option of switching on forced ventilation or switching off non-explosion-protected equipment. The protective measures are usually initiated at 25% to 50% of the lower explosion limit (LEL).

Constructive explosion protection

It is not always possible to reduce the risk of an explosion to the required level by selecting suitable equipment. Additional explosion protection measures must then be applied in order to control and limit the effects of an explosion in order to exclude any risk to persons. The tertiary explosion protection is used when the measures of the primary and secondary explosion protection are insufficient.

  • Compressors for explosive gas mixtures which cannot be excluded as an ignition source,
  • pneumatic conveying of explosive dusts,
  • Silos and bunkers for explosive dusts in which the formation or introduction of glowing nests is possible,
  • additional measure in zones 0 and 20.

The following measures are possible

  • explosion pressure or explosion pressure shock resistant construction of apparatus and structures that withstand the explosion pressure ( structural explosion protection ),
  • Flame arresters that cool a flame front to such an extent that an explosion remains spatially limited,
  • Water immersion in pipelines, which also interrupt an explosion ( flame arrester ),
  • automatic quick-closing devices in connection with suitable IR detectors, which close valves in connected pipelines with a sufficiently short reaction time,
  • independently operating closure valves in pipelines for gas ( "Ventex valves"), which close off line sections with a sudden pressure increase.
  • Explosion suppression systems (e.g. automatic foam extinguishing devices) triggered by suitable IR detectors or pressure sensors with evaluation devices. With these systems, an explosive reaction is recognized and suppressed (extinguished) before greater damage occurs due to an inadmissible increase in pressure. The use is mostly combined with other explosion protection measures, for example quick-closing devices, dynamic flame arresters in order to spatially limit the explosion.
  • Pressure relief devices (pressure relief flaps, bursting discs ) that limit the explosion pressure to a manageable level (for example on large silos ). Safety valves are not suitable for dissipating the increase in pressure through an explosion, since this requires large relief areas.

Classification of the potentially explosive zones

Potentially explosive areas are divided into zones according to the frequency and duration of the occurrence of a dangerous, potentially explosive atmosphere.

Classification of the potentially explosive zones
Gases Zone 0 Zone 1 Zone 2
(Definition according to BetrSichV and GefStoffV) ... is an area in which a dangerous, explosive atmosphere as a mixture of air and flammable gases, vapors or mists is present continuously, over long periods of time or frequently.

Application interpretation: The term "frequently" is to be used in the sense of "predominantly over time", which means that potentially explosive areas are to be assigned to Zone 0 if more than 50% of the explosive atmosphere prevails during the operating time of a system. This is actually only the case inside pipes and containers.

(Definition according to BetrSichV and GefStoffV) ... is an area in which, during normal operation, a dangerous explosive atmosphere can occasionally form as a mixture of air and flammable gases, vapors or mists.

Application interpretation: If the presence of an explosive atmosphere exceeds a period of about 30 minutes per year or if this occurs occasionally, for example daily, but is less than 50% of the operating time of the system, it is generally believed that Zone 1 is present.

(Definition according to BetrSichV and GefStoffV) ... is an area in which a dangerous, explosive atmosphere as a mixture of air and flammable gases, vapors or mists normally does not occur during normal operation, and if it does, then only rarely and for a short time.

Application interpretation: There is a general consensus among many experts that the term “short-term” corresponds to a period of around 30 minutes per year. It is also stated that an explosive atmosphere is normally not to be expected during normal operation. If an explosive atmosphere occurs briefly once a year, the affected area should be classified in zone 2.

Dusts Zone 20 Zone 21 Zone 22
is an area in which a dangerous, explosive atmosphere in the form of a cloud of combustible dust contained in the air is present continuously, for long periods or frequently. is an area in which a dangerous, explosive atmosphere in the form of a cloud of combustible dust contained in the air can occasionally form during normal operation. is an area in which, during normal operation, a dangerous, potentially explosive atmosphere in the form of a cloud of combustible dust contained in the air does not normally occur or only occurs for a short time.

In Germany, before the introduction of the ATEX directives and the EN standards, dust was divided into Zone 10 (today corresponds approximately to Zone 20/21) and Zone 11 (today approximately corresponds to Zone 22).

In the zones, the likelihood of the effectiveness of ignition sources must be reduced. In zone 2/22, it is sufficient if the devices do not have any operational ignition sources. For devices with ignition hazards that are used in Zone 1 or 21, the effectiveness of the avoidance of ignition sources must not be impaired even if a fault occurs. In zone 0/20, very rare faults that represent an ignition source must be eliminated when designing the devices.

For the classification of zones, the parameters of explosion limits, releasable amounts of substance and volume flow of the ventilation measures as well as any monitoring devices used are relevant. The amount of substance that can be released and the probability and duration of a leak is often difficult to quantify. The collection of examples in the appendix to DGUV rule 113-001 (formerly BGR 104) can serve as a guide to the expansion of potentially explosive zones.

Ex zone plan for a pulverized lignite silo

Zoning inside apparatus

Explosion zone 0 must be set inside storage containers that are open to the atmosphere and in which liquids are stored that frequently heat up above the flash point. The Ex zone can be reduced, for example, by inerting with pressure control. Zone 1 can be reached if the probability of the occurrence of an explosive mixture according to the definition for Zone 1 can be reduced by additional monitoring equipment (occasional occurrence).

Apparatus or pipelines that always contain a gas mixture above the upper explosion limit, even taking into account very rarely occurring errors, are not considered to be potentially explosive zones. This includes, for example, natural gas pipelines or liquid gas pipelines, as these are always operated with overpressure compared to the atmosphere. However, special conditions are imposed if these components are to be refilled with the combustible material after they have been emptied. Any air it may contain must be flushed out or the apparatus must be rendered inert before filling. Corresponding operating instructions are required for this (see also explosion protection document).

Zoning in rooms

Rooms with apparatus or pipelines in which there are substances that can form an explosive mixture with the air do not have to be regarded as potentially explosive zones if the components are permanently technically tight. A technically tight static connection includes welded designs, flange connections with tongue and groove or flat sealing surfaces if metal-reinforced or metal-encased seals are used.

The precise definition of a "technically tight connection" is contained in TRBS 2152 Part 2 Section

Another potential outlet point for explosive gases can be dynamically loaded seals such as shaft bushings. With simple shaft seals, a potentially explosive zone must be identified. A technically tight design is achieved with magnetically coupled pumps or shaft bushings with a double-acting mechanical seal. A technical tightness can be achieved on spindle leadthroughs of fittings by sealing with bellows and safety stuffing box or stuffing box sealing with automatically adjusting packings.

A "permanent" technical tightness of a connection presupposes that minor leaks are detected early. Therefore, infrastructural measures must ensure that suitable leak tests are carried out in specified periods. If technical tightness is selected as an explosion protection measure in the long term, then, in addition to the material requirements, a regular tightness test must also be carried out.

In the following cases, an explosion zone classification is necessary when handling explosive substances: opening of apparatus, decanting, spraying or sampling. Information from the employers' liability insurance association (BGI) can be helpful for defining zones. An area of ​​Zone 2 usually follows an area of ​​Zone 1. If the entire room is assigned to zone 1, the door area to an adjacent room may have to be classified as zone 2.

Classification of the devices that can be used in potentially explosive zones


Devices that can be used in a potentially explosive atmosphere are divided into three groups. Until the introduction of EN 60079-0: 2009 for explosion-protected electrical equipment, only two groups were divided.

Device group I
stands for devices that are used in underground operations in mines and their surface systems that can be endangered by mine gas and / or combustible dust. It comprises the device categories M1 and M2

Device group II

stands for devices that are used in other areas that can be endangered by an explosive atmosphere. It includes device categories 1, 2 and 3: Devices that are to be used in this device group must be appropriately marked according to their suitability
By the device category
for which zone they are suitable and the attached code letters G for gases, mists and vapors and D for dusts in which area they may be used. The combination G / D is also possible for devices that can be used in gas and dust.
With explosive gases, mists and vapors
Category 1G for use in Zone 0
Category 2G for use in Zone 1
Category 3G for use in Zone 2
With explosive dusts
Category 1D for use in Zone 20
Category 2D for use in Zone 21
Category 3D for use in Zone 22
By the explosion group
for which substances they are suitable
With gases, mists and vapors
IIA, IIB, IIC where the classification results from their specific ignitability. The substances in group IIC are the most dangerous and the substances in IIA are the least dangerous
With dust
IIIA fibers and lint, IIIB non-conductive dust, IIIC conductive dust
By the temperature class
for which ignition temperatures they are suitable. The classification T1-T6 is only possible for devices of category 1G, 2G, 3G. For devices of category 1D, 2D, 3D (dust Ex), the maximum possible temperature rise must be included in the labeling as a temperature value.
T1 maximum surface temperature> 450 ° C
T2 maximum surface temperature> 300 ° C
T3 maximum surface temperature> 200 ° C
T4 maximum surface temperature> 135 ° C
T5 maximum surface temperature> 100 ° C
T6 maximum surface temperature> 85 ° C

Device categories in Europe

The device category is derived according to the determined potentially explosive zone in which a device is to be used. The device categories are defined in the ATEX directive 2014/34 / EU or its predecessor directive 94/9 / EC, which was still applicable until the beginning of 2016. Internationally, the term "Equipment Protection Level" (EPL) is used by IEC 60079-0.

Hazardous areas except mining

According to the ATEX internal market directive 2014/34 / EU, the categories are divided from 1 to 3. The letter "G" stands for gas, "D" stands for dust. Equipment Protection Levels (EPL) are defined in IEC 60079-0 for electrical components and devices and therefore for approvals according to the IECEx scheme.

Category 1G / 1D or EPL Ga / Da devices
must be designed in such a way that they guarantee a very high level of security. Devices in this category must guarantee the required level of safety even in the event of rarely occurring faults. Even if two errors occur on the device, an ignition must not occur. They can be used in Zone 0 (Category 1G) or Zone 20 (Category 1D).
Category 2G / 2D or EPL Gb / Db devices
must be designed in such a way that they guarantee a high level of security. Devices in this category must guarantee the required level of safety and avoid ignition sources in the event of frequent or normally expected malfunctions (defects in the device). They can be used in Zone 1 (Category 2G) or Zone 21 (Category 2D).
Devices of category 3G / 3D or EPL Gc / Dc
must be designed in such a way that they guarantee a normal level of security. Devices in this category must ensure the required level of safety and avoid ignition sources in the event of foreseeable faults (defects in the device). They can be used in Zone 2 (Category 3G) or Zone 22 (Category 3D).
Hazardous areas mining

The device categories with the prefixed "M" are intended for use in mining (coal mining) ("M" = mining ). An essential feature is that the devices for this area are designed for the risk of methane gas and coal dust and take into account the special operating conditions underground. In Germany the term firedamp protection is used for explosion protection in hard coal mining.

Category M1
Category M1 devices may continue to be operated if the lower explosion limit of mine gas is exceeded. The underground lighting or measuring devices are designed according to this device group and the higher requirements for fault tolerance.
Category M2
Category M2 devices must be switched off when the officially prescribed limit value of 20 to 25% of the lower explosion limit of methane is exceeded so that the devices no longer pose a fire hazard. The safety distance to the lower explosion limit is necessary because the gas concentration is only measured at certain points, for example at those points where the mine weather leaves the coal extraction area (face). At the place where the mine gas stored in the coal is released, the concentration is generally higher; the explosion limit must not be reached there either.

Temperature classes

Temperature classes
Material examples (see also ATEX )
T1 450 ° C Carbon monoxide , methane , propane , hydrogen
T2 300 ° C Acetylene , cyclohexane , ethylene
T3 200 ° C Diesel , gasoline , hydrogen sulfide
T4 135 ° C Acetaldehyde , diethyl ether ( no other substances )
T5 100 ° C no fabrics
T6 085 ° C only carbon disulfide

Devices and equipment may only be operated in an explosive atmosphere if their maximum surface temperatures remain below the ignition temperature of the surrounding explosive mixture. For easy assessment, temperature classes have been defined into which the devices are divided according to the maximum achievable temperature. The individual substance mixtures are assigned to corresponding temperature classes (T1 to T6). When determining the temperature class of an item of equipment, the maximum permissible ambient temperature to which it is exposed must be taken into account, as this has an influence on the achievable device temperature. The respective standards stipulate which safety distance must be observed between the ignition temperature and the device temperature.

For dusts, the ignition temperature is determined for a layer (A value) and a cloud (B value). The permissible surface temperature limit is calculated from the minimum of the two values ​​(A −75 ° C) or 2/3 * B.

Types of protection

Technical measures must ensure that no ignition source can act according to the classification of an assumed explosive mixture (gap width, temperature class). There are several technical ways of achieving explosion protection for an electrical device. The types of protection are listed in the table. In the Ex marking of a device, the type of protection is indicated by the first letter of the type of protection.

Type of protection description
t Housing protection
Type of protection only for dust explosion protection. The housing is securely sealed against the ingress of dust. This requires the housing to be sealed to IEC / EN 6052 of IP6x. In addition, surfaces exposed to dust must not exceed a certain temperature.
c Design safety
(constructional safety)
Type of protection only for non-electrical devices. The devices are designed in such a way that they do not have any ignition sources during normal operation. The risk of mechanical faults occurring, which can lead to the development of ignition sources, is reduced to a very low level. See EN 13463-5.
d Flameproof
(flame proof enclosures)
The components that can trigger ignition are built into a housing that can withstand the pressure of the explosion. The openings in the housing are designed to prevent the explosion from being transmitted to the outside.
e Increased safety
(Increased safety)
The occurrence of sparks, arcs or impermissible temperatures, which could act as an ignition source, is prevented by additional measures and an increased degree of safety.
p Pressurization
(pressurized enclosure)
The housing of the devices is filled with an ignition protection gas. An overpressure is maintained so that an explosive gas mixture cannot reach the possible ignition sources located inside the housing. If necessary, there is continuous flow through the housing.
i Intrinsic
The electrical equipment is supplied via a safety barrier that limits current and voltage to such an extent that the minimum ignition energy and ignition temperature of an explosive mixture are not reached. The equipment is also divided into Ex-ia for Ex-Zone 0 or 1 and Ex-ib for Ex-Zone 1 or 2.
O Liquid immersion
(protection by liquid immersion)
The parts of the electrical equipment that can cause ignition are immersed in a protective liquid (mostly oil).
q Sand encapsulation
(protection by powder filling)
The equipment is filled with fine-grain sand. A possible arc is cooled to such an extent that ignition of an explosive mixture is impossible. The surface temperature must not exceed the limit value.
m Encapsulation
The parts of the electrical equipment that can generate ignition sources are embedded in potting compound so that an arc cannot penetrate to an explosive mixture outside the enclosure.
Ignition protection method (non-incendive, non-sparking)
In normal operation and with defined errors, the electrical equipment does not pose a risk of ignition.
b Ignition source monitoring Monitoring of potential ignition sources such as vacuum pumps etc. by sensors in order to be able to recognize impending dangerous conditions at an early stage.

For switchgear and transformers, the explosion protection measure of flameproof enclosure is often chosen. The measure of increased safety is often used for terminal boxes and squirrel-cage motors. A pressurization occurs mainly in equipment with higher power (switch cabinets, large motors). Intrinsically safe circuits are only considered for circuits with low power. This type of protection is used for measuring and control circuits as well as for the electrical connection of sensors and actuators. The safety barrier is arranged outside the potentially explosive zone. By encapsulating possible ignition sources in the form of a sand or oil filling or by using a suitable potting compound in connection with a corresponding limitation of the surface temperature, the explosion protection of electrical equipment can be ensured.

Legal framework and regulations


To implement the ATEX - guidelines can be applied to the norms Essential Health and Safety Requirements (ESHR) prove. For harmonized standards that are published in the Official Journal (OJ) of the European Commission, the presumption of conformity applies.

ATEX Internal Market Directive 2014/34 / EU - Manufacturer

The quality requirements for facilities and equipment, from which an ignition hazard can arise, have been harmonized across Europe. The requirements are listed in the ATEX Product Directive 2014/34 / EU; The previous product directive was directive 94/9 / EC. The ATEX Product Directive was or is also referred to as ATEX 100a or ATEX 95 (since Maastricht) or ATEX 114 (since the Lisbon Treaty came into force ), the number refers to the article in the respective contract on the functioning of the European Union . The guideline describes the requirements for the “basic health and safety requirements (ESHR)” as well as conformity assessment procedures for electrical and non-electrical devices and systems that can be used in potentially explosive areas.

Combined components (assemblies)

According to Section 44 of the ATEX guidelines, an assembly consists of combined components (e.g. pumps or compressors (mechanical ignition sources) in connection with protective systems such as flame arresters or gas analysis technology with an effect on a PCT protective device) which, when linked, provide explosion protection in the sense of of the ATEX directive. " This combined component (assembly) must be brought into circulation as a functional unit by a responsible person (who is then the manufacturer of the assembly)."

If the manufacturer only uses explosion protection-relevant components that have already been certified according to the ATEX directive and are used in accordance with the associated operating instructions, then the manufacturer must issue a declaration of conformity and CE and Ex marking of the assembly without involving a notified body . The manufacturer who carries out the assembly must prepare the following documentation:

  • Assessment of the ignition risk,
  • Preparation of technical documents (operating instructions, description of the intended use, specification of the technical standards applied),
  • List of components and safety data,
  • With modular systems; Specification of the permissible configuration of the explosion protection-relevant devices and components,
  • Declaration of conformity according to directive 2014/34 / EU.

If the combination of the components creates an additional risk of ignition or a partial device does not yet fully comply with the directive, then the assembly must be subjected to the entire conformity assessment procedure suitable for the category.


General note: The requirements of the ATEX directive 2014/34 / EU are to be implemented unchanged in the national law of the member states.

  • In Germany, this guideline was implemented into national law by the 11th Ordinance on the Product Safety Act for Explosion Protection Products (11th ProdSV).

ATEX minimum social standard directive 1999/92 / EG - system operator

The ATEX operating directive 1999/92 / EC (also referred to as ATEX 118a or ATEX 137 (since Maastricht) or ATEX 153 (since Lisbon) (refers to the article in the EU contracts)) describes the requirements for the operation of Systems in potentially explosive areas. In the ATEX directive 1999/92 / EC, the central element is the risk assessment. The employer is expected to assess possible hazards of the work equipment before using work equipment in an explosive atmosphere (work equipment can also be systems or protective systems) and derive necessary and suitable protective measures from this. The risk assessment may only be carried out by competent persons. Defined protective measures must be implemented and their effectiveness checked regularly. The test content, test periods and qualification of the testers are to be specified in the risk assessment. The protective measures taken must at least reflect the state of the art. Risk assessments must be checked regularly. Requirements for risk assessments can be found in Section 2 BetrSichV and in Section 6 GefStoffV.

The division of potentially explosive systems into zones is no longer mandatory, but can still be used. The explosion protection document is now part of the risk assessment according to GefStoffV (Hazardous Substances Ordinance).

Threatening minimum volume
A dangerous amount of an explosive atmosphere is in any case already 10 liters, in small rooms (up to 100 cubic meters room volume) already one ten-thousandth of the room volume. If this volume is set at the stoichiometric ratio of liquid gas and air, 1.6 grams of liquid gas are sufficient. The most ignitable mixture, however, is in almost all cases above the stoichiometric mixture.
General remark:
The requirements of the ATEX directive 1999/92 / EC are minimum requirements that must be implemented by the member states. The member states can also tighten the requirements.
  • Germany:

The operating regulations for explosion protection are laid down in the Industrial Safety Ordinance, which has been in force since January 1, 2003 , in which the ATEX operating directive 1999/92 / EC has also been implemented in national German law. Only devices in accordance with the ATEX product directive 94/9 / EG may be used in systems with potentially explosive areas. It is then a system that requires monitoring within the meaning of Section 2 No. 30 of the Product Safety Act (ProdSG).

The scope and type of operational inspections prior to initial start-up and recurring inspections as well as the requirements for the persons qualified to do so are described in the Industrial Safety Ordinance and the associated technical regulations (cf. § 14, 15, Appendix 2 Section 3 BetrSichV: 2015 ).

Conformity assessment procedure according to EC Directive 2014/34 / EU

Requirements for devices for use in potentially explosive areas
1 G / D
  • Individual examination (Module G) or
  • EC type test (module B) in connection with production quality assurance (module D) or EC type test (module B) in connection with product testing (module F)
2 G / D
  • Electrical equipment or combustion engines:
    • EC type test (module B) in connection with conformity with the type (module C1) or EC type test (module B) in connection with product quality assurance (module E)
    • Individual examination (module G)
  • Other non-electrical equipment
    • Internal production control (module A) and filing of the documents with a notified body
    • Individual examination (module G)
II 3 G / D
  • Internal production control
  • Individual examination (module G)

Since July 1, 2003, the EC Directive 94/9 / EC and its conformity assessment procedure must be bindingly applied to devices and protective systems intended for use in potentially explosive areas that are operated under atmospheric pressure and temperature conditions (temperature −20 ° C to 80 ° C and total pressures from 0.8 bar to 1.1 bar absolute). In the scope of application, a device is understood to mean any electrical and non-electrical equipment that represents a potential source of ignition. These include lights, control cabinets or electrical sensors that can cause ignition by sparks, arcs or hot surfaces. The guideline also includes clutches, fans, compressors or rotary feeders that can be used as an ignition source due to possible hot surfaces or damage caused by sparks from touching high-speed metal components.

The requirements for devices that are to be used in potentially explosive areas increase from Category 3 to Category 2 / M2 to Category 1 / M1. While for devices of category 3 the manufacturer can prove the conformity through internal production controls, for the other categories a notified body has to be involved and its identification number has to be indicated on the Ex-marking of the equipment. The devices can go through individual tests, or the conformity of the device with the EC directive can be demonstrated, for example, by an EC type test in connection with a tested quality assurance system (in conjunction with ISO 9000) of the manufacturer. The possible module combinations are described in Chapter 2 of the guideline (see table) and the modules are described in more detail in the annexes to the guideline.

The second group covered by the directive are protective systems. These include, for example, flame arresters that limit an explosion locally or automatic extinguishing devices. Like Category 1 / M1 devices, autonomous protective systems must be tested by a notified body.

For devices and protective systems that do not fall within the scope of the directive due to the operating conditions [temperature / pressure], the explosion protection must be verified as part of the risk assessment according to the industrial safety ordinance.


A distinction must be made between labeling according to the applied standard (e.g. IEC 60079-0, EN 60079-0) and requirements through directives (ATEX directive) or legal requirements / regulations (e.g. National Electrical Code (NEC) in USA).

Labeling according to ATEX directive 2014/34 / EU

Marking of devices for operation in potentially explosive areas according to ATEX product directive 2014/34 / EU

The ATEX directive 2014/34 / EU requires in Annex II, 1.0.5:

  • "Ex sign" ATEX logo ( epsilon kappa in a hexagon, from Greek "έκρηξη" for explosion - PHONETICAL: EKRIXI with kappa)
  • Device group ("I": mining, "II": all other areas)
  • Category as defined in ATEX directive 2014/34 / EU (1G, 2G, 3G, 1D, 2D, 3D)
  • Marking according to the applied standards
(was abbreviated to "EEx" in accordance with EN 50014 and EN 60079-0 up to 12/2004, with the adoption of the IEC standard as EN standard "Ex")
In the case of products for which production monitoring by a notified body is required, the respective number of the notified body must be indicated with the CE mark. This applies to devices or systems with an EC type-examination certificate (this is the result of the EC-type examination ) by a notified body - for electrical equipment for zones 0, 20, 1 and 21 as well as combustion engines and for mechanical equipment for zones 0 and 20th

Examples of identification numbers for 'Notified Bodies'

  • 0102 for the physical-technical federal institute; (PTB) This awards the PTB test mark .
  • 0589 for the Federal Institute for Materials Research and Testing (BAM) in Berlin

Note: BAM and PTB are jointly the higher federal authorities for explosion protection with shared responsibility.

Example of labeling according to Directive 2014/34 / EU (ATEX) and EN 60079-0: CE 0589 EX II 2G Ex e II T4

Marking according to the standard on the nameplate

EN 60079-0 (gas up to 2007 edition)
  • "Ex"
  • Type of protection, e.g. B. "ia / ib", "e", "m", "d" etc.
  • Group (I: Mining; II: Gas / Dust without Mining)
  • Letter A, B or C, if required by the type of protection (e.g. Ex i, Ex d)
  • Temperature class T1 to T6
  • "U" for Ex components (component) or "X": Additional requirements, see operating instructions
  • Permissible ambient temperature range if it deviates from −20 ° C to +40 ° C.

Example of labeling according to the standard:

Ex e II T4
Ex ia IIC T4 X
EN 61241-0 (dust)
  • "Ex"
  • Type of protection (e.g. protection by housing "tD")
  • Method of testing used, e.g. B. A21
  • IP protection level of the housing according to IEC / EN 60529
  • Surface temperature

Example of labeling according to the standard:

Ex tD A21 IP64 T120 ° C
EN 60079-0 (Edition 2009, IEC 60079-0 Edition 5) for gas and dust

This edition brings together the general requirements for gas and dust atmospheres.

  • "Ex"
  • Type of protection, e.g. B. "ia / ib / ic", "e", "ma / mb", "d" etc.
  • Group (I: mining; II: gas; III: dust)
  • Letter A, B or C for the respective gas or dust group, regardless of the type (s) of protection used
  • Temperature class T1 to T6 for gas or surface temperature for dust
  • Equipment protection level and Equipment Protection Level (EPL): "M" mining ( M ining) - "G" gas ( G as) - "D" dust ( D ust)
Ma (very high degree of danger) - Mb (high degree of danger)
Ga (Zone 0) - Gb (Zone 1) - Gc (Zone 2)
Da (Zone 20) - Db (Zone 21) - Dc (Zone 22)
  • "U" for Ex components (component) or "X": Additional requirements, see operating instructions
  • Permissible ambient temperature range if this deviates from −20 ° C to +40 ° C.

Example of labeling according to the standard (gas):

Ex e IIC T4 Gb or alternatively Ex eb IIC T4
Ex ia IIC T4 Ga or alternatively Ex ia IIC T4

Example of labeling according to the standard (dust):

Ex tb IIIC T120 ° C Db or alternatively Ex tb IIIC T120 ° C
In addition, the IP protection must also be specified, e.g. B. IP65.
Labels for gas and dust cannot be combined.

Normative documents

Harmonized standards

  • EN 1127 Explosive atmospheres - Explosion protection - Parts 1 and 2
  • EN 13237 Potentially explosive areas - Terms for devices and protective systems for use in potentially explosive areas
  • EN 14491 protective systems for pressure relief from dust explosions
  • EN 14797 Equipment for explosion pressure relief
  • EN 60079 Potentially explosive areas - parts 0-2, 5-7, 10-11, 13-15, 17-20, 25-26, 28-32, 35
  • EN ISO / IEC 80079-20-2 Explosive atmospheres - Part 20-2: Material properties - Test methods for combustible dusts
  • EN ISO / IEC 80079-34 Hazardous areas - Part 34: Application of quality management systems for the manufacture of equipment
  • EN ISO 80079-36 Explosive atmospheres - Part 36: Non-electrical devices for use in explosive atmospheres - Fundamentals and requirements
  • EN ISO 80079-37 Explosive atmospheres - Part 37: Non-electrical devices for use in explosive atmospheres - Protection through structural safety "c", ignition source monitoring "b", liquid encapsulation "k"
  • EN ISO / IEC 80079-38 Explosive atmospheres - Part 38: Equipment and components in explosive atmospheres in underground mines

National regulations

  • Industrial Safety Ordinance
  • DGUV rule 113-001 (formerly BGR 104 (before: ZH 1/10)) Rules for avoiding the dangers of an explosive atmosphere with a collection of examples (explosion protection rules - EX-RL)
  • DGUV Rule 109-001 (formerly BGR 109 (before: ZH 1/32)) Guidelines to avoid the dangers of dust fires and dust explosions when grinding, brushing and polishing aluminum and its alloys
  • TRGS 727 (formerly TRBS 2153) - Avoidance of ignition hazards due to electrostatic charges
  • BGI 740, painting rooms and facilities, structural facilities, fire and explosion protection, operation
  • VDI 2263 dust fires and dust explosions
  • VDI 3673 Bl. 1 Pressure relief from dust explosions (now EN 14491 see above)
  • TAA-GS-13 Guideline for explosive dust / air mixtures and the Hazardous Incident Ordinance, Part 2 Accident prevention and annex

See also


  • W. Bartknecht: 'Explosion protection: Basics and application', Springer, Berlin 1993, ISBN 3-540-55464-5 .
  • E. Brandes & B. Möller 'Safety parameters - Volume 1: Flammable liquids and gases'. Wirtschaftsverlag NW 2003, ISBN 3-89701-745-8 .
  • B. Dyrba: 'Practical Guide to Zoning'. Carl Heymanns Verlag, Cologne Berlin Munich 2010, ISBN 978-3-27394-9 .
  • B. Dyrba: 'Compendium Explosion Protection'. Carl Heymanns Verlag, Cologne Berlin Munich 2013, ISBN 978-3-452-25836-6 .
  • B. Dyrba: 'Lexicon of Explosion Protection'. Carl Heymanns Verlag, Cologne Berlin Munich 2009, ISBN 978-3-452-27086-3 .
  • B. Dyrba: 'Explosion protection - ATEX and important standards with practical explanations'. Carl Heymanns Verlag, Cologne Berlin Munich 2009, ISBN 978-3-452-26987-4
  • B. Dyrba: 'Explosion protection - 230 well-founded answers to frequently asked questions'. Carl Heymanns Verlag, Cologne Berlin Munich 2009, ISBN 978-3-452-26988-1 .
  • M. Kräft: 'Explosion protection with flame arresters'. 2nd edition, Mackensen, Berlin, 2007, ISBN 978-3-926535-53-5 .
  • G. Lüttgens: 'Understand - control - apply static electricity'. Expert Verlag 2010, ISBN 3-8169-2506-5 .
  • G. Lüttgens: 'Expert Practice Lexicon - Static Electricity'. Expertverlag 2013, ISBN 978-3-8169-3137-9 .
  • J. Michelis: 'Explosion protection in underground mining'. Glückauf Verlag, Essen 1998, ISBN 3-7739-0900-4
  • M. Molnare, Th. Schendler, V. Schröder 'Safety-related parameters - Volume 2: Explosion areas of gas mixtures'. Wirtschaftsverlag NW 2003, ISBN 3-89701-746-6 .
  • J. Pester: 'Explosion protection of electrical systems. Questions and answers'. Huss-Medien, Berlin 2008, ISBN 3-341-01418-7 .
  • N. Schön: 'Safety indicators for flammable gases and dusts'. Deutscher Eichverlag, ISBN 3-8064-9946-2 .

Web links

Individual evidence

  1. ^ German Social Accident Insurance eV: Hazardous substances: GESTIS substance database. Accessed June 8, 2019 (German).
  2. GESTIS - STAUB-EX. Retrieved June 8, 2019 .
  3. Employer's Liability Insurance Association for Raw Materials and Chemical Industry: Leaflet on safety-related parameters. Retrieved November 29, 2019 .
  4. Explosion-related indicators: ATEX product directive 2014/34 / EU druckgeraete-online.de, accessed February 7, 2020.
  5. : Basics of explosion protection gfd-katalog.com, Crouse-Hinds / CEAG / EATON, accessed February 7, 2020. P. 29.
  6. H. Beck: Aids for the identification of hazards when handling flammable dusts, hazardous substances - keeping the air clean 62 (2002) No. 9 .
  7. ^ Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA): Annual Report 2018. Accessed on June 6, 2019 .
  8. ^ A b Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA): GESTIS-STAUB-EX. Retrieved October 8, 2018 .
  9. EN 60079-1 Explosive atmosphere - Part 1: Equipment protection through flameproof enclosure "d".
  10. EN 60079-7 Explosive atmosphere - Part 7: Equipment protection through increased safety "e"
  11. EN 60079-2 Explosive atmosphere - Part 2: Equipment protection by pressurized enclosure "p".
  12. EN 60079-11 Explosive atmosphere - Part 11: Equipment protection by intrinsic safety "i".
  13. EN 60079-6 Explosive atmosphere - Part 6: Equipment protection by liquid encapsulation "o".
  14. EN 60079-5 Explosive atmospheres - Part 5: Equipment protection through sand encapsulation "q".
  15. EN 60079-18 Electrical equipment for areas with a risk of gas explosion - Part 18: Design, testing and marking of electrical equipment with the encapsulation type of protection "m".
  16. EN 60079-15 Electrical equipment for areas with a risk of gas explosion - Part 15: Construction, testing and marking of electrical equipment of type of protection "n".
  17. EN 60079-0: 2009 Explosive atmospheres - Part 0: Equipment - General requirements (IEC 60079-0: 2007).