KNOW YOUR ATMOSPHERE
In certain environments, the presence of flammable gases, vapours, aerosols or dusts can lead to the formation of explosive atmospheres. If ignited, the effects can be devastating to both workers and equipment. MARECHAL® and TECHNOR® appliances are carefully designed to provide the highest levels of safety, reliability and longevity in the harshest environments.
Explosive or potentially explosive atmospheres?
What is an explosive atmosphere?
An explosive atmosphere is the result of a mixture of air with a flammable substance (liquid, gas, vapour or dust) in which, after ignition, combustion spreads throughout the mixture.
An explosive atmosphere (ATEX) is an atmosphere liable to become explosive as a result of unforeseen local and/or operational circumstances.
An explosion can occur when the three elements of the ‘Explosive Triangle’ – combustible, ignition source and oxygen – are present, under optimum conditions and in adequate quantities.
Explosion ‘Triangle’: The Three Elements
1. Combustible: A flammable substance (liquid, gas, vapour or dust).
2. Source of ignition: High temperature, electric arc, static electricity, open flame, etc.
3. Oxygen (Air): One of the elements needed to support combustion.
Explosion ‘Triangle’:
The Three Elements
Combustible
Source of ignition
Oxygen (Air)
To avoid explosions, one of these three factors must be eliminated as completely as possible. Our electrical equipment is designed: To prevent the generation of sufficient energy to cause ignition, sparking or excessive temperature; or To prevent ignition spreading to the surrounding atmosphere.
Explosion prevention: a range of Ex-certified products
Many industries, such as chemicals, oil and gas, pharmaceuticals, food and drink, energy production, mining and others, may have ATEX zones.
ATEX zones must be clearly signposted as they are areas where there is a high risk of explosion due to the presence of flammable substances.
IDENTIFYING ZONES
The European ATEX Directive defines 6 zones according to the frequency and duration of the presence of flammable substances (1). It is essential to identify these zones correctly to ensure safety and compliance in potentially explosive environments. (1) It refers to standard EN 1127-1, which states that “an explosion is a sudden oxidation or decomposition reaction involving an increase in temperature or pressure, or both at the same time”.
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AVOIDING AN EXPLOSION
Equipment intended to operate in potentially hazardous atmospheres must:
- Prevent the formation of an arc which could ignite the surrounding atmosphere or contain the ignition
- Resist shocks, with higher requirements than those imposed on conventional industrial equipment
- Not be able to accumulate electrostatic charges that could generate a spark
- Have a maximum temperature below the auto-ignition of the surrounding atmosphere
When designing equipment, it is necessary to consider the type(s) of protection appropriate for equipment intended to be installed in potentially explosive atmospheres by taking one of the following actions:
- Removal of the explosive atmosphere
- Removal of the ignition source
- Ensure non-propagation of the ignition
PROTECTION SYSTEMS
Focus on the main types of protection
Explosion-proof enclosure: Ex da, db or dc
Explosion-proof equipment is an enclosure in which equipment/components that can ignite an explosive gas atmosphere are contained. An explosion-proof enclosure must:
- Constrain an internal explosion without deformation of the enclosure (withstand explosion pressure)
- Guarantee that the ignition is not propagated to the surrounding atmosphere
- Have an external temperature below the self-ignition temperature of the atmosphere
Explosion-proof enclosure: Ex da, db or dc
Construction parameters for explosion-proof equipment, which are specific to the gas group for which the equipment is intended, are essential in order to satisfy all three criteria:
- type of flame passage: threaded, flat surface, sealed passage, cylindrical, etc.
- the flame path length (= flameproof seal)
- the space between the 2 surfaces of the flameproof seal (=interstice)
- wall thickness
Explosion-proof enclosure: Ex da, db or dc
In order to guarantee the properties of the protection mode, it is necessary to:
- check that all screws closing the covers and cable entries are tight
- check that the locking device, if fitted, is tight
- never tamper with the product
Increased safety: Ex eb or ec
Increased safety equipment must, by design and with a high degree of safety, provide for the possibility of excessive temperatures and the occurrence of arcs or sparks, in normal service or under specified abnormal conditions.
Unlike an explosion-proof enclosure, all equipment or components installed in the increased safety enclosure must first be ATEX/IECEx certified for the relevant use (or assessed with the enclosure) and must also be listed in the certificate.
Increased safety: Ex eb or ec
These enclosures must have a minimum IP54 rating.
The electrical parameters are defined by the temperature rise and the distances in air and leakage lines, the latter being different from those defined in other industrial standards.
Connection quality is essential for the protection of increased safety equipment.
MARECHAL® plug socket-outlets are fitted with elastic connection terminals with conductor protection tabs to prevent damage to the conductors and ensure even pressure on all the wires (to control overheating).
To ease installation and maintenance, TECHNOR® appliances are fitted with pre-certified connection elements.
Encapsulation Ex ma, mb or mc
Parts of equipment which can ignite an explosive atmosphere by sparking or heating are enclosed in a compound so that ignition of a layer of dust or an explosive atmosphere cannot occur under operating or installation conditions.
The compound prevents the formation of an explosive atmosphere in the vicinity of dangerous components and can be considered, in some cases, as the enclosure of the appliance. For this reason, the choice and quality of the compound’s properties are essential to guarantee product safety.
This type of protection is suitable for gaseous and/or dusty applications.
TECHNOR® LED modules designed for installation in enhanced safety enclosures are protected by a transparent compound (allowing the luminous flux to pass through).
Intrinsic safety: Ex ia, ib or ic
An intrinsically safe appliance and its interconnection wires exposed to the potentially explosive atmosphere are intrinsically limited in energy, preventing ignition of the surrounding atmosphere by spark or thermal effect.
This mode of protection is suitable for gaseous and/or dusty applications.
The components of these intrinsic safety circuits must be easy to identify on an installation:
- via the light blue colour of these interconnection wires and elements
- or via complete identification of the circuit with labels
However, it is compulsory to have protection (e.g. intrinsic safety barrier) upstream of the appliance – this protection is either installed in a non-hazardous area or in an explosion-proof enclosure, if the latter allows it. Low-power circuits, electronic instrumentation, control or measurement processes are mainly protected by intrinsic safety.
Intrinsically safe appliances are often mixed with non-energy-limited devices in flameproof or increased-safety enclosures from TECHNOR®. This is possible by complying with installation rules.
Protection by Ex ta, tb or tc enclosure
Equipment that is protected against the ingress of explosive dusts has a degree of protection of IP5X or IP6X, depending on the type of dust in its atmosphere. The surface temperature of this equipment must also be controlled.
All MARECHAL® and TECHNOR® equipment can be installed in explosive dust atmospheres with an IP6X or IP5X degree of protection.
Pressurization Ex pxb, pyb or pzc
A protective gas is maintained in these enclosures at a pressure higher than that of the surrounding external atmosphere by means of a pressurisation system, so that this atmosphere does not penetrate these enclosures.
With alarms built into the system, the equipment installed does not always have to be certified.
This is an alternative to an explosion-proof enclosure where the enclosure dimensions are large but parallel control is required. TECHNOR® QPREX enclosures are protected by this mode of protection.
Possible combinations: Ex db eb/db eb mb To design safe equipment that can be installed in a potentially explosive atmosphere, it is essential to apply the most appropriate type of protection. MARECHAL® and TECHNOR® appliances combine several protection systems.
Example of an ATEX and IECEx
certified DECONTACTOR™
II 2 G D Ex db eb IIC T6 or T5 Gb
Ex tb IIIC T70 °C or T90 °C Db
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Ex eb and Ex tb enclosure
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Ex eb connection terminals
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Ex eb connection terminals
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Ex db enclosure
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Ex eb and Ex tb enclosure
MARECHAL® AND TECHNOR®
PRODUCT CERTIFICATIONS
In some countries and markets, specific certification is required. MARECHAL® and TECHNOR® appliances are certified for some of them.
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Europe
EUROPEAN DIRECTIVE (ATEX)
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Brazil
INMETRO (Portaria 179)
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South Korea
KCs (Korean Ex Certification)
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South Africa
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Eurasia (Russia – Belarus – Kazakhstan – Kyrgyzstan – Tajikistan)
EAC Ex (TR CU)
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Japan
Ordinance on Examination of Machines
and Other Equipment of the Ministry of Health,
Labour and Welfare. -
North America
UL for USA
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North America
CSA for one application
Canada and USA -
United Arab Emirates
ECAS-Ex
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India
PESO
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Australia
IECEx is recognised
as local certification
MARECHAL® and TECHNOR® appliances have all the necessary international and local certifications. These certifications guarantee that our equipment is fully compliant, ensuring the safety of people and property as well as high performance in potentially explosive environments.
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