Environments with Potentially Explosive Atmospheres
Moflash offer a range of Audible & Visual warning signals along with manual activation devices that have been designed for use in harsh environmental conditions and potentially explosive atmospheres, sometimes known as Hazardous Areas or Hazardous Locations.
All of these products comply with European ATEX directive 2014/34/EU and the International Electrical Commission (IEC) for Explosion atmospheres IECEx.
ATEX directive 2014/34/EU covers equipment and protective systems intended for use in potentially explosive atmospheres. The Directive defines the essential health and saftey requirements and conformity assessment procedures, to be applied before products are placed on the EU market. It is aligned with the New Legislative Framework policy, and it is applicable from 20 April 2016, replacing the previous Directive 94/9/EC. and the International Electrical Commission (IEC) for Explosion atmospheres IECEx.
Moflash ATEX & IECEx certificates have been issued by DNV NEMKO Norway. Moflash is QAN & QAR approved to manufacture these approvals on site at our Birmingham UK based factory.
These directives help classify areas where hazardous explosive atmospheres may occur into zones. The classification given to a particular zone, and its size and location, depends upon the likelihood of an explosive atmosphere occurring and its persistence if it does. Areas that have been classified into zones must be protected from effective sources of ignition. The equipment & protective systems intended to be used in zoned areas must meet the requirements of the ATEX directive.
|European and IEC Classification||Definition of Zone or Division||North American Classification|
|An area in which an explosive mixture is continuously present or present for long periods.||Class I
Division 1 (gases)
|An area in which an explosive mixture is likely to occur in normal operation.||Class I
Division 1 (gases)
|An area in which an explosive mixture is not likely to occur in normal operation and if it occurs it will exist only for a short time.||Class I
Division 2 (gases)
|An area in which an explosive mixture is continuously present or present for long periods.||Class II
Division 1 (dusts)
|An area in which an explosive mixture is likely to occur in normal operation.||Class II
Division 1 (dusts)
|An area in which an explosive mixture is not likely to occur in normal operation and if it occurs it will exist only for a short time.||Class II
Division 2 (dusts)
Explosive gases, vapours and dusts have different chemical properties that affect the likelihood and severity of an explosion. Such properties include flame temperature, minimum ignition energy, upper and lower explosive limits, and molecular weight. Empirical testing is done to determine parameters such as the maximum experimental safe gap, minimum ignition current, explosion pressure and time to peak pressure, spontaneous ignition temperature and the maximum rate of pressure rise. Every substance has a differing combination of properties but it is found that they can be ranked into similar ranges, simplifying the selection of equipment for hazardous areas.
Flammability of combustible liquids are defined by their flash-point. The flash-point is the temperature at which the material will generate sufficient quantity of vapour to form an ignitable mixture. The flash-point determines if an area needs to be classified. A material may have a relatively low auto-ignition temperature yet if its flash-point is above the ambient temperature, then the area may not need to be classified. Conversely if the same material is heated and handled above its flash-point, the area must be classified.
Each chemical gas or vapour used in industry is classified into a gas group.
|I||All Underground Coal Mining, Firedamp (methane)|
|IIA||Industrial methane, propane, petrol and the majority of industrial|
|IIB||Ethylene, coke oven gas and other industrial gases|
|IIC||Hydrogen, acetylene, carbon disulphide|
Group IIC is the most severe group. Hazards in this group can be ignited very easily indeed. Equipment marked as suitable for Group IIC is also suitable for IIB and IIA. Equipment marked as suitable for IIB is also suitable for IIA but NOT for IIC. If equipment is marked for example, Ex d IIC then it is suitable for all subgroups IIA, IIB and IIC.
|III A||Combustible Flyings|
|III B||Combustible but non-conductive Dust (The particle size of the dust grain is 500 micro meter or less, and can remain suspended in air and may settle due to its own weight)|
|III C||Combustible & conductive Dust (The particle size of the dust grain is 500 micro meter or less, and can remain suspended in air and may settle due to its own weight)|
A list must be drawn up of every chemical gas/vapour & dust that is on the refinery/chemical complex and included in the site plan of the classified areas. The above groups also indicate how much energy is required to ignite the gas by spark ignition, Group IIA requiring the most energy and IIC the least.
Effective Ignition Sources
Is a term defined in the ATEX directive as an event which, in combination with sufficient oxygen and fuel in gas, mist, vapour or dust form, can cause an explosion. Effective sources of ignition are:
- Lightning strikes
- Open flames
- Mechanically generated impact or friction sparks
- Electric sparks
- Very high surface temperatures
- Electrostatic discharge & adiabatic compression etc.
Equipment Protection Level
In recent years the Equipment Protection Level (EPL) is specified for several kinds of protection. The required protection level is linked to the intended use in the zones described below:
|Group||Ex Risk||Zone||EPL||Minimum type|
|I (mines)||de-energised in presence of Ex atmosphere||Mb|
|II (gas)||explosive atmosphere > 1000 hrs/yr||0||Ga||ia, ma|
|II (gas)||explosive atmosphere between 10 and 1000 hrs/yr||1||Gb||ib, mb, px, py, e, o, q, s|
|II (gas)||explosive atmosphere between 1 and 10 hrs/yr||2||Gc||n, ic, pz|
|III (dust)||explosive surface > 1000 hrs/yr||20||Da||ia|
|III (dust)||explosive surface between 10 and 1000 hrs/yr||21||Db||ib|
|III (dust)||explosive surface between 1 and 10 hrs/yr||22||Dc||ic|
Another important consideration is the classification of the electrical equipment. The surface temperature or any parts of the electrical equipment that may be exposed to the hazardous atmosphere should be tested that it does not exceed 80% of the auto-ignition temperature of the specific gas or vapour in the area where the equipment is intended to be used.
The temperature classification on the electrical equipment label will be one of the following (in degrees Celsius):
The above table tells us that the surface temperature of a piece of electrical equipment with a temperature classification of T3 will not rise above 200°C.
The auto-ignition temperature of a liquid, gas or vapour is the temperature at which the substance will ignite without any external heat source. The exact temperature value determined depends on the laboratory test conditions and apparatus. Such temperatures for common substances are:-
The surface of a high pressure steam pipe may be above the auto-ignition temperature of some fuel/air mixtures auto-ignition temperatures.
Auto-ignition Temperatures (dust)
The auto-ignition temperature of a dust is usually higher than that of vapours & gases. Examples for common materials are:
Type of Protection
To ensure safety in a given situation, equipment is placed into protection level categories according to manufacture method and suitability for different situations. Category 1 is the highest safety level and Category 3 the lowest. Although there are many types of protection, a few are detailed below:
|Flameproof||d||Equipment construction is such that it can withstand an internal explosion and provide relief of the external pressure via flamegap(s) such as the labyrinth created by threaded fittings or machined flanges. The escaping (hot) gases must sufficiently cool down along the escape path that by the time they reach the outside of the enclosure not to be a source of ignition of the outside, potentially ignitable surroundings.|
Equipment has flameproof gaps (max 0.006" (150 um)propane/ethylene, 0.004" (100 um)acetylene/hydrogen).
|IEC/EN 60079-1||Zone 1 if gas group & temp, class correct||Motors, lighting, junction boxes, electronics|
|Increased Safety||e||Equipment is very robust and components are made to a high quality.||IEC/EN 60079-7||Zone 2 or Zone 1||Motors, lighting, junction boxes|
|Oil Filled||o||Equipment components are completely submerged in oil.||IEC/EN 60079-6||Zone 2 or Zone 1||Switchgear|
|Sand/Powder/ Quartz Filled||q||Equipment components are completely covered with a layer of sand, powder or quartz.||IEC/EN 60079-5||Zone 2 or Zone 1||Electronics, telephones, chokes|
|Encapsulated||m||Equipment components of the equipment are usually encased in a resin type material.||IEC/EN 60079-18||Zone 1 (Ex mb) or Zone 0 (Ex ma)||Electronics (no heat)|
|Pressurised/ Purged||p||Equipment is pressurised to a positive pressure relative to the surrounding atmosphere with air or an inert gas, thus the surrounding ignitable atmosphere cannot come in contact with energised parts of the apparatus. The overpressure is monitored maintained and controlled.||IEC/EN 60079-2||Zone 1 (px or py), or Zone 2 (pz)||Analysers, motors, control boxes, computers|
|Intrinsically Safe||i||Any arcs or sparks in this equipment has insufficient energy (heat) to ignite a vapour.|
Equipment can be installed in ANY housing provided to IP54. A ‘Zener Barrier’ or ‘opto isol’ or ‘galvanic’ unit may be used to assist with certification.
A special standard for instrumentation is IEC/EN 60079-27, describing requirements for Fieldbus Intrinsically Safe Concept (FISCO) (zone 0, 1 or 2).
|'ia': Zone 0 & 'ib': Zone 1 'ic': Zone 2||Instrumentation, measurement, control|
|Non Incendive||n||Equipment is non-incendive or non-sparking.|
A special standard for instrumentation is IEC/EN 60079-27, describing requirements for Fieldbus Intrinsically Safe Concept (FISCO) (zone 2)
|Zone 2||Motors, lighting, junction boxes, electronic equipment|
|Special Protection||s||This method, being by definition special, has no specific rules. In effect it is any method which can be shown to have the required degree of safety in use. Much early equipment having Ex s protection was designed with encapsulation and this has now been incorporated into IEC 60079-18 [Ex m]. Ex s is a coding referenced in IEC 60079-0. The use of EPL and ATEX Category directly is an alternative for ‘s’ marking. The IEC standard EN 60079-33 is made public and is expected to become effective soon, so that the normal Ex certification will also be possible for Ex s.||IEC/EN 60079-33||Zone depending upon||As its certification states|
The types of protection are subdivided into several sub classes, linked to EPL: ma and mb, px, py and pz, ia, ib and ic. The a subdivisions have the most stringent safety requirements, taking into account more than one independent component faults simultaneously.
Many items of EEx rated equipment will employ more than one method of protection in different components of apparatus. These would be then labelled with each of the individual methods. For example a socket outlet labelled EEx ‘de’ might have a case made to EEx ‘e’ and switches that are made to EEx ‘d’.