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Information on explosion protection

Introduction
Forklifts that work in hazardous locations can be dangerous. The equipments’ ignition sources, like sparking components such as motors, switches and controllers, and hot surfaces from motors, brakes and engine exhaust systems, when exposed to flammable gases, vapours, liquids and combustible powders and dusts, can cause fires or explosions.
Examples of hazardous materials/gas: perfumes, cosmetics, paints, varnishes, printing ink, flour, confectionery, medicinal chemicals, botanical products, alkalies and chlorine, and synthetic rubber.
Other EX forklift users include facilities where combustible dusts are produced from handling materials like dried hay, starches and pastes, potatoes and grain, locations where there are drying rooms for evaporating flammable solvents and spray or paint booths, sewage treatment facilities that create flammable gas by-products and refrigerators that store volatile and flammable materials, etc.
 
The explosion-proof forklifts of Jiali Technology are designed for such potentially dangerous locations to ensure secure and safe material handling. They are the ideal choice for material handling in hazardous environments.
Safety and reliability are our priorities.
With the CPDY**-FB series Jiali Technology developed a series of explosion-proof hydraulic electric forklift with ASM technology from Germany. Highest safety standards, excellent design, attractive appearance and outstanding performance make us a leading company in the area of explosion-proof forklift trucks and other explosion-proof industral vehicles.
 
Design, materials and production of all Jiali industral vehicles have been designed for explosion protection from the outset. All kinds of explosion protection measures are used to reach the highest possible level of security. The forklifts electric motor, control, batteries, lighting, signal lights, etc. have either been placed in explosion-proof enclosures or have been appropriately designed to avoid sparking or dangerous temperature rise, etc.
Most forklifts and other explosion-proof industrial vehicles of Jiali belong to the explosion protection class Ex 2 G IIB T4 or Ex sde IIB T4.
2 G - unit category
II B - explosion protection class
T4 - temperature class
S - explosion-proof, special
D - explosion proof (dusts)
(for further explanation see below)
 
Explosion protection
Explosion protection measures are divided as follows:

Primary explosion protection: measures which prevent the formation of hazardous explosive atmospheres or limit it (avoiding hazardous explosive atmospheres).
 
Secondary explosion protection: measures which prevent the ignition of hazardous explosive atmospheres (avoid effective ignition sources).
 
Tertiary explosion protection: measures which limit the effects of an explosion to an acceptable level (constructive explosion protection).


The explosion protection measures above take precedence over those underneath. As far as determined in the context of the explosion protection document, if an action is not sufficient, the measures can also be combined.
 
Secondary explosion protection
The areas in which a hazardous explosive atmosphere can occur must be designated as hazardous zones. In order to prevent an explosion in these areas no effective ignition sources may be used. Depending on the circumstances the following must be considered as sources of ignition:
• Lightning,
• Electric arcs or sparks in electrical equipment (by type of protection intrinsically safe on a potentially harmless energy release of a short spark),
• Differences in potential,
• Flame,
• hot surfaces,
• mechanical shock or friction sparks,
• electrostatic charging not mono components or persons
• Floating tuft discharge non-conductive parts,
• Adiabatic compression,
• Electrostatic acceleration drops of liquid,
• short-wave radiation.
The higher and longer the probability of a hazardous explosive atmosphere is to occurr, the higher are the requirements for the equipment to be used. The extent of a hazardous zone depends on the exiting amount of the examined substance and the initiated secondary explosion protection measures (for example ventilation, gas detection system). In addition, the specific properties of the substance are to be observed (density relative to air, explosion limits, maximum explosion pressure, pressure building speed).
Ventilation measures can reduce the spatial extent of a hazardous zone or an ex-zone with reduced requirements can be selected. For example it is possible, in case of a gas detection system indicating the exceeding of a limit to enable a forced ventilation or to turn off not explosion-protected equipment or operational material. The protective measures are usually initiated at 25% to 50% of the lower explosive limit (LEL).
Already 10 litres are considered hazardous quantity of an explosive atmosphere. If this volume with the stoichiometric ratio of liquefied petroleum gas and air is applied, already 1.6 grams liquefied petroleum gas are sufficient.
 
Classification of hazardous areas
The classifications of hazardous locations depend on the types of materials handled. Currently there are two main codes used by the industry to certify EX forklifts – the US NEC and the International Electrotechnical Commission (IEC), used by Europe and accepted worldwide.

The classification system used in Europe – followed by many other countries: workplaces are classified into zones.
According to European directive ATEX 1999/92/EC, hazards associated with gases or vapours are classed either in zones 0, 1 or 2.
Hazards associated with powders or dust particles are categorised as zones 20, 21 or 22.
In the USA, the division classification system consists of
class 1 for flammable gases, vapours and liquids, further subdivided into divisions 1 & 2, groups B, C, D;
class 2 for combustible dusts, subdivided into divisions 1 & 2, group G;
class 3 for ignitable fibres and flyings, subdivided into divisions 1 & 2.
The National Electrical Code (NEC) establishes the requirements for electric forklifts used in the division classifications.
Explosive atmospheres are classified according to the frequency and duration of the occurrence of hazardous explosive atmospheres in zones.

 

      Zone  Description
0 Explosive gas atmospheres or long consecutive sites, Gas or vapour is present all of the time, over 1000 hours/year or >10% of the time
1 Gas, vapour or mist will be present or expected to be present for long periods of time under normal operating conditions, 10–1000 hours/year or 0.1–10% of the time.
2 In normal operation, there could be no explosive atmosphere, if there is place for occasional and is only there for a short time; unwanted substances should only be present under 10 hours/year or 0–0.1% of the time
20 A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, or for long periods or frequently
21 A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur, occasionally, in normal operation.
22 A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation but, if it does occur, will persist for a short period only.
 
 
In the zones, the probability of the effectiveness of ignition sources must be reduced.
Zone 2 / 22: it is sufficient if the devices do not have any operational sources of ignition.
Zone 1 / 21: for devices with danger of ignition, the effectiveness of ignition source prevention must not be impaired even when an error occurs.
Zone 0 / 20: in the design of the devices, also very rare error, which could be a source of ignition must be eliminated.
 
Safe area on chemical and other plant are present where the hazardous gas is diluted to a concentration below 25% of its lower flammability limit (or lower explosive limit (LEL)).

Relevant for the classification of zones are the parameters explosion limits, releasable material quantities and flow of ventilation and - if necessary – the monitoring devices being used. However, the amount of releasable material and the probability and duration of the spill is often difficult to quantify.

Gas groups

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 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.
Group Representative Gases
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
 
Classes and levels The ignition temperature of gases is used to define classes and levels
 
T1 T2 T3 T4 T5 T6
methane; fire-damp; methyl hydride marsh gas
ⅡA Ethane, propane and acetone,
Styrene, vinyl chloride, chlorobenzene,
Toluene, methanol, benzene, chlorine,
Carbon monoxide, ethyl acetate,
Acetate, acrylic
Butane, ethanol, propionic acid,
N-butanol, amyl acetate esters,
Acetic anhydride
Pentane, hexane, heptane,
Decane, octane, gasoline,
Hydrogen sulfide, cyclohexane
Ether,
Acetaldehyde
Nitrous acid
Ethyl ester
ⅡB Dimethyl ether, commercial gas,
Cyclopropane
Ethylene oxide, epoxy propane, butadiene, ethylene Effects of isoprene
ⅡC Water gas, hydrogen,
Coke oven gas
Acetylene Carbon disulfide Nitric acid ethyl ester
 
 
Apparatus marked IIB can also be used for IIA gases. IIC marked equipment can be used for both IIA and IIB. If a piece of equipment has just II and no A, B, or C after then it is suitable for any gas group.
A list must be drawn up of every chemical gas or vapour that is on the refinery/chemical complex and included in the site plan of the classified areas. The above groups are formed in order of how volatile the gas or vapour would be if it was ignited, IIC being the most volatile and IIA being the least. The 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.

Equipment Protection Level (EPL)

In recent years also the Equipment Protection Level 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 of protection
I (mines) energized   Ma  
I (mines) de-energized 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  
III (dust) explosive surface between 10 and 1000 hrs/yr 21 Db  
III (dust) explosive surface between 10 and 10 hrs/yr 22 Dc  

Temperature classification

Another important consideration is the temperature 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 degree Celsius):
USA°C UK °C Germany °C
Continuous - Short Time
T1 - 450 T3A - 180 T1 - 450 G1: 360 - 400
T2 - 300 T3B - 165 T2 - 300 G2: 240 - 270
T2A - 280 T3C - 160 T3 - 200 G3: 160 - 180
T2B - 260 T4 - 135 T4 - 135 G4: 110 - 125
T2C - 230 T4A - 120 T5 - 100 G5: 80 - 90
T2D - 215 T5 - 100 T6 - 85  
T3 - 200 T6 - 85    
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.

Auto-ignition temperatures (vapours & gases)

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:
Gas Temperature

Methane 580 °C
Hydrogen 560 °C
Propane 493 °C
Ethylene 425 °C
Acetylene 305 °C
Naphtha 290 °C
Carbon disulfide 102 °C
 

The surface of a high pressure steam pipe may be above the autoignition temperature of some fuel/air mixtures.
Types of protection
 
Ignition protection type   description
Explosion-proof
Flameproof enclosure
 
d the components, which may cause an ignition, are installed in a casing that can withstand the pressure of the explosion. The openings of the casing are designed to prevent transmission of the explosion to the outside. can ensure the internal flame of gas travels through the gap, reducing the energy, not enough to detonate outside the shell of gas.
Increased safety e During normal operation without arcing, sparks and hazardous high-temperature, further protective measures with regard to structure, improving the security and reliability of the device.
the emergence of Sparks, arcs or improper temperatures, which could act as a source of ignition is prevented by additional measures and an increased level of safety.
Positive pressure type
Pressurization
p Shielding gas pressures higher than around keeping in order to avoid explosive mixtures into the enclosure or an adequate protective gas by shell, the explosive mixture of concentration within the lower explosion limit less.
the housing of the equipment is filled with a flammable protection. Pressure is held upright, so that can get an explosive gas mixture not to the possible ignition sources arranged inside the housing. If necessary, the housing is constantly flushed.
Intrinsically safe Intrinsic safety i Circuit within the device under the conditions laid down, under normal working or under fault conditions produce sparks and heat do not ignite explosive mixtures.
the supply of the electrical equipment runs over a safety barrier that current and voltage as far as limited, do not achieve the minimum ignition energy and ignition temperature of an explosive mixture. The resources divided also into Ex-ia for ex-zone 0 or 1, and ex-ib for ex-zone 1 or 2.
Encapsulation m It will not ignite explosive mixtures of arc, spark or high-temperature part of the cast, so that it cannot ignite explosive mixtures around.
the parts of the electrical equipment, which can produce ignition sources, are embedded in casting compound so that an arc not to an explosive mixture outside the containment can walk through.
Structural safety
(constructional safety)
C
 
type of protection only for non-electrical equipment. The devices are designed so that they have no ignition sources during normal operation. The risk of occurrence of mechanical failures that can lead to the emergence of sources of ignition, is reduced to a very low level. See EN 13463-5.
Oil encapsulation
(protection by oil immersion)
o the parts of the electrical equipment where an ignition can assume, are immersed in a protective liquid (usually oil).
 
protection by powder filling q the equipment is filled with fine-grained sand. A possible arc is cooled so far that the ignition of an explosive mixture is excluded. The surface temperature must not exceed the limit.
 
Ignition protection method
non-incendive, non-sparking)
n during normal operation and when custom errors no ignition hazard posed by the electrical equipment.
Through technical measures, it must be ensured that no sources of ignition can act according to the classification of a subordinate explosive mixture (gap width, temperature class).
 
 
There are several technical ways, to reach the explosion protection of electrical equipment. The ignition protection types are listed in the table.
The ex marking of a device called the ignition protection type with the first letter of the type of protection.
 
Temperature classes
Devices and equipment may be operated only in an explosive atmosphere, if their maximum surface temperatures below the ignition temperature of the surrounding explosive mixture. Simple assessment, temperature classes were defined, in which the instruments according to the maximum temperature are divided. The individual mixtures are mapped to the corresponding temperature classes (T1 to T6). When determining the temperature class of an equipment, the maximum permissible ambient temperature is to note it is exposed, since this has an influence on the temperature of the accessible device. In the respective standards is set, the safety distance between the flash point and the temperature of the device is.
The ignition temperature for a layer (A value) and a cloud (B value) is determined for dusts. The permissible surface temperature is calculated from the minimum of the two values (A −75 ° C) or 2/3 * B.
Temperature classes
Temp.
class maximum
Temp. Fabric samples (see also ATEX)
 
T1 450 ° c. carbon monoxide, methane, propane, hydrogen
 
T2 300 ° C acetylene, cyclohexane, ethylene
 
T3 200 ° C diesel, gasoline, hydrogen sulphide
 
T4 135 ° C acetaldehyde, ethyl ether (no other substances)
 
T5 100 ° C no materials
T6 85 ºc only carbon disulphide
 
Potentially explosive atmospheres (other than mines)
1 To 3 is divided into categories according to the ATEX Directive 94/9/EC.
The letter "G" stands for gas, "D" stands for dust.
In IEC 60079-0 and thus authorisations according to the IECEx equipment protection levels (EPL) are schema (German: equipment protection level) defined.
Equipment of category 1 g / 1 d or EPL GA / da are to such a way that they provide a very high level of security. Instruments of this category must ensure the necessary level of security also for rare disorders. Also at the occurrence of two errors on the device, it must not come to an ignition.
They may be used in zone 0 (category 1 g) and zone 20 (category 1 d).
 
Equipment of category 2 g / 2D or EPL GB / DB must be such, that they ensure a high degree of security. Devices of this category must ensure the necessary level of security when frequent and usually foreseeable errors (defects on the unit) and avoid sources of ignition.
You may not in zone 1 (category 2 or zone 21 (category 2D) are used.
 
Equipment of category 3 g / 3D or EPL GC / DC are to such a way that they provide a normal level of security. Devices of this category have foreseeable faults (defects on the unit) guarantee the required level of security and avoid sources of ignition.
They may be used in zone 2 (category 3 g) or zone 22 (category 3D).
Classification of devices that can be used in potentially explosive zones
Group
Devices that are suitable for use in potentially explosive atmospheres are divided into three groups. Until the introduction of the EN 60079-0:2009, only two groups were divided.
Group I
stands for at risk of firedamp mines (coal mining). It depends of each explosive substance. The risk is increasing from A to C.
Group II
stands for explosive gases and is divided into subgroups IIA, IIB and IIC for some types of protection (ex i ex d, ex n).
With ex d (flameproof enclosure):
The letter reflects the border gap width (maximum width of gap of a flame fail-safe device through the ignition can be transferred) of the device.
For ex i (intrinsically safe) this is the energy in the intrinsically safe circuit.
With ex n This is differentiated, as this depends on the type: ex nA or ex nL (Note: ex nL, ic will be replaced by ex).
A subgroup associated diesel, gasoline, ethane, methane, carbon monoxide.
Subgroup B includes for example gas, hydrogen sulfide, and ethylene.
The subgroup C summarizes hydrogen, acetylene and carbon disulphide.
Group III
Dust, which is here divided (fibers) IIIA, IIIB (non-conductive dusts) and IIIC (conductive dusts). This group is introduced in the standard, the ATEX Directive 94/9/EC II differs only in Group I and group.
Device categories in Europe
Marking
It is indistinguishable in marking according to the applied standards (E.g. IEC 60079-0, EN 60079-0) and rules through directives (ATEX Directive) or legal requirements/regulations (E.g. national electrical code (NEC) in the United States).
Marking according to ATEX Directive 94/9/EC
 
Marking of equipment for use in potentially explosive atmospheres to ATEX product Directive 94/9/EC
The ATEX Directive 94/9/EC requires:
• "Ex-sign" ATEX logo (epsilon chi in the hexagon)
• Device group ('I': mining, "II": all other areas)
• Category as defined in ATEX Directive 94/9/EC (1 g, 2 g, 3 g, 1 d, 2D,3D)
• Marking according to the applied standards
(has been abbreviated in accordance with EN 60079-0 until 12/2004 with "EEx" 50014 and EN, with the acquisition of the IEC standard as EN-norm "Ex")
• CE mark (see also CE-marking)
Note
Markings for gas and dust are not to combine.
Web links
• Explosion protection information of BG Chemie
• Explosion protection information of the PTB (Physikalisch-Technische Bundesanstalt)
• Directive 94/9/EC on equipment and protective systems intended for use in potentially explosive atmospheres (ATEX)
• Directive 94/9/EC: transposition into national law
 

 

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
  Ex Code Description Standard Location Use
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" propane/ethylene, 0.004" 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 Heavy current equipment
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 can not come in contact with energized 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)
IEC/EN 60079-25
IEC/EN 60079-11
IEC/EN60079-27
'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 Non-Incendive Concept (FNICO) (zone 2)
IEC/EN 60079-15
IEC/EN 60079-27
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 Manufacturers Certification. 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 the one independent component faults simultaneously.

Labeling
All equipment certified for use in hazardous areas must be labelled to show the type and level of protection applied.

Europe
In Europe the label must show the CE mark and the code number of the certifying body. The CE marking is complemented with the Ex mark, followed by the indication of the Group, Category and, if group II equipment, the indication relating to gases (G) or dust (D). For example: Ex II 1 G (Explosion protected, Group 2, Category 1, Gas) Specific type or types of protection being used will be marked.

  • EEx ia IIC T4. (Type ia, Group 2C gases, Temperature category 4).
  • EEx nA II T3 X (Type n, non-sparking, Group 2 gases, Temperature category 3, special conditions apply).
In the United Kingdom, industrial electrical equipment for hazardous area has to conform to standard BS 60079 and in some cases, certified as meeting that standard. Independent test houses (known as Notified Bodies)are established in most European countries, and a certificate from any of these will be accepted across the EU. The DTI appoint and maintain a list of Notified Bodies within the UK, of which Sira and Baseefa are the most well known.
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