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Hazardous Locations Design Consulting


Hazardous
Locations
Interactive
Encyclopedia
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Glossary


Welcome to our Hazardous Locations Interactive Encyclopedia!

Better than a simple glossary, our unique Encyclopedia offers useful information on a wide range of hazardous locations terminology, making you an expert in no time! We hope you find it a useful reference.

A   B   C   D   E   F   G   H   I   J   K   L   M   N   O   P   Q   R   S   T   U   V   W   X   Y   Z

A

AEx: Refers to equipment rated for United States Zone requirements. It is an adaptation of the international Ex marking.

Agent: Usually refers to the person at a certifications agency who is performing the certifications services i.e. a certifications engineer or technician. Better referred to as a "certifications agent". Sometimes "agents" are more properly referred to as "certification engineers", though not all are engineers.

Agency: See certifications agency.

Area classification: Hazardous locations are divided into different areas corresponding to the risk of ignition. Area classification is the practice of identifying and rating the physical spaces involved as hazardous locations and assigning them the correct Division and/or Zone rating according to the Division scheme and/or the Zone scheme. Note that hazardous locations are ranked by the risk of ignition according to how often an explosive atmosphere may be present. The consequences of an ignition - the potential damage or risk to life or property - is not usually taken into account, but might be addressed during a HAZOP or separate risk analysis. The Equipment Protection Level (EPL) method was introduced, in part, to help improve this situation by adding an element of risk analysis to area classifications.

Associated apparatus: Specific to intrinsically safe equipment, associated apparatus is equipment that hooks up to your IS equipment, but is not itself intrinsically safe. Associated apparatus might be OK for use in the hazardous location, or it may need to be installed outside the hazardous area. Examples include an explosion-proof power supply for an intrinsically safe device, or an intrinsically safe barrier barrier, installed outside the hazloc area, which provides power to intrinsically safe apparatus.

ATEX: The name for the hazardous areas legislation of the European Union (EU), as opposed to Canadian, United States, or internationally-based (IEC) regulation. ATEX is mandated by the ATEX Directive. See the Library entry Understanding ATEX for more information.

ATEX Directive: European Union Directive 2014/34/EU, called the "ATEX Directive" for short. This is the EU law that mandates compliance to the ATEX system for hazardous locations. Sometimes called ATEX 95, as it implements Article 95 of the EU treaty. Simplistically put, ATEX 95 covers what equipment manufacturers must do, while ATEX 137 covers what end users must do. See the Library entry Understanding ATEX for more information.

Authority having jurisdiction: Whoever is respnsible for approving equipment for use in hazardous locations. Knowing who the relevant authority is can be difficult because enforcement might be done by any of several authorities, depending on where you are in the world. Most of the time it is an electrical inspector of some kind.

Autoignition temperature (AIT): The temperature at which a potentially explosive atmosphere will ignite. AIT is related to the temperature code of hazardous locations products.

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B

Barrier: An electrical circuit that is designed to limit voltage, current and/or power to following circuits. A barrier can be stand-alone or integrated into a larger product or system. A stand-alone device is sometimes called an "intrinsically safe barrier" or "non-incendive barrier" according to its purpose.

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C

Capacitive ignition / Capacitive spark ignition: The ability for electrical energy stored in capacitors to ignite an explosive atmosphere. This can occur if the capacitors are discharged (shorted out) and an arc or spark occurs. Capacitive ignition is sometimes considered in conjunction with current ignition because a power source is required to charge the capacitors. See spark ignition and current ignition.

Certifications agency: A general term for an organization that tests and evaluates products against published national and international standards to ensure compliance. Agencies are usually an NRTL, Certification Body, a Notified Body and/or an IECEx Certification Body (ExCB), empowered by governments or other organizations to perform these services within a specific scope and/or country. Agencies may only evaluate products to standards within their authorized scope. Most agencies were originally organized either by insurance associations (to reduce insurance losses) or national governments (to promote public safety). The term "certifications body" is sometimes used synonymously.

Certifications agent: Usually refers to the person at a certifications agency who is performing the certifications services i.e. a certifications engineer, inspector or technician. The term "certifications engineer" is possibly more correct, except that certification agents are not always engineers. "Certifications agent" might also refer to a project manager, account manager or salesperson who is helping the client through the certifications process.

Certification Body: A designation granted to organizations by the Standards Council of Canada (SCC). An Certification Body is accredited by the SCC to evaluate products against nationally recognized safety standards. In the United States, the equivalent organization is called a NRTL; in the EU, they are called Notified Bodies; internationally, they are called IECEx Certification Bodies (ExCB). These four types of organization are not equivalent, and only Certification Bodies can grant certifications for products used in Canada, but several NRTLs, Notified Bodies and ExCBs are also Certification Bodies.

Certification scheme: A way of managing and minimizing the risks of hazardous locations. Schemes usually involve determining fuel types (gas, dust, solids), their ignition characteristics (spark and heat), the degree of risk (area classification), identifying protection methods suitable for these risks, establishing standards to which equipment can be evaluated and certified and establishing codes and operational practices that must be followed when installing, operating, maintaining and repairing the equipment. This ensures that only properly constructed equipment is used in hazardous areas. There are two principal schemes: the Division system, used in most United States and Canadian facilities, and the Zone system which is used in all of Europe, all new Canadian installations, a rare few new United States installations and most other locations globally. The IEC has been working on a universal "Ex scheme" for decades, but adoption has been slow.

Class: In the Division scheme, the Class indicates the fuel type. Class I fuels are gases, Class II covers dusts, and Class III covers fibers and flyings. Any of these kinds of fuels can become highly explosive when mixed with air.

Class I: In the Division scheme, Class I covers fuels that are gases or vapors. Class I areas may include "obvious" areas such as mining (firedamp), oil refineries, natural gas facilities, and fuel stations. It can also apply to many other diverse industries that use, produce or store flammable gases. The equivalent Zone system designation is Class II, which can be confusing.

Class II: In the Division scheme, Class II covers dust fuels, which can be extremely explosive when suspended in air. The "iPad factory explosion" of 2012 was caused by aluminum dust generated from the polishing process. Other industries include mills for flour, sugar, and grain, woodworking shops, chemical and powder manufacturing facilities and coal dust in underground mines. Without due care, finely-ground product can settle in ceilings and other generally unobserved areas, where it remains until ignited. Dust explosions can be especially powerful, and can occur repeatedly after any event that stirs up the dust, such as a gas explosion. The equivalent Zone system designation is Class III, which can be confusing.

Class III: In the Division scheme, Class III covers fibers and flyings, such as cotton, rayon and nylon. Fibers can escape during many parts of the process, including storage, transport, sampling, and fabrication; they mostly pose a fire risk rather than an explosion risk per se. Comparatively speaking there does not seem to be a lot of equipment solely rated for Class III locations.

Classified location: Another term for hazardous location .

Clearance: The distance between two points as measured through space or air. Clearance distances are related to the ability of electricity to arc across gaps. Clearance distances are normally considered along with creepage distances.

Cold resistance: The minimum resistance of a fuse, measured at the minimum ambient temperature. Usually lower than the fuse resistance quoted on the data sheet. Some fuse makers quote their "cold resistance" at 25*C, which is confusing.

Compliance Union (CU): A trade agreement between Russia, Belarus and Kazhakstan that harmonizes the requirements for various products. Created in 1999 and fully in force in 2013, the CU scheme replaces the old GOST-R, GOST-B and GOST-K schemes for these countries. Similar to EU regulations, products for the CU must bear the EAC (EuroAsian Conformity) mark and can be imported into any CU country without further restriction.

Countable fault: A special term referring to the kinds of conditions that can be imposed on an intrinsically safe product for evaluation purposes. I.S. rules permit the imposition of a certain number of "countable" faults. Usually only two are permitted, hence each one is "counted" towards the allowable limit. This is as opposed to non-countable faults, where an unlimited number of faults can be imposed. "Countable" faults are usually imposed only on infallible devices, and are sometimes limited to specific kinds of failures according to the infallible device in question. See non-countable fault.

Creepage: The distance between two points as measured across a physical surface. Creepage distances are related to the ability of electricity to "track" across the surface of materials such as plastic, and is sometimes called "tracking" for this reason. Creepage is normally considered along with clearance.

Current ignition / Current spark ignition: The ability for electrical energy travelling as a current to ignite an explosive atmosphere. This can occur if the current is interrupted (broken) and an arc or spark occurs. See spark ignition and capacitive ignition.

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D

Derating: The practice of over-rating critical componets is called "derating". (This might be more clearly written "de-rating", but is rarely so written.) For intrinsically safe products, nearly all components that provide protective functions must be derated to ensure long-term reliability. Most components must be rated for 150% of the actual applied voltage, current, or power; such components are also said to be "2/3 derated".

Directive: Refers to the high-level laws of the European Union (EU). EU membership countries adopt Directives, which are then voted into law in each individual country. Equipment intended for hazardous locations must comply with Directive 2014/34/EU, called the ATEX Directive. There are many other Directives that cover item such as machinery, medical devices and a host of other products.

Division: Can refer to either the Division scheme of classifying hazardous areas (as used in North America), or an area that is classified as Division 1 (most hazardous) or Division 2 (less hazardous) under that scheme. In Europe and internationally, the corresponding term is Zone. For more information, see the Library entry "Understanding Zones and Divisions".

Division system: A way of classifying hazardous areas and rating equipment for use in those areas; a certifications scheme. The Division system may still be used in the United States, and was used in Canada until recently, so thousands of existing installations still use the Division system. The corresponding (but different) system used in the EU and most of the rest of the world is the Zone system.

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E

Encapsulation: A protective layer of hard or semi-hard material that is poured into place, or a reference to the poured coating; also called "potting". Encapsulation is often applied to circuits for physical or electrical protection. The type 'm' protection technique involves total or near-total encapsulation of electrical devices as a protection technique. It can also be applied in intrinsically safe circuits to restrict energy release, making it highly useful for specific situations.

Equipment Protection Level (EPL): A way of rating equipment according to their safety in hazardous locations. In theory, EPL is different than the Division or Zone rating of the equipment, though it is related. Divisions and Zones only take the probability of ignition into account, and not the potential consequences, so they do not form a complete risk analysis. EPLs were introduced to give operators and installers options where the risk of an explosion might be considered unusually high or unusually low. In practice, though, EPLs are direcly related to the Division/Zone ratings because operators and inspectors will never take on the risk of approving lesser equipment, even if the consequences of an explosion are very small.

Ex: Can refer to: explosion-protection equipment (i,e, "Ex equipment", equipment rated for hazardous locations use, or the hexagonal "Ex" graphic used to mark and identify Ex equipment in Europe. In the United States, the equivalent term is AEx. In Europe, EEx was used previously, but not any more. "Ex equipment" can mean any hazloc-rated equipment, not just explosion-proof types.

EEx: The older designation for Ex equipment meeting European standards. Now obsolete, replaced with Ex. (Also see AEx.)

ExCB: IECEx Certification Body, a designation granted to organizations that are accredited to certify to the IEC hazardous locations standards. In the USA, equivalent organizations are called NRTLs; in CanadaCertification Body; in the EU, they are called Notified Bodies. These various types of organization are not equivalent, and only ExCBs can grant certifications according to IEC standards.

Explosion-proof: A protection technique that allows ignition to occur, but safely contains and quenches the flame front to prevent the explosion from propogating out of a limited area. Similar to the European "flameproof", but not identical.

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F

Flameproof: A protection technique that allows ignition to occur, but safely contains and quenches the flame front to prevent the explosion from propogating out of a limited area. Similar to the North American "explosion-proof", but not identical.

Fault: A special term referring to the kinds of conditions that can be imposed on a product for evaluation purposes; often applied to intrinsically safe and encapsulated equipment. A "fault" may or may not be a realistic malfunction; the I.S. standards permit certification agencies to "fault" nearly anything imaginable to nearly any imaginable condition, including dead short, open-circuit or anything in between. Only infallible devices are exempt from general faulting, and most "infallible" components can still be faulted in specific ways. Faults are imposed for the purposes of establishing the worst case. See countable fault and non-countable fault.

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G

Group: Explosive gases are classified into groupings, or "Groups" according to their minimum igniting energy. All the gases within a Group have similar MIE, which means they all have about the same probability of being ignited by an arc or spark. The Division system has 4 gas groups (A, B, C and D) and 3 dust groups (E, F and G). The Zone system has three gas groups (IIA, IIB, and IIC), three dust groups (IIIA, IIIB and IIIC) and one group specifically for mining (Group I). Groups A and IIC are the worst for each gas system, which can be confusing because they are backwards compared to each other. "Group" is typically capitalized when used to identify a specific gas group (i.e. "Group A") but otherwise not (i.e. "gas groups").

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H

Hazardous location: A physical area where an explosive atmosphere may be present. Can also be called a classified location, or "hazloc" for short. "Hazardous location" specifically means an explosive atmosphere, and not any other property or situation that might pose a danger to people or property. Hazardous locations are divided into different areas corresponding to the risk of ignition - see area classification .

Hazloc: Short way of writing "hazardous location".

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I

IEC: International Electrotechnical Commission, an international organization dedicated towards establishing standards for electrical and electronic equipment. As one of the longest-running independent organizations, they have produced several hundred such standards, and have seen them adopted worldwide. What "IEC" refers to in hazloc terms is the hazloc standards written and published by the IEC for use by the international community. The IEC standards provide the basis for a lot of the other standards, including ATEX.

Inductive ignition / Inductive spark ignition: The ability for electrical energy stored in inductive coils to ignite an explosive atmosphere. This can occur if current in the inductors is interrupted (open circuited) and an arc or spark occurs. Inductive ignition is usually considered in conjunction with current ignition and capacitive ignition because a power source is usually present. See spark ignition, current ignition and capacitive ignition

Infallible: An "infallible" device is one that is considered highly reliable for the purposes of intrinsically safe design. Infallible devices are usually derated to ensure robust operation and long-term reliability. "Infallible" does not actually mean "not subject to failure", and infallible devices can still have countable faults imposed on them to establish the worst case situation. The types of failures imposed by countable faults may be limited - for example, an infallible current-limiting resistor might only be considered to fault to an open-circuit condition.

Infallible resistor: A resistor so rated and constructed as to not be subject to short-circuit failure. Such a resistor can only be faulted with a countable fault or not at all, and never to a resistance lower than it's normal minimum.

Ingress protection (IP) rating: A description of how a product resists the ingress of solids and water. The first digit indicates solids (i.e. IP5x) and the second water (IPx6). As "solids" covers both large items (hands and fingers) and small items (dust), IP indicates the degree of safety for both equipment and personnel. IP54 is the de-facto minimum for most Ex equipment, but a lot of industrial equipment is rated IP65 or better.

Intrinsic safety (IS): Noun: A protection technique that limits the amount of electrical energy in a product to prevent ignition of a potentially explosive atmosphere. Often called "I.S." or IS for short.

Intrinsically safe (IS): Adjective: A product or system that conforms to the requirements of intrinsic safety for hazardous locations is said to be intrinsically safe. Can also be called "I.S." or IS for short. Intrinsically safe equipment is designated type 'i' in the Zone system of classification. Strictly speaking, there is no "type 'i'" in the Division system, but sometimes people refer to Division-style intrinsically safe equipment as type 'i' anyway.

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J

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K

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L

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M

Maximum experimental safe gap (MESG): The biggest gap between two metal plates (in a specific test apparatus) through which an explosion will not propogate to the outside world. Explosion-proof and flameproof equipment tries to keep all joints below the MESG so that if an explosion occurs inside, it is safely contained. The MESG will change according to the joint length and configuration.

Minimum igniting energy (MIE): The amount of electrical energy needed to ignite an explosive atmosphere. Varies according to temperature, pressure, fuel, mixture, turbulence, velocity and a bunch of other factors. MIE is related to the gas group of the fuel, which indicates how easily the fuel is ignited by spark ignition. Gas grouping is separate from temperature code (T-code) because the autoignition temperature (AIT) of a gas is not related to the MIE, making the risk of thermal ignition very different from the risk of spark ignition.

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N

New Legislative Framework (NLF): The New Legislative Framework is a package of changes to existing EU Directives. The NLF is essentially a "Revision 1" package for the existing laws. The NLF was initiated in 2008 but entered into force in about 2015. Major changes include establishing agency accreditation to help even out the expertise of Notified Bodies, and market surveillance and monitoring to ensure that everything that is CE marked is, in fact, in compliance. Strangely, and perhaps naively, the EU did not require these things before, apparently trusting that Member States will simply do the right thing. Uber-boring details about the changes can be found here.

Non-countable fault: A special term referring to the kinds of conditions that can be imposed on an intrinsically safe product for evaluation purposes. Unless the design includes special and specific features, agencies are allowed an unlimited number of "non-countable faults" to impose against the design. This means that all "ordinary" components, tracks, wires and spacings can be arbitrarily changed to open-circuits, dead shorts, or anything in between, and the effects assessed. These faults are "non-countable" because they do not count against any defined limit; agencies can impose as many as they want. Only infallible components are immune from non-countable faults, but they can have countable faults (usually up to 2) assessed against them. See countable fault.

Non-incendive equipment: Equipment for use in the Division system that is safe in hazardous areas when the equipment is operating normally. Non-incendive is sort of like "intrinsic safety light", as it includes most of the same principles but is not nearly as demanding. As non-incendive equipment is less reliable, it is only allowed in relatively low-risk (Division 2) locations. The corresponding European protection type was type 'nL', but is now intrinsically safe type 'ic'.

Notified Body: An independent company or corporation within Europe that is authorized to evaluate products for compliance to EU Directives. Notified Bodies must have offices within the EU and be licensed by an EU government to perform these tasks. Oddly enough, under the original ATEX Directive, Notified Bodies were not subject to any independent oversight, though that appears set to change. In the United States, these organizations are called NRTLs; in Canada, they are called Certification Bodies; in IECEx, they are called an Certification Bodies (ExCB). These various types of organization are not equivalent, and only Notified Bodies can grant certifications for products used within the EU.

NRTL: Nationally Recognized Testing Laboratory/Laboratories, a designation granted to organizations by OSHA in the United States. An NRTL is accredited by OSHA under Federal code 29 CFR 1910.7 to evaluate products against nationally recognized safety standards. In Canada, the equivalent organization is called a Certification Body; in the EU, they are called Notified Bodies; in IECEx, they are called an Certification Bodies (ExCB). These various types of organization are not equivalent, and only NRTLs can grant certifications for products used within the United States.

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O

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P

Potting: See encapsulation.

Positive temperature coefficient (PTC) device: A form of resettable fuse to limit current. PTCs self heat and exhibit a rapid increase in resistance at a critical temperature. These devices are not recognizd in most standards, making them only useful for hazloc purposes in rare and narrow circumstances.

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R

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S

Safety factor: A margin of safety applied to equipment evaluations to account for un-measureable or unknown elements in the design, which forces the designer to over-design the equipment.

Spacings: Normally refers to both creepage and clearance distances. A bit of an older term, "spacings" (creepage and clearance distances) determine if separation between circuit elements can be defeated by the imposition of non-countable faults, countable faults, or not at all. Most "ordinary" wiring and PCB layouts can be faulted using non-countable faults, which are unlimited.

Simple apparatus: In intrinsic safety, "simple apparatus" is anything that doesn't generate or store more than 1.2V, 100 mA, 25 mW or 20 uJ. Simple apparatus generally needs no special protection and is automatically qualified as intrinsically safe. Devices like LEDs, thermocouples, RTDs, strain gauges and switches are often simple apparatus. Note that to qualify, only the simple apparatus can extend into the hazardous area, and it has to be electrically isolated from whatever it is connected to. As soon as you connect or integrate "simple apparatus" into a larger circuit, it is no longer simple.

Spark ignition: The ignition of an explosive atmosphere by an electrical arc or spark. The spark is usually considered to be a momentary, near-instantaneous delivery of energy, but sustained arcs are sometimes possible. Simplistically, if the spark delivers more energy to the fuel than the minimum ignition energy (MIE) of the fuel mixture, the fuel will ignite.

Standard: In hazardous locations, a standard is a published document adopted by industry, governments or users in order to establish safety or performance requirements for equipment. Standards can be written by various independent bodies, usually non-governmental, such as certification agencies, industry bodies and national and international non-profit groups. Local and national governments often vote standards compliance into law, and insurance coverage might be contingent upon conforming to standards.

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T

Temperature code (T-code): Many hazardous locations products are given a temperature code (T-code) that describes their potential to ignite explosive materials by thermal ignition. T-codes range from T1 to T6, and refers to a specific maximum temperature the product may reach. Users can compare the T-code against the autoignition temperature (AIT) of their potentially explosive materials to decide if the equipment is safe to use or not. T-code is separate from gas groups because the AIT of a gas is not related to the minimum ignition energy (MIE), making the risk of thermal ignition very different from the risk of spark ignition. Various standards and industries have adopted specific T-codes for equipment, either due to technical necessity or due to competitive pressure.

Thermal ignition: The ignition of an explosive atmosphere by a hot surface. As all physical materials have a finite heating time, thermal ignition is usually considered to occur after a period of time, though not necessarily a long period of time. This is as opposed to spark ignition which is considered to happen suddenly and instantly. Simplistically, if the hot surface exceeds the autoignition temperature of the fuel, the fuel will ignite.

Type: The ATEX/IEC term for a protection method. Each protection method is given a letter code, such as "i' (intrinsic safety). An intrinsically safe system is then referred to as a "type 'i'" system, with the letter usually bracketed in single or double quotes. Various types include 'i', 'd', 'o', 'm', 'e', 'p' and 's'. Some "types" are related to similar North American methods, but not all.

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U

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W

Worst case: Refers to the most unfavorable set of circumstances possible, usually established by imposing allowable faults on the design. Certifications agents love the worst case, and almost always default to it when evaluating equipment as a means to ensure safety. Designers hate the worst case because it makes life hard, and is sometimes so vanishingly unlikely as to be nearly laughable. In such conflicts, the certification agents almost always win.

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X

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Z

Zone: Can refer to either the Zone scheme of classifying hazardous areas (see Zone system), or an area that is classified as a hazardous locations Zone. There are three Zones for gaseous fuels (0, 1 and 2) with 0 being the most risky and 2 being the least risky. There are also three Zones for dust fuels (Zone 20, 21 and 22), with Zone 20 being the most risky. In North America, the corresponding term is the Division. For more information, see the Library entry "Understanding Zones and Divisions".

Zone system: A way of classifying hazardous areas and rating equipment for use in those areas; a certifications scheme. The Zone system has been used nearly everywhere for decades, except the United States and Canada. Canada recently changed to the Zone system, but the United States has not, and thousands of existing installations in North America still use the Division system as a result.

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