Explosion-proof equipment gives you peace of mind daily working in a hazardous area. However, even the tiniest spark produced within a hazardous environment can result in immeasurable damage. In this way, working with explosion-proof equipment is not only an investment but also safe. In this post, we separate some reasons to work with explosion-proof equipment and see the benefits and the application scenarios.
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Let&#;s start by defining what makes equipment explosion-proof. If your equipment bears the UL certification seal, it is ready and approved for use in hazardous environments. However, be careful to use your ex-proof equipment within the designated area classification. To understand how the ratings work, read our previous post: Explosion-Proof Motor: Learn to identify the ratings.
The explosion-proof enclosure acts as a cooler to prevent the explosion from reaching the dangerous atmosphere of the environment. Therefore, regular equipment maintenance will ensure excellent protection in explosive accidents.
In the image above, you see a representation of the cooling done in the explosion-proof housing of the equipment that contains the pressure of gases. Now let&#;s look at some of the benefits of working with this rugged equipment.
Using explosion-proof equipment will reduce the risk of more significant damage in your hazardous area. As the equipment is capable of containing internal explosions, this keeps your work area safe and prevents other equipment damage. To visualize this benefit, picture the following scenario. When using an ex-proof motor, a buildup of flammable dust ignites its casing and results in an explosion. However, the case prevents the damage from being greater in the hazardous environment. Thus, in addition to preserving the safety of staff, this safety measure also eliminates the risk of greater financial losses.
To deliver durability and strength, the materials used to manufacture explosion-proof equipment must be of the best quality. For example, imagine a junction box for electrical use inside an explosive environment; its material needs to be resistant to contain and cool a possible explosion or fire. In this way, explosion-proof equipment has a longer shelf life, establishing an investment with long-term benefits.
Undoubtedly one of your daily goals is to increase productivity in your work routine. Investing in safety measures can increase productivity. With the right equipment, your staff will have less work training for hazardous areas operations. For example, an explosion-proof headlamp becomes very practical for a miner who needs to focus on their service. As a result, they do not commit one of their hands to work and don&#;t waste the workforce. To further optimize the work, in this case, the installation of explosion-proof light fixtures and the arrangement of portable light also increase productivity in confined environments.
One of the most significant benefits that the use of explosion-proof equipment can bring is the recognition of a high standard of service. Keeping a hazardous area under control requires investment and knowledge. Training your staff and the right equipment will increase the value and quality of your service and product. Having your efforts recognized in the market is certainly attractive to you! So, put together the best safety strategy using explosion-proof equipment.
In this post, you saw some reasons why integrating explosion-proof equipment in your hazardous area is beneficial. Ensure the safety, quality, and productive growth of your industry. Some of the practical examples mentioned in this article show optimistic scenarios using ex-proof equipment to improve work performance. Those types of equipment make part of our catalog. The Intrinsically Safe Store prioritizes high safety standards, and here you will find the best safety measure. Our intrinsic safety experts will guide you to the best safe control solution for your hazardous area. Do not hesitate to contact us; we are ready for you!
In electrical and safety engineering, hazardous locations (HazLoc, pronounced haz·lōk) are places where fire or explosion hazards may exist. Sources of such hazards include gases, vapors, dust, fibers, and flyings, which are combustible or flammable. Electrical equipment installed in such locations can provide an ignition source, due to electrical arcing, or high temperatures. Standards and regulations exist to identify such locations, classify the hazards, and design equipment for safe use in such locations.
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A light switch may cause a small, harmless spark when switched on or off. In an ordinary household this is of no concern, but if a flammable atmosphere is present, the arc might start an explosion. In many industrial, commercial, and scientific settings, the presence of such an atmosphere is a common, or at least commonly possible, occurrence. Protecting against fire and explosion is of interest for both personnel safety as well as reliability reasons.
Several protection strategies exist. The simplest is to minimize the amount of electrical equipment installed in a hazardous location, either by keeping the equipment out of the area altogether, or by making the area less hazardous (for example, by process changes, or ventilation with clean air).
When equipment must be placed in a hazardous location, it can be designed to reduce the risk of fire or explosion. Intrinsic safety designs equipment to operate using minimal energy, insufficient to cause ignition. Explosion-proofing designs equipment to contain ignition hazards, prevent entry of hazardous substances, and, contain any fire or explosion that could occur.
Different countries have approached the standardization and testing of equipment for hazardous areas in different ways. Terminology for both hazards and protective measures can vary. Documentation requirements likewise vary. As world trade becomes more globalized, international standards are slowly converging, so that a wider range of acceptable techniques can be approved by national regulatory agencies.
The process of determining the type and size of hazardous locations is called classification. Classification of locations, testing and listing of equipment, and inspection of installation, is typically overseen by governmental bodies. For example, in the US by the Occupational Safety and Health Administration.
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In the US, the independent National Fire Protection Association (NFPA) publishes several relevant standards, and they are often adopted by government agencies. Guidance on assessment of hazards is given in NFPA 497 (explosive gas) and NFPA 499 (dust). The American Petroleum Institute publishes analogous standards in RP 500 and RP505.
NFPA 70, the National Electrical Code (NEC), defines area classification and installation principles.[1] NEC article 500 describes the NEC Division classification system, while articles 505 and 506 describe the NEC Zone classification system. The NEC Zone system was created to harmonize with IEC classification system, and therefore reduce the complexity of management.
Canada has a similar system with CSA Group standard C22.1, the Canadian Electrical Code, which defines area classification and installation principles. Two possible classifications are described, in Section 18 (Zones), and Appendix J (Divisions).
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A for use in mines, constructed so as not to cause external explosion of hazardous atmospheres. The heavy case is secured with tamper-resistant bolts to deter unauthorized opening of the case.The International Electrotechnical Commission publishes the series of standards[2] which defines a system for classification of locations, as well as categorizing and testing of equipment designed for use in hazardous locations, known as "Ex equipment". IEC -10-1 covers classification of explosive gas atmospheres, and IEC -10-2 explosive dust. Equipment is placed into protection level categories according to manufacture method and suitability for different situations. Unlike ATEX which uses numbers to define the safety "Category" of equipment (namely 1, 2, and 3), the IEC continued to utilise the method used for defining the safe levels of intrinsic safety namely "a" for zone 0, "b" for zone 1 and "c" for zone 2 and apply this Equipment Level of Protection to all equipment for use in hazardous areas since . <IEC .14>
The IEC standard set has been adapted for use in Australia and New Zealand and is published as the AS/NZS standard set.
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In an industrial plant, such as a refinery or chemical plant, handling of large quantities of flammable liquids and gases creates a risk of exposure. Coal mines, grain mills, elevators, and similar facilities likewise present the risk of a clouds of dust. In some cases, the hazardous atmosphere is present all the time, or for long periods. In other cases, the atmosphere is normally non-hazardous, but a dangerous concentration can be reasonably foreseen&#;such as operator error or equipment failure. Locations are thus classified by type and risk of release of gas, vapor, or dust. Various regulations use terms such as class, division, zone, and group to differentiate the various hazards.
Often an area classification plan view is provided to identify equipment ratings and installation techniques to be used for each classified area. The plan may contain the list of chemicals with their group and temperature rating. The classification process requires the participation of operations, maintenance, safety, electrical and instrumentation professionals; and the use of process diagrams, material flows, safety data sheets, and other pertinent documents. Area classification documentations are reviewed and updated to reflect process changes.
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Typical gas hazards are from hydrocarbon compounds, but hydrogen and ammonia are also common industrial gases that are flammable.
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An explosion of dust at this grain elevator in Kansas killed five workers inDust or other small particles suspended in air can explode.
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Class Division Description Class II Division 1 ignitable concentrations of combustible dust can exist, under normal conditions Division 2 ignitable concentrations of combustible dust are unlikely to exist normally Class III Division 1 ignitable fibers, or materials producing combustible flyings, are handled, manufactured or used Division 2 easily ignitable fibers are stored or handled Unclassified Non-hazardous or ordinary locations. Determined to be none of the above.[
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An old British standard used letters to designate zones. This has been replaced by a European numerical system, as set out in directive /92/EU implemented in the UK as the Dangerous Substances and Explosives Atmospheres Regulations .[3]
Zone Description Zone 20 ignitable concentrations of dust, fibers, or flyings are present for long periods of time Zone 21 ignitable concentrations of dust, fibers, or flyings are likely to exist under normal conditions Zone 22 ignitable concentrations of dust, fibers, or flyings unlikely to exist under normal conditions[
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Different explosive atmospheres have 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 (MESG), minimum igniting current (MIC) ratio, 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.[4]
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 vapor to form an ignitable mixture. The flash point determines if an area needs to be classified. A material may have a relatively low autoignition 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 for proper electrical system design, as it will then form an ignitable mixture.[5]
Each chemical gas or vapour used in industry is classified into a gas group.
NEC Division System gas & dust groups Area Group Representative materials Class I, Divisions 1 & 2 A Acetylene B Hydrogen C Ethylene D Propane, methane Class II, Divisions 1 & 2 E (Division 1 only) Metal dusts, such as magnesium (Division 1 only) F Carbonaceous dusts, such as carbon & charcoal G Non-conductive dusts, such as flour, grain, wood & plastic Class III, Divisions 1 & 2 None Ignitible fibers/flyings, such as cotton lint, flax & rayon NEC & IEC Zone System gas & dust groups Area Group Representative materials Zone 0, 1 & 2 IIC Acetylene & hydrogen(equivalent to NEC Class I, Groups A and B)
IIB+H2 Hydrogen(equivalent to NEC Class I, Group B)
IIB Ethylene(equivalent to NEC Class I, Group C)
IIA Propane(equivalent to NEC Class I, Group D)
Zone 20, 21 & 22 IIIC Conductive dusts, such as magnesium(equivalent to NEC Class II, Group E)
IIIB Non-conductive dusts, such as flour, grain, wood & plastic(equivalent to NEC Class II, Groups F and G)
IIIA Ignitible fibers or flyings, such as cotton lint, flax & rayon(equivalent to NEC Class III
Mines susceptible to firedamp I (IEC only) MethaneGroup IIC is the most severe zone system gas group. Hazards in this group gas 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 e II T4 then it is suitable for all subgroups IIA, IIB and IIC
A list must be drawn up of every explosive material that is on the refinery or chemical complex and included in the site plan of the classified areas. The above groups are formed in order of how explosive the material would be if it was ignited, with IIC being the most explosive zone system gas group and IIA being the least. The groups also indicate how much energy is required to ignite the material by energy or thermal effects, with IIA requiring the most energy and IIC the least for zone system gas groups.
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Equipment should be tested to ensure that it does not exceed 80%[according to whom?] of the autoignition temperature of the hazardous atmosphere. Both external and internal temperatures are taken into consideration. The autoignition temperature is the lowest temperature at which the substance will ignite without an additional heat or ignition source (at atmospheric pressure). This temperature is used for classification for industry and technology applications.[6]
The temperature classification on the electrical equipment label will be one of the following (in degree Celsius):
USA °C InternationalThe above table shows that the surface temperature of a piece of electrical equipment with a temperature classification of T3 will not rise above 200 °C. The surface of a high pressure steam pipe may be above the autoignition temperature of some fuel-air mixtures.
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Equipment can be designed or modified for safe operation in hazardous locations. The two general approaches are:
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Several techniques of flame-proofing exist, and they are often used in combination:
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Index
Ex code Description Standard Location Use Flame proof 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 μm) propane/ethylene, 0.004" (100 μm) acetylene/hydrogen)
IEC/EN -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 qualityEquipment can be installed in ANY housing provided to IP54.
A 'Zener Barrier', opto-isolator or galvanic unit may be used to assist with certification.
A special standard for instrumentation is IEC/EN &#;27, describing requirements for Fieldbus Intrinsically Safe Concept (FISCO) (zone 0, 1 or 2) (This special standard has been withdrawn, and has been partially replaced by: IEC/EN-11: and IEC/EN-25:)[1]
A special standard for instrumentation is IEC/EN &#;27, describing requirements for Fieldbus Non-Incendive Concept (FNICO) (zone 2) (This special standard has been withdrawn, and has been partially replaced by: IEC/EN-11: and IEC/EN-25:)[9]
IEC/EN -15The 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 the apparatus. These would be then labeled with each of the individual methods. For example, a socket outlet labeled EEx'de' might have a case made to EEx 'e' and switches that are made to EEx 'd'.
Equipment protection level (EPL)[
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In recent years also the 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 of protection I (mines) energized Ma II (gas) explosive atmosphere > hrs/yr 0 Ga ia, ma II (gas) explosive atmosphere between 10 and hrs/yr 1 Gb ib, mb, px, py, d, e, o, q, s II (gas) explosive atmosphere between 1 and 10 hrs/yr 2 Gc n, ic, pz III (dust) explosive surface > hrs/yr 20 Da ia III (dust) explosive surface between 10 and hrs/yr 21 Db ib III (dust) explosive surface between 1 and 10 hrs/yr 22 Dc ic[
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The equipment category indicates the level of protection offered by the equipment.
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In the US, the National Electrical Manufacturers Association (NEMA) defines standards for enclosure types for a variety of applications.[10][11] Some of these are specifically for hazardous locations:
NEMA Type Definition 7 Certified and labeled for use in indoor locations rated NEC Class I, Groups A, B, C, and D 8 Certified and labeled for use in locations rated NEC Class I, Groups A, B, C, and D; both indoors and outdoors 9 Certified and labeled for use in locations rated NEC Class II, Groups E, F, or G 10 Meets the requirements of the Mine Safety and Health Administration (MSHA), 30 CFR Part 18 ()[
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All equipment certified for use in hazardous areas must be labelled to show the type and level of protection applied.
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Mark for ATEX certified equipment for explosive atmospheresIn Europe the label must show the CE mark and the code number of the certifying/notified body). The CE mark is complemented with the Ex mark: A yellow-filled hexagon with the Greek letters εχ (epsilon chi), followed by the Group, Category, and, if Group II, G or D (gas or dust). Specific types of protection being used will also be marked.
Example markings Mark Meaning Ex II 1 G Explosion protected, Group 2, Category 1, Gas Ex ia IIC T4 Type ia, Group 2C gases, Temperature class 4 Ex nA II T3 X Type n, non-sparking, Group 2 gases, Temperature class 3, special conditions applyIndustrial electrical equipment for hazardous area has to conform to appropriate parts of standard: IEC- for gas hazards, and IEC- for dust hazards. In some cases, it must be certified as meeting that standard. Independent test houses&#;Notified Bodies&#;are established in most European countries, and a certificate from any of these will be accepted across the EU. In the United Kingdom, Sira and Baseefa are the most well known such bodies.
Australia and New Zealand use the same IEC- standards (adopted as AS/NZS ), however the CE mark is not required.
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In North America the suitability of equipment for the specific hazardous area must be tested by a Nationally Recognized Testing Laboratory, such as UL, FM Global, CSA Group, or Intertek (ETL).
The label will always list the class, division and may list the group and temperature code. Directly adjacent on the label one will find the mark of the listing agency.
Some manufacturers claim "suitability" or "built-to" hazardous areas in their technical literature, but in effect lack the testing agency's certification and thus unacceptable for the AHJ (Authority Having Jurisdiction) to permit operation of the electrical installation/system.
All equipment in Division 1 areas must have an approval label, but certain materials, such as rigid metallic conduit, does not have a specific label indicating the Cl./Div.1 suitability and their listing as approved method of installation in the NEC serves as the permission. Some equipment in Division 2 areas do not require a specific label, such as standard 3 phase induction motors that do not contain normally arcing components.
Also included in the marking are the manufacturers name or trademark and address, the apparatus type, name and serial number, year of manufacture and any special conditions of use. The NEMA enclosure rating or IP code may also be indicated, but it is usually independent of the Classified Area suitability.
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With the advent of electric power, electricity was introduced into coal mines for signaling, illumination, and motors. This was accompanied by electrically initiated explosions of flammable gas such as fire damp (methane) and suspended coal dust.
At least two British mine explosions were attributed to an electric bell signal system. In this system, two bare wires were run along the length of a drift, and any miner desiring to signal the surface would momentarily touch the wires to each other or bridge the wires with a metal tool. The inductance of the signal bell coils, combined with breaking of contacts by exposed metal surfaces, resulted in sparks, causing an explosion.[12]
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