Hazardous area classification in petroleum and chemical plants pdf
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- Hazardous Area Classification and Control of Ignition Sources
- Electrical equipment in hazardous areas
- Hazardous Area Classification in Petroleum and Chemical Plants: A Guide to Mitigating Risk
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Hazardous Area Classification and Control of Ignition Sources
Sources of such hazards include gases , vapors , dust , fibers, and flyings, which are combustible or flammable. Electrical equipment installed in such locations could provide an ignition source, due to electrical arcing , or high temperature. Standards and regulations exist to identify such locations, classify the hazards, and design equipment for safe use in such locations. 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. 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. 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. The International Electrotechnical Commission publishes the series of standards  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 covers classification of explosive gas atmospheres, and IEC explosive dust. 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.
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. Typical gas hazards are from hydrocarbon compounds, but hydrogen and ammonia are also common industrial gases that are flammable. Dust or other small particles suspended in air can explode.
An old British standard used letters to designate zones. 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.
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. Group IIC is the most severe Zone system gas group.
Hazards in this group gas can be ignited very easily indeed. 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. 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. The temperature classification on the electrical equipment label will be one of the following in degree Celsius :.
Equipment can be designed or modified for safe operation in hazardous locations. The two general approaches are:. Equipment has flameproof gaps max 0. A 'Zener Barrier', opto-isolator or galvanic unit may be used to assist with certification. 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. 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. The required Protection level is linked to the intended use in the zones described below:. All equipment certified for use in hazardous areas must be labelled to show the type and level of protection applied.
Specific types of protection being used will also be marked. Industrial 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. 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. 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. 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. 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. From Wikipedia, the free encyclopedia.
Electrical equipment in places where fire or explosion hazards may exist. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources.
Unsourced material may be challenged and removed. Main article: NEMA enclosure types. National Fire Protection Association. Retrieved UK Health and Safety Executive.
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Views Read Edit View history. Help Learn to edit Community portal Recent changes Upload file. Download as PDF Printable version. 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 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. Any arcs or sparks in this equipment has insufficient energy heat to ignite a vapour Equipment can be installed in ANY housing provided to IP Equipment is non-incendive or non-sparking.
This method, being by definition special, has no specific rules.
Electrical equipment in hazardous areas
James A. Huddleston, P. E lectrical and electronic equipment such as motors, generators, transformers, circuit breakers, fuses, switches, relays, solenoids and resistors produce significant amounts of heat, arcing and sparking during normal and abnormal operation, which could pose a substantial risk of fire or explosion in facilities where chemicals are manufactured, processed or utilized. This holds especially true for hazardous classified locations, i. H azardous area classification is the evaluation and classification of hazardous classified locations using scientific and engineering principles, within facilities where chemicals are manufactured, processed or utilized.
Beta This is a new way of showing guidance - your feedback will help us improve it. This Technical Measures Document refers to the classification of plant into hazardous areas, and the systematic identification and control of ignition sources. The relevant Level 2 Criteria are 5. The Dangerous Substances and Explosive Atmospheres Regulations DSEAR provide for the first time a specific legal requirement to carry out a hazardous area study, and document the conclusions, in the form of zones. Area classification may be carried out by direct analogy with typical installations described in established codes, or by more quantitative methods that require a more detailed knowledge of the plant. The starting point is to identify sources of release of flammable gas or vapour. These may arise from constant activities; from time to time in normal operation; or as the result of some unplanned event.
Hazardous Area Classification in Petroleum and Chemical Plants: A Guide to Mitigating Risk
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