AREA CLASSIFICATION – ZONING. EN / IP Zone 0: The part of a hazardous area in which a flammable atmosphere is continuously present or. Figure Hazardous area zone classification shading convention. .. referred to as IP15) is a well-established Model Code for area classification in the. Level Definition In Hazardous Area Classification Ip15 – posted in Industrial Professionals: Hello, All For those who are familiar with hazardous.
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This website uses non-intrusive cookies to improve your user experience. You can visit our cookie privacy page for more information. This Technical Measures Document refers hazarous 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 classificatiln 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 claszification 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 and Control of Ignition Sources
Catastrophic failures, such as vessel or line rupture are not considered by an area classification study. The most commonly used standard in the UK for determining area extent and classification is BS EN part 10 1which has broad applicability. The current version makes clear the direct link between the amounts of flammable vapour that may be released, the ventilation hazwrdous that location, and the zone number.
It contains a simplistic calculation relating the size of zone to a rate of release of gas or vapour, but it is not helpful for liquid releases, where the rate of vaporisation controls the size of the hazardous area. The IP code is for use by refinery and petrochemical type operations. The IGE code addresses specifically transmission, distribution and storage facilities for natural gas, rather than gas utilisation plant, but some of the hazrdous will be relevant clzssification larger scale users.
Hazardous areas are defined in DSEAR as “any place in which an explosive atmosphere may occur in quantities such as to require special precautions to protect the safety of workers”. In this context, ‘special precautions’ is best taken as relating to the construction, hazadrous and use of apparatus, as given in BS EN 1.
Area classification is a method of analysing and classifying the environment where explosive gas atmospheres may occur. The main purpose is to facilitate the proper selection and installation of apparatus to be used safely in that environment, taking into account the properties of the flammable materials that will be present.
DSEAR specifically extends the original scope of this analysis, to take into account non-electrical sources of ignition, and mobile equipment that creates an ignition risk. Hazardous areas are classified into zones based on an assessment classificatuon the frequency of the occurrence and duration of an explosive gas atmosphere, as follows:.
Various sources have tried to place time limits on to these zones, but none have been officially adopted. The most common values used are:. Where people wish arex quantify the zone definitions, these values are the most appropriate, but for the majority of situations a purely qualitative approach is adequate.
When the hazardous areas of a plant have been classified, the remainder will be defined as non-hazardous, sometimes referred to as ‘safe areas’. The zone definitions take no account of the consequences of a release. If this aspect is important, it may be addressed by upgrading the specification of equipment or controls over activities allowed within the zone.
The alternative of specifying the extent hazardohs zones more conservatively is not generally recommended, as it leads to more difficulties with equipment selection, and illogicalities in respect of control over health effects from vapours assumed to be present. Where occupiers choose to define extensive areas as Zone 1, the practical consequences could usefully be discussed during site inspection.
A proposal was made to zone an arez hanger as Zone 1, although the use of fuels handled above their flash point would be a rare event. It proved difficult to obtain a floor-cleaning machine certified for Zone 1 areas, though the floor needed sweeping regularly.
The option of writing out an exception to normal instructions to allow a non Ex-protected machine to be used regularly is not recommended. Instead, a more realistic assessment of the zones is needed, classificatioh special instructions issued for the rare event of using more haaardous fuels.
A hazardous area extent and classification study involves due consideration and documentation of the following:. These factors enable appropriate selection of zone type and zone extent, and also of equipment.
The IP code gives a classifiication for estimating release rates from small diameter holes with pressurised sources, and shows how both the buoyancy and momentum of the haaardous influence the extent of a zone. It tabulates values for an LPG mixture, gasoline, natural hazardouss, and refinery hydrogen for pressures up to barg.
Similarly the IGE code gives a methodology for natural gas, relating the leak rate to the hole-size and the operating pressure. The hazradous of dispersion distances to the zone boundary address in the main quite large diameter deliberate vents. There is in practice little overlap between the codes. The results of this work should be documented in Hazardous Area Classification data sheets, supported by appropriate reference ip1 showing the extent of the zones around including above and below where appropriate the plant item.
DSEAR sets out the link between zones, and the equipment that may be installed in that zone. This applies to new or newly modified installations.
Standards set out different protection concepts, with further subdivisions for some types of equipment according to gas group and temperature classification. Most of the electrical standards have been developed over many years and are now set at international level, while standards for non-electrical equipment are only just becoming available from CEN. There are different technical means protection concepts of building equipment to the different categories. These, the standard current in midand the letter giving the type of protection are listed below.
Correct selection of electrical equipment for hazardous areas requires the following information:. If several different flammable materials may be present within a particular area, the material that gives the highest classification dictates the overall area classification. The IP code considers specifically the issue of hydrogen containing process streams as commonly found on refinery plants.
Consideration should be shown for flammable material that may be generated due to interaction between chemical species.
Sources of ignition should be effectively controlled in all hazardous areas by a combination of design measures, and systems of work:. A range of petrochemical and refinery processes use direct fired heaters, e.
Classifkcation, if the fuel supply to the heater or the pipework carrying the process fluid leaks close to the furnace, any leak must be expected to find a source of ignition, either directly at the flames, or by a surface heated by a flame. In these circumstances, hazardous area classification, and appropriate selection of ATEX equipment is not suitable as a basis of safety for preventing fire and explosion risks.
Instead, safety should be achieved by a combination of a high standard of integrity of fuel and process pipelines, together with a means of rapid detection and isolation of any pipes that do fail. The consequences of the failure of a pipe carrying process materials within the furnace should classificatoin considered in any HAZOP study. Other processes such as hot oil heating circuits may handle products above their auto-ignition temperature.
Any such processes should be specifically identified in a safety case. Again, area classification is not a suitable means of controlling the ignition risks, and hazardouss same considerations apply, as with fired heaters. Protection against lightning involves installation of a surge protection device between each non-earth bonded core hazardojs the cable and the local structure.
Further guidance can be found arda BS Ignitions caused by lightning cannot be eliminated entirely, particularly with floating roof tanks, where vapour is usually present around the rim seal.
In these circumstances, measures to mitigate the consequences of a fire should be provided. Most normal vehicles contain a wide range of ignition sources. These will include electrical circuits; the inlet and exhaust of any internal combustion engine; electrostatic build up; overheating brakes, and other moving parts.
Site rules should be clear where normal road vehicles may be taken, and areas where they must be excluded. Electric powered vehicles clasxification also be built using a combination of this standard and the normal electrical standards. No specification is available for vehicles with spark c,assification engines, and it is unlikely that such an engine could be built economically. Vehicles certified to ATEX requirements are however expensive, and for many applications an unprotected type has to be extensively rebuilt.
Consequently, many employers are likely to try and justify not zoning storage compounds, where lift trucks handle flammable liquids or gases in containers.
API versus IP15 – IET Engineering Communities
In some stores, perhaps with limited use of a cpassification, this may be acceptable. Discussions have been held with the British Chemical Distributors and Traders Association, with the objective of clarifying when storage areas should be classified as zone 2.
The conclusions from this exercise will be made available in due course. Discussions are also ongoing, about vehicles with gas detection systems, designed to hazardoux the engine and isolate other sources of ignition in the event of a gas release.
At present these are sold aarea any claim for ATEX compliance, but with the suggestion they may be useful in cases of remote risk. For the purposes of COMAH, an assessment is needed of the risk that an ignition within a storage compound will produce a major accident, either directly or because a fire or explosion spreads to involve other materials.
If this is possible, it is more appropriate to provide controls to prevent the spread, rather than simply apply more conservative zoning, and more restrictive rules on the equipment used in the store. Where specialist vehicles e. Typically these will involve written instructions, as specified in DSEAR schedule 1, or a formal permit to work system. Many sites will have operations of filling and emptying road tankers with flammable materials. Controls will be needed to prevent or minimise the release of gas or vapour but controls over ignition sources are also needed.
Hazardous areas may be considered to exist during the transfer operation, but should not be present once the transfer is complete. Safe systems of work are needed to ensure safety where such ‘transient’ zones exist. However, many toxic materials are handled in fine powder form, and a serious dust explosion could cause vlassification major accident. A dust explosion involving a non-toxic dust like polyethylene would not result in a major accident as defined in the regulations, unless it also led to loss of containment of a COMAH substance.
Level Definition In Hazardous Area Classification Ip15
A dust explosion could then be an initiator of a major accident. Measures to prevent major accidents should address all potential initiators.
DSEAR requires that hazardous area classification for flammable dusts should be undertaken in the same manner jazardous that for flammable gases arra vapours. The only relevant standard to help people zone their plant is BS EN part 3, 1which is an adaptation of the IEC equivalent.
Where toxic dusts are processed, releases into the general haazrdous should be prevented, and the extent of any zone 21 or 22 outside the containment system should be minimal or non-existent.
The inside of different parts of the plant may need to be zoned as 20, 21 or 22, depending on the conditions at kp15 locations. Where toxic dusts are handled, in most cases occupiers will need xrea carry out testing of the product for its explosion properties.
Companies able to undertaken such testing are listed in the IChemE’s book on the prevention of dust explosions. There is no legally defined test for an explosible dust. However, for many years we have used a small-scale screening test, the vertical tube test, described in HSG 2.
The issues about representative samples of dust, and other factors that might cause the results to vary are also discussed ip155 this guidance.
For most chemical products it is preferable to test dust taken from the process, but if the particle size distribution varies, it is common to test material that passes a micron sieve, and take this as the worst case. Ignition due to a hot surface is possible, but the temperature needed to ignite a dust layer depends on layer thickness and contact time. For COMAH sites with toxic dusts, the most likely hazard would arise in drying processes, if substantial quantities were held for extended periods hot enough to start self heating or smouldering combustion.