A characterization of T3 separation for a special class of varieties

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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, and special instructions issued for the rare event of using more volatile 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 methodology for estimating release rates from small diameter holes with pressurised sources, and shows how both the buoyancy and momentum of the release influence the extent of a zone. It tabulates values for an LPG mixture, gasoline, natural gas, 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 tables 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 drawings 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 mid , and the letter giving the type of protection are listed below.

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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. Clearly, 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 be 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.

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Again, area classification is not a suitable means of controlling the ignition risks, and the same considerations apply, as with fired heaters. Protection against lightning involves installation of a surge protection device between each non-earth bonded core of the cable and the local structure. Further guidance can be found in BS 1 - Code of practice for protection of structures against lightning.

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 can also be built using a combination of this standard and the normal electrical standards. No specification is available for vehicles with spark ignition 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.

In some stores, perhaps with limited use of a vehicle, 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 shut the engine and isolate other sources of ignition in the event of a gas release.

At present these are sold without 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.

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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 a 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.

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 as that for flammable gases and vapours. Any array with a compatible base type can be passed to an openarray parameter, the index type does not matter.

In addition to arrays sequences can also be passed to an open array parameter. The openarray type cannot be nested: multidimensional openarrays are not supported because this is seldom needed and cannot be done efficiently.

  1. Hazardous Area Classification and Control of Ignition Sources!
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  6. A varargs parameter is an openarray parameter that additionally allows to pass a variable number of arguments to a procedure. The compiler converts the list of arguments to an array implicitly:. This transformation is only done if the varargs parameter is the last parameter in the procedure header. It is also possible to perform type conversions in this context:. Note that an explicit array constructor passed to a varargs parameter is not wrapped in another implicit array construction:.

    This is required so that the builtin echo proc does what is expected:. The UncheckedArray[T] type is a special kind of array where its bounds are not checked. This is often useful to implement customized flexibly sized arrays.

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    Additionally an unchecked array is translated into a C array of undetermined size:. The base type of the unchecked array may not contain any GC'ed memory but this is currently not checked.

    Future directions : GC'ed memory should be allowed in unchecked arrays and there should be an explicit annotation of how the GC is to determine the runtime size of the array. A variable of a tuple or object type is a heterogeneous storage container. A tuple or object defines various named fields of a type. A tuple also defines an order of the fields.