Stray currents from electrical equipment Electrostatic discharge sparks: Lightning strikes. Electromagnetic radiation of different wavelengths Vehicles, unless specially designed or modified are likely to contain a range of potential ignition sources Sources of ignition should be effectively controlled in all hazardous areas by a combination of design measures, and systems of work: Using electrical equipment and instrumentation classified for the zone in which it is located. New mechanical equipment will need to be selected in the same way. 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.
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Stray currents from electrical equipment Electrostatic discharge sparks: Lightning strikes. Electromagnetic radiation of different wavelengths Vehicles, unless specially designed or modified are likely to contain a range of potential ignition sources Sources of ignition should be effectively controlled in all hazardous areas by a combination of design measures, and systems of work: Using electrical equipment and instrumentation classified for the zone in which it is located.
New mechanical equipment will need to be selected in the same way. 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.
Again, area classification is not a suitable means of controlling the ignition risks, and the same considerations apply, as with fired heaters. Lightning Protection 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. Vehicles 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. 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. Factors for Assessor of a Safety Case to Consider Is a full set of plans identifying hazardous areas available? For a large site they need not all be provided in the report, but those examples relevant to the representative set of major accidents upon which the ALARP demonstration is based must be included.
Have all flammable substances present have been considered during area classification, including raw materials, intermediates and by products, final product and effluents? Commonly these will be grouped for the purposes of any area classification study.
Locations where a large release is possible and the extent of hazardous areas has been minimised by the use of mechanical ventilation should be identified, e. Some reference to design codes, and commissioning checks to ensure the ventilation achieves the design aim, should be provided. The consequences of a loss of power to the system should be included in any section looking at other consequences of power loss.
Have appropriate standards been used for selection of equipment in hazardous areas? Existing plant will not meet the formula in DSEAR, but older standards distinguished between electrical equipment suitable for zones 0, 1 and 2.
Does the report identify old electrical equipment still in service in a hazardous area, and what assessment has been made to ensure it remains safe for use? Explosion prevention and protection. Basic concepts and methodology. Factors that could be considered during an on site inspection If there are any large areas of zone 1 on the drawings, is there evidence that by design and operation controls, the sources of release and consequently the location and extent of hazardous areas have been minimised?
Do any zone 2 areas extend to places where the occupier has inadequate control over activities that could create an ignition source, or is there any suggestion that the zone boundaries have been arbitrarily adjusted to avoid this? Has ignition protected electrical equipment been installed and maintained by suitably trained staff.
Are the risks from static discharges controlled properly? Earthing of plant, drums and tankers is the most basic requirement; other precautions are described in the references What control measures over ignition sources are adopted in hazardous areas during maintenance; where ignition sources must be introduced, typical precautions include the use of supplementary ventilation, portable gas detectors, and inerting of sections of plant. 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. Where toxic dusts are processed, releases into the general atmosphere 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 particular locations. The explosibility of dusts is dependent upon a number of factors: chemical composition; particle size; oxygen concentration; Where toxic dusts are handled, in most cases occupiers will need to carry out testing of the product for its explosion properties.
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 in 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. Status of Guidance Existing codes of practice provide information with respect to good practice for hazardous area classification. The standards detailing selection of appropriate electrical apparatus have been updated to take into consideration ventilation effects.
A list of ATEX harmonised standards can be checked on the EU web site : Equipment built to such a harmonised standard may assume automatic conformity with those essential safety requirements of relevant directives that are covered by the standard.
The EPS regulations describe the conformity assessment procedures that apply to different types of equipment. Appendix 3 describes the requirements for hazardous area classification. It suggests all drum stores should be zone 2, to a height 1m above the stack.
Discussions with industry on the relaxation of this in particular circumstances are ongoing. This contains very limited information on hazardous area classification or control of ignition sources HS G 2 Safe handling of combustible dusts: precautions against explosions, HSE, 2nd Edition, HS G 2 Lift trucks in potentially flammable atmospheres.
This is aimed mainly at small scale handling, with containers of litres or less. HS G 2 Formula for health and safety: guidance for small and medium sized firms in the chemical industry, HSE, The guidance describes the requirements for hazardous area classification, and gives some typical examples.
These should now be seen as rather conservative. This is basic level guidance, and COMAH reports should normally reference more specific publications, such as the other HSG series books listed, and other items in this list. Paragraphs 35 to 39 describe the requirements for hazardous area classification. Appendix 2 describes the requirements for hazardous area classification.
Contains useful information about electrostatic hazards during unloading. Part 1: Design, installation and operation of vessels located above ground, LP Gas Association, LPGA codes have not previously drawn a clear distinction between hazardous areas, and separation distances required for other reasons.
These are currently under revision, and will specify hazardous areas, that in most cases will be smaller than the separation distance. The guidance also recommends that zones be recorded in a plan to prevent sources of ignition being brought in. Equipment built to older standards, including purely national standards may remain in service, provided it is properly maintained. The IEC range of standards also includes documents on selection, installation and maintenance of equipment for use in explosive atmospheres.
Non-electrical equipment The first standard for explosion protected non-electrical equipment is BS EN part 1 1. It describes requirements for "Category 3" equipment. Further parts of this standard are well advanced and will appear during This gives additional general advice on the many of the issues covered in this TMD.
Electrostatic ignition risks The most recent general source of advice was drafted by a European standards working group, but was published in the UK as BS PD R and not as a full standard. It contains much useful advice about limiting pumping speeds, electrostatic risks from clothing, and many detailed operations. The two parts of the older BS 1 Code of Practice for the control of undesirable static electricity remain current, because they contain some useful information not duplicated by the PD.
The different parts of this standard set out requirements for construction of equipment for use in atmospheres containing explosive dusts; information about selection and maintenance; and BS EN 1 covers the classification of areas where combustible dusts are or may be present. BS 1. Code of practice for protection of structures against lightning, British Standards Institution. Section 9 provides guidance on lightning protection of structures with inherent explosive risks.
Lightning protection. Section 23 provides guidance on lightning protection.
Area Classification to Ip 15
Risk assessment , Leadership EI Model code of safe practice Part Area classification code for installations handling flammable fluids commonly known as EI 15 is recognised internationally as being the de-facto guidance for calculating hazardous zone areas in the petroleum industry. It is essential for HSE managers, design, process and maintenance engineers, and all those involved in the hazardous area classification of installations handling flammable fluids. It provides a demonstrable methodology for determining hazard radii, and is applicable to all installations handling flammable fluids. It gives guidance on the classification of regions around equipment handling or storing flammable fluids, and provides a basis for both the correct selection of fixed electrical equipment and the location of other fixed sources of ignition in those areas.
Hazardous Area Classification and Control of Ignition Sources
Codes and. Zone 0. Zone 1. Zone 2. IEC , IP 15,. Division 1. Division 2.