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Operation Of Electrical Equipment In Hazardous Environment Environmental Sciences Essay

Based on my research up to day of the month I came to the decision that risky countries is a large subject to cover and after a series of meetings with my supervisor Mr. Jerry Duggan I have decided to concentrate preponderantly on “ Dust Explosion ” a subject which has ne’er been covered before by an electrical technology pupil in Cork Institute of Technology.

By finishing this undertaking my purpose is that it will function as an educational tool in our progressive environment for me and for future readers.

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I hope to larn many things from this undertaking that will profit me in the hereafter and in my calling. I intend to analyze all the of import facets of dust detonation, by reexamining bing literature on the topic, hunt of appropriate web sites and by a possible site visit to a chemical works near me.

1 Introduction:

In Electrical technology, a risky location is defined as a topographic point where concentrations of flammable gases, bluess, or dusts may happen. Electrical equipment that must be installed in such locations is particularly designed and tested to guarantee it does non get down an detonation, due to curving contacts or high surface temperature of equipment.

For illustration a family light switch may breathe a little, harmless seeable flicker when shift ; in an ordinary ambiance this discharge is if no concern, but if a flammable vapor was present, the discharge might get down an detonation. Electrical equipment intended for usage in a chemical mill or refinery is designed non to bring forth any flickers, or else to safely incorporate the discharge and do certain it can non light any explosive gases, bluess or dusts that might be present around the equipment.

Many schemes exist for safety in electrical installings. The simplest scheme is to minimise the sum of electrical equipment installed in a risky country, either by maintaining the equipment out of the country wholly or by doing the country less risky by procedure betterments or airing with clean air. Intrinsic safety is a pattern where setup is designed with low power degrees and low stored energy, so that a mistake is improbable to put off an detonation. Equipment enclosures can be pressurized with clean air, and interlocked so that the equipment is disconnected if the air supply fails or arc-producing elements of the equipment can be isolated from the environing atmosphere by encapsulation, submergence in oil, sand, or by hardy enclosures that prevent extension of an internal detonation to the environing ambiance.

As in most Fieldss of electro engineering, different states have approached the standardisation and testing of equipment for risky countries in different ways. As universe trade becomes more of import in distribution of electrical merchandises, international criterions are easy meeting so that a wider scope of acceptable techniques can be approved by national regulative bureaus.

Standards regulating electrical equipment for usage in risky dust countries are altering so quickly that purchasers and users of electrical production equipment are happening it hard to maintain up. However, A by non maintaining abreast of the alterations, they run the hazard of a dust detonation happening in their works due to inadequately protected equipment and/or being prosecuted forA non-compliance or carelessness.

The hazard of a dust or pulverization detonation happening in a fabrication works should non be underestimated. Around 2,000 dust detonations occur in Europe every twelvemonth, impacting all types of companies, including makers of sugar, coal, chocolate, flour-based goods, milk pulverization, tea, grain, fresh fish and baccy, every bit good as wood and metal processing companies.

Any environment in which dust or pulverization is allowed to garner on hot surfaces or that could be ignited by a flicker from electrical equipment is a possible hazard. The cost, in footings of lives lost and harm to works, as a consequence of a dust detonation can be tremendous.

2 Dust Explosion:


Dust detonations occur when all right atoms dispersed in the air as a cloud react with O in the presence of an ignition beginning, bring forthing an detonation concatenation reaction. When this occurs in a changeless volume, there is a rapid and important addition in force per unit area.

Prevention steps must be the first line of defense mechanism against such detonations, but in many state of affairss efforts to extinguish ignition beginnings are merely non plenty. Measures for extenuating the harm caused and the dangers posed to workers by eventual detonations are necessary. To assist vouch the safety of silo installings, companies in Europe are required to follow with the ATEX Directives sing explosive ambiances ( [ ATEX 1999/92/EC, 1999 ] and [ ATEX 94/9/EC, 1994 ] ) by put ining protection mechanisms.

3 What is a dust detonation?

Explosions are defined as sudden reactions affecting a rapid physical or chemical oxidization reaction, or disintegrate bring forthing an addition in temperature or force per unit area, or both at the same time. When the fire velocity is greater than the velocity of sound, we call it a explosion. Otherwise the detonation is known as a deflagration. Typically, dust detonations are comparatively slow burning procedures. If ignition occurs in a dust cloud in an unfastened country, so small or no overpressure consequences and the primary jeopardy is a bolide. The best manner to acquire informations refering a specific type of dust is to make proving on the existent substance. Most written proficient resources on dust detonations have informations for the minimal explosive concentrations and other belongingss of common pulverizations.

4 European Laws:

In July 2006 a 2nd ATEX directive became compulsory European Standard EN 14491, 2006 EN 14491 for dust detonation venting protective systems and CEN ( 2006 ) .EN 14491 ( 2006 ) for the discharge of dust detonations came into force in 2006 and depict the basic design demands for dust detonation venting systems. This criterion is one of a series including criterions EN 14797 ( 2006 ) and EN 14460 ( 2006 ) on blowhole industry and detonation immune constructions. Together, these three criterions wholly cover dust detonation venting ordinances in Europe.

5 Conditionss for dust detonation:

As we all know detonation can merely happen, when three factors come together:

1. Flammable stuff ( in burnable measures )

2. Oxygen ( in the air )

3. Ignition beginning

Fig.1 An detonation can merely happen, when these three factors come together

Once the reaction is ignited, depending on how the exothermal energy is liberated, the consequences can be a controlled burning, fire moving ridge or detonation.

All the protection methodological analysiss are seeking to extinguish one or more of the trigon constituents to cut down the hazard of lighting an detonation to an acceptable degree. To obtain an acceptable degree of hazard at least two independent events must be present, each one of low chance, before a possible detonation can happen.

There are besides five necessary conditions for dust detonation to happen:

a dust has to be combustible

the dust is suspended in the air at a high concentration

there is an oxidizer ( typically atmospheric O )

the dust is confined

there is an ignition beginning

Fig.2 Necessary conditions for dust detonation to happen

The add-on of the two elements scattering and parturiency to the trigon ( see fig.1 ) creates what is known as the “ detonation Pentagon ” ( see fig. 2 ) .

An initial primary detonation ( see fig. 3 ) in treating equipment or in an country were fleeting dust has accumulated may agitate free more accrued dust or damage a containment system such as a canal, vas or aggregator. As a consequence, if ignited, the extra dust dispersed into the air may do one or more secondary detonations ( see fig. 3 ) . These can be far more destructive than a primary detonation due to increased measure and concentration of spread combustible dust.

Fig. 3 Primary and secondary dust detonations

If one of the elements of the detonation Pentagon is losing, a ruinous detonation can non happen. Two of the elements in the detonation Pentagon are hard to extinguish: O ( within air ) , and parturiency of the dust cloud ( within procedures or edifices ) . However, the other three elements of the Pentagon can be controlled to a important extent, and will be discussed farther in this papers.

6 Facility Dust Hazard Appraisal:

As I have mentioned above a combustible dust detonation jeopardy may be in a assortment of industries, including: nutrient ( e.g. , confect, amylum, flour, provender ) , plastics, wood, gum elastic, furniture, fabrics, pesticides, pharmaceuticals, dyes, coal, metals ( e.g. , aluminum, Cr, Fe, Mg, and Zn ) , and fossil fuel power coevals. The huge bulk of natural and man-made organic stuffs, every bit good as some metals, can organize combustible dust. The European`s Industrial Fire Hazards Handbook

provinces that “ any industrial procedure that reduces a combustible stuff and some usually non-combustible stuffs to a finely divided province nowadayss a possible for a serious fire or detonation. ”

7 Facility Analysis Components:

Facilities should carefully place the followers in order to measure their possible for dust detonations:

Materials that can be combustible when finely divided ;

Procedures which use, consume, or produce combustible dusts ;

Open countries where combustible dusts may construct up ;

Hidden countries where combustible dusts may roll up ;

Meanss by which dust may be dispersed in the air ; and

Potential ignition beginnings.

8 Beginnings of ignition:

There are many beginnings of ignition and a bare fire need non be the lone one, a study shows that half of the dust detonations in Europe were from non-flame beginnings. Beginnings include


hot surfaces


curving from machinery or other equipment

illuming work stoppages

cutting and welding fires

mechanical machinery

As I mentioned earlier at the start of the study a differentiation is made between primary and secondary dust detonations. When a dust is found in a container, room or system component ignites and explodes we speak of a primary dust detonation. In a secondary dust detonation, dust that has settled on the land or on other surfaces is stirred by the primary detonation and ignites. As a consequence of this a concatenation reaction follows and the force per unit area wave emanating from the secondary dust detonation can stir up farther dust sedimentations and do farther dust detonations.

9 Example of Historic Incidents:

The undermentioned incident is an incident that marked the universe, in February 2008, a ruinous dust detonation occurred at the Imperial Sugar Refinery in Port Wentworth, USA. The dust detonation killed 13 people and injured many more.

The undermentioned images below show the amendss of the refinery after the catastrophe ;

10 Measuring the hazard:

Identifying risky or non-hazardous countries should be carried out in a systematic manner. Risk appraisal should be used to find if risky countries exist and to so delegate zones to those countries.

The appraisal should see such affairs as:

the risky belongingss of the unsafe substances involved ;

the sum of unsafe substances involved ;

the work processes, and their interactions, including any cleansing, fix or care activities that will be carried out ;

the temperatures and force per unit areas at which the unsafe substances will be handled ;

the containment system and controls provided to forestall liquids, gases, bluess or dusts get awaying into the general ambiance of the workplace ;

any explosive ambiance formed within an enclosed works or storage vas ; and,

any steps provided to guarantee that any explosive ambiance does non prevail for an drawn-out clip, e.g. airing.

Taken together these factors are the get downing point for risky country categorization, and should let for the designation of any zoned countries. The undermentioned paragraphs give farther information on what to see during an appraisal.

11 The risky belongingss of unsafe substances:

The belongingss of a unsafe substance that need to be known include the boiling point and brassy point of any flammable liquid, and whether any flammable gas or vapor that may be evolved is lighter or heavier than air. For dusts, information on atom size and denseness will be needed, one time it has been shown that a peculiar dust can organize an explosive ambiance. Often, relevant information is contained on a safety informations sheet provided with the merchandise.

12 The size of possible releases:

Some possible beginnings of release may be so little that there is no demand to stipulate a risky country. This will be the instance if the effect of an ignition following a release is improbable to do danger to people in the locality. However, in the incorrect fortunes ignition of rather little measures of flammable gas/vapour assorted with air can do danger to anyone in the immediate locality. Where this is the instance, as in a comparatively confined location, from which rapid flight would be hard, country categorization may be needed even where rather little measures of unsafe substance are present.

The size of any possible explosive ambiance is, in portion, related to the sum of unsafe substances present. Industry specific codifications have been published by a assortment of organisations to supply counsel on the measures of assorted unsafe substances that should be stored. For illustration,

13 Temperatures and force per unit areas:

Extra information associating to the procedure that involve the unsafe substances should besides be taken into history, including the temperatures and force per unit areas used in the procedure, as this will act upon the nature and extent of any release, and the extent of any subsequent risky countries. Some substances do non organize explosive ambiances unless they are heated, and some liquids if released under force per unit area will organize a all right mist that can detonate even if there is deficient vapor.

14 Ventilation:

Ventilation, either natural, or automatically ( e.g. produced by fans ) , can both dilute beginnings of release, and take unsafe substances from an enclosed country. As a consequence there is a close nexus between the airing at any given location and the categorization and extent of a zone around a possible beginning of release. Well designed airing may forestall the demand for any zoned country, or cut down it so it has a negligible extent.

15 Extent of risky countries:

The appraisal needs to place countries within a workplace that are connected to topographic points where an explosive ambiance may happen. This will supply information on any countries off from the beginning of the jeopardy to which an explosive ambiance may distribute, for illustration through canals. Such countries should be included in the categorization system for topographic points where explosive ambiances may happen. An attack to measuring this hazard is described in BS EN 60079/10. A technique for forestalling this hazard is described in BS EN 50016, on pressurisation of enclosures or suites incorporating electrical equipment.

16 Other considerations:

When sing the potency for explosive ambiances, it is of import to see all unsafe substances that may be present at the workplace, including waste merchandises, residues, stuffs used for cleansing or care, and any used merely as a fuel. Besides some combinations of unsafe substances may respond together, organizing an ignition beginning, or in combination may organize an explosive ambiance, where singly this does non happen.

Some perennial activities such as refuelling autos, or lading and droping oilers intended for usage on the public roads, involve the debut of possible beginnings of ignition into an country where a spill is possible, and which would run into the description of a risky country. In these fortunes, safety can be achieved by insulating power beginnings ( e.g. turning off engines, etc ) while a transportation is taking topographic point, and doing suited cheques before and after a transportation, before traveling a vehicle into or out of a risky country.

Activities, such as care, may incur hazards non covered by the normal country categorization of the country where the activity is taking topographic point, for case the debut of beginnings of ignition into a risky country. Sometimes the unsafe substance can be removed before the care work activity starts. Sometimes, particular control steps can be taken to forestall the release of any unsafe substance during the work. In such instances the extra hazards associated with the activity should be assessed before work starts.

17 Relationship between fires and detonations:

In many instances where an explosive ambiance can organize, any ignition will do a fire instead than an detonation. Both fire and detonation cause dangers to workers, and in many instances the safeguards required to forestall an ignition are the same. The overall bundle of safeguards required will depend on the possible effects of a fire or detonation.

Many factors influence the hazards from a fire affecting unsafe substances.

In peculiar, employers should see whether a fire could take to an detonation, how fast a fire might turn, what other stuffs might be quickly involved, any dangers from fume and toxic gases given off, and whether those in the locality would be able to get away.

18 Classifying risky countries into zones:

Once an country has been identified as risky it should be classified into zones based on the frequence and continuity of the potentially explosive ambiance. This so determines the controls needed on possible beginnings of ignition that may be present or happen in that country. These controls apply peculiarly to the choice of fixed equipment that can make an ignition hazard ; but the same rules may be extended to command the usage of nomadic equipment and other beginnings of ignition that may be introduced into the country ( for illustration, lucifers and igniters ) and the hazards from electrostatic discharges.

An international criterion, BS EN 60079/10, explains the basic rules of country categorization for gases and bluess, and its equivalent for dusts was published in 2002 as BS EN 61241/3. These criterions form a suited footing for measuring the extent and type of zone, and can be used as a usher to following with the demands in DSEAR. However, they can non give the extent and type of zone in any peculiar instance, as site-specific factors should ever be taken into history.

Industry specific codifications have besides been published by assorted administrations and, provided they are applied suitably, they are valuable in promoting a consistent reading of the demands.

Area categorization surveies normally take the signifier of drawings placing the risky countries and zones. Additional text gives information about the unsafe substances that will be present, the work activities that have been considered, and other premises made by the survey. Whenever such drawings and paperss have been produced, they should be included in the hazard appraisal record required by DSEAR. These paperss should be considered whenever new equipment is to be introduced into a zoned country.

Hazardous topographic points are classified in footings of zones on the footing of the frequence and continuance of the happening of an explosive ambiance.

Gass, bluess and mists

For gases, bluess and mists the zone categorizations are:

Zone 0 – can be describes as a topographic point in which an explosive ambiance dwelling of a mixture with air of unsafe substances in the signifier of gas, vapor or mist is present continuously or for long periods or often.

Zone 1 – can be described as a topographic point in which an explosive ambiance dwelling of a mixture with air of unsafe substances in the signifier of gas, vapor or mist is likely to happen in normal operation on occasion.

Zone 2 – can be describes as a topographic point in which an explosive ambiance dwelling of a mixture with air of unsafe substances in the signifier of gas, vapor or mist is non likely to happen in normal operation but, if it does happen, will prevail for a short period merely.


For dusts the zone categorizations are:

Zone 20 – can be describes as a topographic point in which an explosive ambiance in the signifier of a cloud of combustible dust in air is present continuously, or for long periods or often.

Zone 21- can be describes as a topographic point in which an explosive ambiance in the signifier of a cloud of combustible dust in air is likely to happen in normal operation on occasion.

Zone 22 -can be describes as a topographic point in which an explosive ambiance in the signifier of a cloud of combustible dust in air is non likely to happen in normal operation but, if it does happen, will prevail for a short period merely.

19 Equipment in risky countries:

Particular safeguards need to be taken in risky countries to forestall equipment from being a beginning of ignition. In state of affairss where an explosive ambiance has a high likeliness of happening, trust is placed on utilizing equipment with a low chance of making a beginning of ignition. Where the likeliness of an explosive ambiance happening is reduced, equipment constructed to a less strict criterion may be used. Equipment is categorised ( 1, 2 or 3 ) depending on the degree of zone where it is intended to be used. A figure of ways of building equipment to forestall ignition hazards have been published as consonant European Standards, and in some instances, extra demands are set out in the Standards associating to installing and usage.

The risky country zone categorization and corresponding equipment classs are:

Zone 0 or zone 20 – class 1 equipment

Zone 1 or zone 21 – class 2 equipment

Zone 2 or zone 22 – class 3 equipment

20 Marking of equipment:

A standardized marker strategy is applied to place equipment suited for a specific location. Equipment built will transport the detonation protection symbol “ Ex ” in a hexagon, the equipment class figure ( 1, 2, or 3 ) , the missive G and/or D depending on whether it is intended for usage in gas or dust ambiances, and other indispensable safety information. In many instances this will include a temperature evaluation expressed as a “ T ” marker, and sometimes a gas group. These indicate restrictions to safe usage. Employers and those installing equipment should see the marker and certification provided with “ Ex ” equipment when it is being installed.

All ATEX equipment will be required to transport three Markss.

The CE grade

The ATEX grade

The Certification Code

Additionally, it must be marked decipherably with the following minimal specifics:

Name and reference of maker

Appellation of series/type/model

Consecutive figure

Year of industry

The CE Mark:

All ATEX equipment must transport CE grade ; the minimal tallness is 5mm.

The CE grade confirms conformity with all the comparative Directives.

The ATEX Mark:

The ATEX grade ( EU Explosive Atmosphere symbol ) is a bluish hexagon incorporating the conventionalized letters Ex

The Certification Code:

All equipment points are required to transport the Certification Code as portion of their designation label.

Log Table:

Date 9/11/2009 I met up Mr. Jerry Duggan and discussed the importance of this undertaking and what country of jeopardies am I interested in to cover my undertaking.

Date 11/11/2009 In my ain clip I got to seek the webs and happen out what is a dust detonation and what universe and European Torahs are out at that place to forestall these detonation from go oning and if they do go on due to unknown fortunes, how to carry on an detonation appraisal.

Date 14/11/2009 I did some book research and reading from what was available in the library and what Mr. Jerry Duggan gave me and go really familiar with the factors that can take to an detonation. The book entitled “ Electrical Apparatus and Hazardous Areas ” became really ready to hand to understand the different zones for gas and blues, and dust jeopardies.

Date 17/11/2009 After farther research in jeopardies I have decided to concentrate merely on one country preponderantly “ dust detonation ” . The meeting helped me understand how to near this country, which non many people know excessively much about.

Date 19/11/2009 While making some internet research I came across a papers saying that half of the dust detonations go oning in Europe were from non-flammable beginnings. The beginnings that could take to an ignition were stated and an incident illustration was given.

Date 21/11/2009 As a consequence of including an illustration of dust detonation that took topographic point in the USA, I wanted to show a hazard appraisal in order to find if risky countries exist in an enclosed country and so to delegate zones to those countries.

Date 23/11/2009 I showed Mr. Jerry Duggan my up to day of the month research on dust detonation and advised me to seek and acquire a site visit which will profit me better on my stage research and the completion of the study.

Date 24/11/2009 On this twenty-four hours I researched how would ventilation either of course or automatically ( produced by fans ) can both seek and extinguish beginnings of release and most of import take the unsafe substances from an enclosed country.

Date 27/11/2009 Leaving unprecedented work unfinished from the day of the month of 14/11/2009 I wanted to lucubrate more on the designation of a hazard topographic point and the categorization into zones. Research had to be done to happen a definition on the zones categorization for dust.

Date 30/11/2009 After farther desk research I met up once more and discussed the layout of my concluding twelvemonth presentation and a day of the month was set on the 10/12/2009 along with my assessor.

Table of figures:

The undermentioned figures are listed below as they appear in the study:

Figure 1: An detonation can merely happen, when one of this factors come together

Figure 2: Necessary conditions for dust detonation to happen

Figure 3: Primary and secondary dust detonations


Electrical Apparatus and Hazardous Areas/Fifth Edition by Robin Garside

Electrical Installation in Hazardous Areas by Alan McMillan

Introduction to Intrinsic Safety

Links & A ; Mentions:

HBIRDPRO- # 692251-HOT Work

HBIRDPRO- # 570000-Safety Signs

HBIRDPRO- # 562514-Welding

Thymine: TemplatesOH & A ; S – Occupational Health & A ; SafetyPTW Hot Work Control Guide.dot

Thymine: TemplatesOH & A ; S – Occupational Health & A ; SafetyATW Hot Work Control Guide.dot

OH & A ; S – Occupational Health & A ; SafetyHazardous Area Check Sheet Equipment In Combustibles Dust Areas



Corporate Standard Hazardous Areas

Handbook for risky country solution No. 14 – AB – Iraqi national congress

A cosmopolitan attack for hazardous-area categorizations

A usher to European ( EEC ) enfranchisement for electrical equipment in risky countries

DOE Handbook Electrical Safety 1998

Web sites: