ELECTRICAL

Presentation by

SUSANTA KUMAR ALLEY

(Retd) Dy General Manager, SAIL, BSL

Member NSCI, FSAI, AEI

Visiting Faculty on Industrial Safety

Lead Auditor OHSAS -18001:2007

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TERMINOLOGY

HAZARD – A physical situation with potential for human injury,damage to property, damage to the environment or some combinationof these

HAZARD IDENTIFICATION – The process of examining each workHAZARD IDENTIFICATION – The process of examining each workarea and work task for the purpose of identifying all the hazards whichare ‘inherent in the job’. It may include examining men who work,machine on which the work is done, material & tool that are used andmethod of work (in operation & maintenance ) which is applied. It mayalso identify sources of process accidents involving release ofhazardous material in the atmosphere and various ways they couldoccur.

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TERMINOLOGY

RISK – The likelihood of an undesired event with specifiedconsequence occurring within a specified period or in specifiedcircumstances.

RISK ASSESSMENT – It is defined as the process of assessing theRISK ASSESSMENT – It is defined as the process of assessing theeconomical loss, human injury or environmental damage both in termsof likelihood and magnitude of loss, injury or damage. Risk isexpressed as a product of frequency of an event and the magnitude ofthe consequences that result each time the event occurs.

Risk score = frequency x consequence

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WHY HAZARD IDENTIFICATION?

Electricity is a widely used, efficient and convenient, but potentially hazardousmethod of transmitting and using energy.

Electric power is used in houses, factories, public places and commercialestablishments etc. for lighting, operating appliances & machines, heating,cooling, chemical process and transport

Working with electricity is one of the most dangerous jobs in an industry with

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Working with electricity is one of the most dangerous jobs in an industry withnumber of accidents including deaths

People tend to be careless while handling electrical equipment & appliances,may cause irreparable loss to life and property,

Proper controls & precautions will render its use a safe.

Safety precautions must be taken at every stage of work i.e. design,manufacturing, installation, testing & commissioning, operation andmaintenance.

Safety precautions should be documented in the form of Do’s & Don’ts.Warning signs must be displayed.

WHO IS EXPOSED?

Person touching non-effectively earthed, faulted metal parts inelectrical installation

Person who are unaware of presence of electrical power and areworking in vicinity of live parts like:

1. Construction workers - not qualified & knowledgeable yet employed tohandle & use electrical system and applianceshandle & use electrical system and appliances

2. Electrical machine operator – handling, operating, maintaining equipment,appliances, devices

3. Persons - in switchyard, substation, electrical maintenance of residentialbuildings

4. Innocent persons who work in the danger zone

5. Regular electrical employee tending to be over-confidant & negligent

6. Person exposed to danger due to ‘mistake of others ‘ or ‘faulty equipment’

Rules & Regulations provide guidelines to employers on who should be engaged on electrical works

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HAZARDS IN ELECTRICITY Primary Hazards

• Electric Shock – A person becomes a part of an electric circuit.(Current passes through the body in a variety of situation)

• Fire and Explosion – Unprotected circuit elements areoverloaded, Ignition temperature of the materials adjacent to

6

• Fire and Explosion – Unprotected circuit elements areoverloaded, Ignition temperature of the materials adjacent toor in contact of the hot surface is reached

• Joule’s Burn – Electric current passing thro’ body or a arc flashmay cause electrical burn

• Arc Flash & Arc blast – The dangerous event can causetemperatures to rise as high as 350000 F It can cause injury tounprotected workers many feet away from arc flash

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DANGERS OF ELECTRICAL SHOCKThere is always a chance of electrocution , even in dry condition

If you are in contact with a live wire orany component of an energized electdevice and also in contact with groundedobject you will receive shock.

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object you will receive shock.Plumbing is often grounded. Metalelectrical boxes and conduit are groundedRisk of receiving shock is more if youstand on a puddle of water. Wet clothing,high humidity, and perspiration increasechances of electrocution, even in drycondition.

OCCURRENCE OF ELECTRIC SHOCK“A sudden stimulation of nervous system of human body by flow of current thro’ a part of body. A life-

threatening situation”

Human body gets electric shock when current flows thro’ any part of the body due to applied voltage across that part

Current flows through body: When part of human body bridges two phase wires by direct contact

When part of human body bridges 1ph and earth, 2 ph & earth directly When part of human body bridges 1ph and earth, 2 ph & earth directly

When part of human body touches 2 points at different potential

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OCCURRENCE OF ELECTRIC SHOCK“A Live conductor does not differ in appearance from a Dead conductor”

Shocks from 3-phase a,c. System

Statistics show that the number of electrical accidents usually constitutes 8%(max) to total number of accidents in an industry. The % of elect accidents thatprove fatal are 40% of fatalities taken as a whole. There are evidences that mostaccidents occur on MV or LV systems.

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OCCURRENCE OF ELECTRIC SHOCK

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HAZARDS IN ELECTRICITYSecondary Hazards

Fall from heightFall of hand held working toolsDirect burn from electric arc welding – 23000 CU/V & Infra-red Radiation burns to eyes from arc welding

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to eyes from arc weldingEye injury from electric arcs (e.g. Welder’s eye flash)Physical injury from false starting of machine, Explosion of switch gears etc (Never face it while making it ‘ON’)

A CASE STUDY

A maintenance man rode 12’ above the floor level to work on a 240V lightfixture. He did not turn off the power supply to the lights. He removed the linefuse from the ‘black’ wire, which he thought was the hot wire. The black wirewas ‘neutral’ and the ‘Red’ wire was the live wire. He began to strip the redwire using a wire striper in his right hand. Electricity passed from the live redwire to the striper, then into his right hand and through his body, and then towire to the striper, then into his right hand and through his body, and then tothe ground through his left index finger. A co-worker heard a noise and sawthe victim lying face-up on the lift. He summoned other workers, who loweredthe platform and performed ‘CPR’ but the victim could not be saved.

To prevent injuries and deaths we must remember the following:

Test the circuit and make sure that it is de-energized

Never attempt to handle any wire/conductor until you are absolutelysure that the wire is not ‘live’. Always assume a conductor is dangerous

Be sure to lock-out and tag-out circuits so that they cannot be re-energized

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SEVERITY OF ELECTRICAL SHOCKS“Passage of a.c current of 1mA thro’ human body is safe for an unlimited time: 65mA can be safe for 1.0 sec;

and 500mA for 0.1 sec”

For children the current valuesare half of corresponding valuesof men

When current >16mA passes thro’forearm, involuntary contractionof muscles occur, victim may be

Magnitude of CurrentMagnitude of Current

50Hz, rms value50Hz, rms value

EffectEffect

<10mA<10mA “Let“Let--gogo--current”, Mild current”, Mild

sensation, not painfulsensation, not painful

10mA 10mA –– 15mA15mA “Let“Let-- nono-- go go --current”, Painful current”, Painful

shock, muscle still in controlshock, muscle still in controlof muscles occur, victim may beunable to release the energizedobject he grasps

If heart is feebly beating and flowof shock current is stopped, theprocess may get reversed &regular heart beat and breathingmay resume. This reversal ishelped by “Artificial Respiration”

15mA 15mA –– 20mA20mA Muscle control affected, Muscle control affected,

Paralysis of respiratory Paralysis of respiratory

musclesmuscles

20mA 20mA –– 40mA40mA “Shock current”, Muscle “Shock current”, Muscle

contractions, Breathing contractions, Breathing

affected affected

40mA 40mA –– 80mA80mA Rapid uncoordinated Rapid uncoordinated

contractions of heart muscles, contractions of heart muscles,

causing irregular heart beat, causing irregular heart beat,

possible death from asphyxiapossible death from asphyxia

>100mA>100mA Severe burns, muscular Severe burns, muscular

contractions, stoppage of contractions, stoppage of

heart, Death is certainheart, Death is certain

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SEVERITY OF ELECTRICAL SHOCK“Longer the victim is in contact with an electrical current the more serious is the

consequences”

Resistance Magnitude of

Current

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Path of Flow Duration

Voltage

Severity of Shock

SEVERITY OF ELECTRICAL SHOCK“Wet conditions are common during low-voltage electrocutions”

The presence of moisture from environmental conditions such as standingwater, wet clothing, high humidity, or perspiration increases the possibility oflow-voltage electrocution.

The level of current passing the human body is directly related to the resistanceof its path thro’ the body. LH finger tip to RH finger tip is a dangerous path.

Under dry conditions, the resistance offered by human body may be as high as100,000 Ohms. Wet skin may drop the body’s resistance to 1000 Ohms & below.

Moisture affects low-voltage electrocution

Voltage required for arc welding is low. Hence, welding cables, electrode holder& other parts of welding machine are to be handled carefully. These low voltagesare dangerous to life in hot weather when the welder is sweaty or when he is damp

Serious accidents occur particularly in wet surroundings like bath rooms. Aperson in good contact with live part & in touch with wet ground can not get separatedfrom live parts.

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Case Study – The man is electrocuted, while shifting an Al

ladder. Ladder touched 132 kV OH live conductors. “Ensure ladders are secure, stable and adequately supported to prevent them from contacting

a power line”

1. Prepare HI & RA for various

elect. Activities, new jobs

2. Prepare SOP of all hazardous

elect works in English/Hindi

3. Render training to electrical team

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3. Render training to electrical team

4. Procure suitable ladder of non-

conducting material

5. Barricade on both sides of OH

conductors

6. Display ‘CAUTION BOARD’

7. Barricade upstream and

downstream of OH lines to

prevent travel of any object

8. Organize strict supervision of

critical jobs

High Voltage Shock – Case Study

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Never go near a person or

equipment that is in contact with an

overhead power line

DANGERS FROM D C VOLTAGEAC voltage wave has higher peak value than DC voltage of same level, AC wave frequency affects frequency

of human heart beat, more dangerous. If the contact is of a very short duration due to throwing off the

person, life is saved.

Threshold values of DC are higher, let-go current - 6-7 mA

Painful shock but muscular control not lost - 50-75mA

Shock painful, severe muscular contraction, breathing affected –60-90mA (3s)

Shock – ventricular fibrillation, heart function irregularity too Shock – ventricular fibrillation, heart function irregularity too rapidly, heart muscles do not respond, pumping of blood is not accomplished, breathing stops, death is certain 500mA (10s)

Effect from DC is heat and electric burn produced by DC current may be serious & fatal when voltage is high

As a rule DC installations use supply voltages under 250V

Mr. G Frankel (while experimenting with dogs)

a) 120V d.c. hazards equal 42V a.c. hazards and

b) 108V d.c. hazards equal to 36V a.c. hazards

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AC shocks Vs DC shocks

1. AC current from external source flowing thro’ human body in mAcause sudden contraction of muscles.

2. Person in contact with the live line is unable to get detached (let-go)

3. Lung muscles get contracted, lung functions are adversely affected,breathing stopsbreathing stops

4. Shock currents above certain magnitude cause stoppage of heart, flowof blood to brain is stopped, victim dies within a few seconds.

5. Requires artificial breathing & heart-massage

6. Normal frequency of heart beat is 70 C/m. Frequency of normalrespiration is 12-16 C/m. AC supply frequency is 50C/s. Frequency ofAC supply is too large for lung/heart frequency Hence dangerous tolungs and heart

7. With DC shock currents the disturbance in frequency of heart is onlyonce

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ELECTRIC BURN“Passage of electric current thro’ conductor is with dissipation of heat.”

Electrical burn may be caused by passing of electric current thro’ body or by an electric arc

Heavy arcing may cause severe burns as the temperature of an electric arc is usually >350000 F

Dissipation of heat is directly proportional to I2Rt.

As the skin is the site of highest resistance in the body, it is there the burning is most likely to occur when contact with live conductor is mademost likely to occur when contact with live conductor is made

Such burns may be deeper than may first appear on clinical examination. Healing is slow and may be accompanied with much scarring.

Metallization or Crusting of the skin is the result of an electrolytic effect of current on human body, called “sign of current” or “crusts”.

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•Nerves at contact point may damage•Internal blood vessels clot,

•Muscle contraction cause skeleton fractures

ELECTRICAL BURN“The man came in contact with a live 6.6kV bus-bar”

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The picture is taken after 3 weeks of his

injury

BURNS CAUSED BY ELECTRICITY

1.The most common shock-related , non-fatal injury2. Burns are of three types : electrical , arc burn, thermal contact burns3. Caused when one touches a electrical wiring or equip used or maintained improperly4. Serious injury. Needs immediate attention. Clothes may catch fire, thermal burn may result

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Contact electrical burn. Electrical burn on hand and arm

Electrical Fires

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Risk from exposed live parts depends

on your distance from the parts .For

MV 1’ to 3⅟2’

CAUSES OF ELECTRICAL FIRES“Short circuit is not the cause but the effect of electrical fires”

Selection of improper or substandard equipment or material

Electrical installations are not in accordance with statutory regulations

Overloading of equipment

Maintenance negligence Maintenance negligence

Failure of insulation level

Damage due to rodents, termites and pests

Lightning strokes (single distinguishable current impulse of a flash exceeds 28000A, 5% times and 200 000A 1% time)

Water seepage

Static electricity

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Life hangs by “Thin Live Wire” frequently causing

electrocution and fires -Chandni chawk, Old Delhi

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Flying drums of fire in factory blaze in Industrial belt,

Dankuni, W B (11.07.2012)

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Welding spark started the fire in one of the oil drums that

exploded in air with deafening sound. More drums in the store

yard caught fire one by one and exploded after shooting up in air.

FIRE AND EXPLOSION“Never use aerosol spray cans around high-voltage equipment, use non-flammable CRC”

1. One technician was assigned the job

to clean the lower compartment of

elect cabinet using cleaning fluid in

aerosol can.

2. He began to clean the upper

compartment filled with live circuitry.

3. When cleaning spray contacted the

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live circuitry, a conductive path for

current was created.

4. Current passed thro’ the stream of

fluid, into technician’s arm, and

across his chest.

5. Current caused a loud explosion,

victim’s clothes were on fire

6. Victim died after 24 hours.

7. Before doing any electrical work, de-

energize the circuit & equipment,

perform LOTO, test circuits &

equipment to ensure that are de-

energized.

BLAZE GUTS PACKING UNIT(probably sparked by electrical short circuit)

• A packing unit of a reputable apparel onGrand Fore Road, Howrah was gutted in ablaze on 14. 07. 2012• The fire which broke out at 6.30 pm was

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• The fire which broke out at 6.30 pm wasprobably sparked by an electrical shortcircuit• Building was evacuated, no life was lost• Eire sprayed very fast to engulf the entirebuilding in 30min. It had inflammablematerials like plastic, paper cartons, andapparel• Barring a few fire extinguishers the placedid not have any fire safety measure• 20 fire engines struggled for 3hrs todouse the blaze

FIRE FROM ELECTRICITY IN A PAINT FACTORY

•Incidence happened on12th March 2014 inShalimar paint factory, Howrah•Fire broke out at 2.30 a.m. reportedly fromelectrical short circuit and took nine hours toquench after employing 30 fire tenders•Seven lakh liters of paints were burnt and

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•Seven lakh liters of paints were burnt andequipment were damaged in 112 year oldfactory. Raw materials, paper cartons andplastic containers were fully gutted•Eye witness informs he could see flames andsmoke from around 200m distance and hefelt that area was getting extremely hot outthere•Flames, fuelled by the inflammable paint,leapt up 40ft and were visible from 5km awayVidyasagar Bridge•No life loss or human injury is reported.•Root cause is under investigation

TRANSFORMER FIRE

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WHY TRANSFORMER EXPLODES?

The insulation in transformer fails and live current takes a short cut usually tothe ground

This is where things get incredible. In power transformer current begins arcingwhich contain huge amount of current – sometimes tens of thousandsamperes.

The temperature of an arc can reach 30 0000F far hotter than the surface of theSun, causes nasty problems. Circuit breaker do not trip

Electrical arc vaporizes transformer oil and creates a dynamic pressure whichtravels at a speed of 1200m/sec. The phenomenon occurs within few seconds. Apressure wave is generated, pressure becomes equal throughout the entiretransformer tank within 50 – 100 mili-seconds after the electrical arc. Causesthe tank to rupture.

Thick black smoke from fire is caused by vaporized copper combining withoxygen

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Cont:

Arc often melts internal parts, generally the series of coils, of the transformers.

Transformer mineral oil with a flash point of about 1490C in large quantities and high voltage in heavy duty transformers can be vaporized and turned into explosive gases like CO. These can be specially dangerous and explosive in a confined space

Mineral oil requirement in a moderately large transformer is roughly 2.3 liters per kVA

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Transformer capacity Mineral oil content

500kVA 818L

15000kVA 15,456L

FIRES IN POWER TRANSFORMER

1. Most fires are from internal fault in

Transformers

2. Do not locate transformers with oil

cap 2000 L in basement

3. If necessary to locate it in

basement it should be in a separate

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basement it should be in a separate

room of 4 hr fire rating with door of

2hr fire rating

4. Dedicated access to transformer

room from outside

5. Switchgears in separate room of 4

hr fire rating

6. Transformer with 9000 L oil to be

protected by automatic high

velocity water spray system & fire

barrier between transformers

FLASH BURN & FLASH OVER“Arcing faults produce large shockwaves that can blow personnel off their feet. Arc can produce very high temperature

Flashover is a sudden disruptive discharge of electrical energy through air (oroil or gas), caused by ionization of the path between two conductors atdifferent potentials. When the voltage withstand strength of the air-gapreduces below the applied voltage, gap breaks down and arc-flash occur.Mostly at over-voltages or switching surges. Arc produces large amount ofheat & large shock waves. Arc temperature may go up to 350000F

Exposure to high voltages result in burns at the sites where electrical current Exposure to high voltages result in burns at the sites where electrical currententers and exits human body.

Direct contact and arcing produce flame burns from the ignition of clothingor other combustible, non-electrical materials

Victim is subjected to:

1. Flame burn from arc

2. Electrical shock from passing current

3. Treatment can require years for skin grafting & rehabilitation. The victim maynever return to work/quality life/may die

“Stand a side of the panel to operate”

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Cont.

4. Arching gives off thermal radiation (heat up to 60000 F) and intense light,which can cause burns. Factors that affect the degree of injury, include skincolor, area of skin exposed, and type of clothing worn. Proper clothing, workdistances, and over-current protection can reduce the risk of burn.

5. A high-voltage arc can produce a considerable pressure wave blast. A person 2 feet away from a 25,000 amp arc feels a force of about 480lb on the front of the feet away from a 25,000 amp arc feels a force of about 480lb on the front of the body. May cause damage to ear and concussion.

6. A high-voltage arc can cause many of the Cu & Al components to melt. Hot molten components can be blasted to great distance, cause serious burns. Ordinary clothing can catch fire, even when 10ft or more away.

“Where work is performed in locations containing uninsulated energized overhead lines that are not guarded or isolated, precautions shall be taken to

prevent employees from contacting such lines directly with any unguarded parts of their body or indirectly through conductive materials, tools, or

equipment. Where the work to be performed is such that contact with un-insulated energized overhead lines is possible, the lines shall be de-energized

and visibly grounded at the point of work”

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FLASH BURN

To start of work on hot lines employ trained worker, de-energise, perform

LOTO, use proper PPE, Don’t use aerosol spray in hi-volt equipment

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Arm with third degree burn from H V

supply lineFire due to contact with HV

power line

CIRCUIT PROTECTIONS

This is an automatic switching device used for the protection of a circuit against O/L and S/C 1. Has dual trip, thermal & magnetic,

thermal operates for O/L ; magnetic

operates on S/C

2. MCB can not be made ‘ON’ during HRC Fuse

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2. MCB can not be made ‘ON’ during

fault condition

3. Has high making & breaking capacity

4. It is used in place of fuses in DBs for

protection of individual circuit

5. Available in Voltage Rating – 415/240 V

and Current rating 0.5, 1, 2, 4, 6, 10, 16,

20, 25, 32, 40, 50 & 63 A.

MCCB & MCB

SAFETY HAZARDS IN CABLE GALLERIES

Cable galleries are one of the most sensitive areas , susceptible to major firehazards resulting in colossal loss to industry. Such catastrophic situation ariseon account of apathy or scanty towards planning, design, construction, upkeep& maintenance of cables in gallery

Haphazard laying of cables and cable trays, lack of fire safety doors and markedescape ways, absence of sufficient number of fire quenching equipment,escape ways, absence of sufficient number of fire quenching equipment,improper ventilation to maintain it dry, cool & dust free, water logging, accessto rodents and reptiles, storage of unwanted & fire prone materials, proximityto hot production units are key parameters leading to major hazards in cables.

Electrical cables are generally insulated with polyvinylchloride whichcontribute to rapid fire spread, giving off highly toxic products like smoke,hydrogen chloride, hydrochloric acid that cause damage to equipment,structures and reinforcement

Quenching cable fires with water aggravates corrosion when RH exceeds 65%

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CABLE SAFETY & CONTROLS

Place HV power cables at top, LV power cables at middle and control and instrumentation cables at bottom arms of cable structure, use separator

Cable gallery floor should be provided with slope leading to sump with sump pump for dewateringsump pump for dewatering

Provide emergency lighting inside cable cellars

Avoid welding, cutting and using naked fire inside cable gallery

Segregate cable runs to compartments. Avoid cable joints in overhead cable racks and in trenches

Avoid cable runs in close proximity to steam lines and hydrocarbons at high temperature

Carry out maintenance, upkeep, condition monitoring & routine IR testing of cables with due diligence

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STATIC ELECTRICITY. What is it?

The phenomenon, technically known as electrostatic electricity, is usually anuisance hazard – but it can cause fires and explosions when built up chargeeventually develops enough energy to jump as a spark to a grounded or lesshighly charged object in an attempt to balance the charge

Electro static energy is ordinary electricity existing and flowing in circuits thatgenerally are non-electricalgenerally are non-electrical

A static electricity hazard exists under following conditions in combination

I. Electrostatic charge must be generated

II. The charge must have accumulated in a liquid or solid causing an electric field in a gas mixture

III. The static field must cause a spark with an intensity sufficient to ignite the gas mixture

IV. Gas mixture must be flammable

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HAZARDS OF STATIC ELECTRICITY“The primary source of electrostatic charge is contact electrification where two dissimilar materials are

brought into contact and then separated, carrying equal and opposite charges”

GENERATED BY CONTACT/SEPARATION OF DISSIMILAR MATERIALS CARRYINGEQUAL & OPPOSITE CHARGES – flow of liquids thro’ pipes, flow of liquids thro’strainers or filters (mesh size-350), stirring and mixing motion

CREATE FIRE/EXPLOSION BY SPARK DISCHARGE – a discharge between liquid orsolid conductors, when field strength between them exceeds a level known as‘breakdown strength’

FLAMMABLE LIQ. IN AIR VULNERABLE TO SPARK - In any situation where FLAMMABLE LIQ. IN AIR VULNERABLE TO SPARK - In any situation where explosive risks are present (solvent, vapors, gases, dusts) the possibility of static electricity buildup and discharge by spark is a hazard.

CAUSE ELEC. SHOCK SAFETY BY EARTH CONNECTION, PASS CHARGE TO EARTH BONDING/EARTHING RECOMMENDED, low resistance

“If the charge is large and the air humidity low, an instant sparking discharge between the equipment parts or into earth may ignite a flammable material or a combustible mixture. A spark marking an electric discharge of 3000V can ignite all vapor & gas-air mixture in a room

”

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CONTROL OF HAZARDS FROM STATIC CHARGE

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1. Prevent charge generation2. Impossible? Don’t allow retention of charge on a conductor, stored energy

can be released in a single spark to earth or to another conductor3. Connect all conductors to each other and to earth by electrical paths with

sufficiently low resistances to permit relaxation of charges4. Recommended grounding resistance for the control of static electricity in

electrical area of classification zones 0, 1, 2 is 10ohm (max)5. Control environment

BONDING AND GROUNDING WHILE TOP

LOADING A TRUCK TANK

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A CASE STUDYHYDROCHLORIC ACID TANKER EXPLODED

Finding on investigation:

1. On an occasion HCl was being transferred to a road tanker , when there was an explosion. The dished-end of the tank fractured from its welded rim-joints , was dislodged and flew into the air to a distance 60m.

2. HCL reacts with iron, in peculiar conditions, gives out nascent hydrogen2. HCL reacts with iron, in peculiar conditions, gives out nascent hydrogen(H+), forms flammable mixture with air, which on receiving ignition sourceexplodes.

3. In this instance case rubber lining , inside the tank at some places, hadgiven way and M S body was exposed to acid. Reaction with Fe++ evolvedhydrogen.

4. Static was formed by the flow of non-conducting liquid and a sparkdischarged between the body of the liquid and grounded metal tanker.

5. Static spark provided the ignition source

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EQUIPMENT EARTHING & NEUTRAL EARTHINGEarthing is an integral part of any electrical installation. Earthing system still remains a complex

and confusing subject. It is so common, yet so little understood.

All elect apparatus using a.c. or d.c. supply regardless the voltage and installed atworkplace where risk of exposure is expected should be grounded to generalmass of earth at two distinct & separate earth points

When the body, frame, structure or any metallic part is connected solidly to earthelectrode, the voltage of that part does not rise to dangerously high value duringleakage currents or earth faults.leakage currents or earth faults.

Earth fault operates fuse or circuit breaker. Severe shock is prevented.

Neutral earthing is connecting to ground the neutral point of star connectedwinding

“As a rule provide neutral earthing at every voltage level “

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NEUTRAL GROUNDING

Types of Grounding

1. Ungrounded system – Used in continuous process industry

2. Solid Grounded – The neutral is directly connected to ground without anyintentional impedance between the neutral & ground

3. Resonant Grounding - An adjustable reactor of correctly selected value to3. Resonant Grounding - An adjustable reactor of correctly selected value to

compensate the capacitive earth current is connected between neutral &earth

Method of Grounding

1. Direct solid grounding

2. Earthing voltage transformer primary. Earth fault relay is connected acrosssecondary of VT. Reactance of VT limits the earth fault current

3. Earthing via current transformer in series with grounding resistor.. The earthfault relay is connected to secondary of CT. Grounding resistor limits thefault current.

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EARTHING SYSTEM“Connect neutral points of transformers & generators to ground”

1. All non-current carrying parts

connected to earth system,

uniformly at ‘0’ potential

2. Floor on which O & M staff move

shall be at Gr. Potential, safe step

potential

3. During any earth fault in the Sub-

station the potential of structures,

47

station the potential of structures,

tanks, & other non-current

carrying parts does not rise to

unsafe value, i.e. safe touch

potential

4. Substations to comprise

• An earth mat or grid to cover

entire S/S area

• E/electrodes driven vertically into

earth at several locations,

connected to earth mat

• Riser connection between

structures, equip bodies, and

earth matIS 3043 : 1987

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EQUIPMENT EARTHING IN SWITCHYARDrelates to the low resistance connection by which the frames, enclosures, structures and other

non-current metallic parts are interconnected and earthed

1. Ensure freedom from

exposure to danger of

electrical shocks to

persons working in

electrical plant

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electrical plant

2. Provide current carrying

capability, for flow of

earth fault current of

specified magnitude and

duration, thus allowing

over current protection,

without fire, damage,

explosion

Maximum allowable ER

Major power station-0.5Ω, Major sub-station-1.0Ω, Minor sub-station-2Ω, MV network-2Ω,

LA-4Ω, Distribution Transformer-5Ω, HT pole-10Ω

PORTABLE ELECTRIAL TOOLSElectrical drills, grinders, saw, polishers etc.

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•Provide an earthing connection from the body of the tool & connect to proper earth

•The tool, flex lead wire & the earth wire should be inspected for condition check before use

•3-pin plug-socket should be used

•Double insulation (functional + protective) hand tools are now available for use

•Fault protection relays viz. RCCB (IS : 12640 – 2000)may be connected to interrupt supply if

fault exists

•Use of RCCB in every low voltage installations conforms to IE Rules 61(A),1956

•Factory set at 30mA

SAFE USE OF ELECTRICAL TOOL

CHECK-LIST

•LOW VOLT EQUIP IN TANK,WET AREA •INSPECTED, WELL MAINTAINED•MOTOR IN HEALTHY CONDITION

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CONDITION •APPROVED TOOL USED IN EXPLO COND •TOOL KEPT WELL , DID NOT FALL INSULATION, PLUG UNBROKEN •CORD PROTECTED FROM TRUCK, OIL •GROUND WIRE FASTENER IS SAFE •3-WIRE, PLUG EXTN CORD IN USE •GROUND WIRE USED,CHECK CONN GUARDING/FACE PROTECTOR IN USE

Man dies of electric shock

TEMPORARY FLOOD LIGHTS & HANDLAMPS“It is safe to use two lamp line tester, single lamp tester shall have transparent cover”

Normally provided & maintained for safe working during construction,maintenance, repair or demolition activities at passage ways, stairways &areas where workers are required to work, assemble or pass

It does not mean a reduced level of safety or quality; but should conformto certain criteria of electrical work, IE Rules. (IER 61)

Such work must have approval of a authorized person and a tag Such work must have approval of a authorized person and a tagmentioning the date & period of such wiring should be attached with itat prominent location

Normally two wire 1-ph line is used without an earth wire installation,creating a dangerous situation. Temp flood lights & hand lamps shouldhave earth connection or RCCB/RCD

Only 24V hand lamp should be used whenever

there is work inside a closed vessel, tunnel, gas

pipeline, excavation work, etc. (IER -36, IFA -36A)

Check the condition of lead wire for good health

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ELECTRICAL SAFETY DURING ARC WELDING“Arc welding & cutting operations exceeding 30A present problems of U/V radiations”

1.The welding lead shall be free from joints/splices up to 3m from electrode holder2. Use weld lead as short as possible, attach firmly to holder3. Holder which welder grips to have adequate insulation (volt to ground)insulation (volt to ground)4. Welding current to return to m/c by return cable.No wire rope/rod5. Pipeline transporting flammable liquid/gas not used as return path6. Voltage requirement of arc-welding is low, nevertheless sufficient to cause shock injurious to life. Most dangerous in hot summer/sweating7. Use PPE like welders gloves, shoes, welding shield, apron etc.

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ELECTRICAL ARC WELDING ARRANGEMENT

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FLAMEPROOF ELECTRICAL EQUIPMENTS

“A factory, where inflammable gas, vapor & dust is possible, intrinsically safe, explosion proof fittings and

junction boxes are used. Intrinsically safe elect equip are designed in which any spark or thermal effect in fault

condition is not capable of causing ignition of given explosive condition”

ZONE ‘0’ – area where flammable atmosphere is present continuously, e.g. inside ofcontainers, reactors. Use no or intrinsically safe equip, incapable to cause ignition innormal operation.(IS:5780-1980) [type of protection – Ex ia]

ZONE ‘1’ – area where flammable atmosphere is possible in normal operation, use equip.as in zone-0, flameproof equip. (IS:2148-1981), pressurized by inert gas (IS:7389-1976),Oil immersed (IS:7693-1975) [Type of protection – Ex ib, d,e,p]Oil immersed (IS:7693-1975) [Type of protection – Ex ib, d,e,p]

ZONE ‘2’ - area where flammable atmosphere is not likely to occur in normal operationOccurs for short time only, use equip. as in zone-0, use non-sparkingtools/apparatus.(IS:8289-1976), Increased Safety (IS:6381-1972) [Type of protection – Exn, o q]

“Intrinsic Safety – A circuit or part of a circuit is intrinsically safe when any spark or thermal effect produced normally i.e. by breaking or making the circuit or accidentally by short circuit or earth fault is incapable of

causing ignition”

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ELECTRICAL FITTINGS IN HAZARDOUS AREA

•All elect wiring in a hazardous area shall be effectively

sealed at all joints, mechanically protected against

damage

• Approved armored cable, complete with armour

clamps to provide mech support & elect continuity shall

be used

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be used

• Earthing & Bonding – 4 ohm in case of elec.

sys/equip/valve that operates protective device and 10

ohm for non-current carrying metallic parts of

apparatus

Ex i : Intrinsic safety

Ex d: flameproof

Ex e : Increased

safety

Ex p : pressurized

Ex o : Oil immersed

Ex q : Powder filling

Ex n : No sparking

All flammable liquids vary in volatility and have a flash point

below 930C and vapor pressure not exceeding 2.81kg/m2.

Class A: flash point <230C. Produce large volume of vapors

when released in open

Class B: flash point between 230 and 650C. Liquids are heavier

and less volatile and have FP slightly below normal ambient

temp.

Class C: FP between 65 and 930C. These liquids are low in

hazards as the rate of release at normal ambient temp in nil.

SAFETY PRECAUTIONS AND RISK CONTROL

Use wires of proper size & proper insulation in accordance with IS

Don’t use loose & temporary wiring for power supply to lighting, machine,apparatus. All temporary elec. installations to be routed thro’ RCCB/RCD (IS:12640)

All electrical equipment, switches, welding machine, elect tools should beproperly & distinctly grounded preferably at two points. IER-67(i)properly & distinctly grounded preferably at two points. IER-67(i)

Voltage & current ratings should be prominently displayed at installations

HRC fuses and not rewirable fuses should be used for all power connections

No live wire should be laid on the ground or wet surface. They should be atleast 3.5m above floor level

All electrical joints should be sound & properly insulated

Protect elec. installations from water & direct flame

Only competent/authorized person (IER-3,4)should attend elec. defects,B/D, S/D

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SAFETY PRECAUTIONS AND RISK CONTROL

Insulated/tested right tools should be used to attend repair of elec. lines

Recommended rubber mat should be kept in all switch rooms for C/Boperation (IS: 5424-1969, IS:15652-2006)

In case of elec. fires source of supply should be cut-off immediately

Proper shut down system & PTW should be followed while undertakingrepair or cleaning work in elect equipments. Recommended ‘TAG’ to beused.repair or cleaning work in elect equipments. Recommended ‘TAG’ to beused. (May follow NFPA 70 NEC Code, lock-out & tag-out procedure, part II, appendix E)

Metallic ladder should not be used unless insulated, instead use wooden one

Work on MV or HV conductors, equipment should be done after makingthem DEAD, short circuited and earthed

While erecting scaffold always keep 5.0m distance from OH transmissionlines

In stacking and handling of pipes and other conducting materialsprescribed safe distance should be maintained from OH lines i.e. up to 11kV– 1.4m; (+)11kV – (-)33kv – 3.6m; (+)33kV – (-) 132kV – 4.7m etc.

Test earth resistance value of mat/electrode in a dry day of dry season

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LOCKOUT and TAGOUT PROCEDUREmultiple energy sources, multiple crews, multiple locations, different disconnecting means, particular

sequence, continues for more than one work period

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•Turn off the power supply

•De-energize and lock-out the switchgear

•Tag out (IS 8095-1976) the circuit with an easy-to-see sign or label to

everyone know that someone is working on the circuit

LOCK-OUT AND TAG-OUT CHECKLIST

Identify all sources of electrical energy for the equipment and circuits in question

Disable backup energy sources such as Generators and Batteries

Identify all shut-offs for each energy sources

Notify all personnel that equipment and circuitry must be shut off, locked out and tagged out (simply turning a switch off is not enough)

Shut off energy sources and lock switchgear in ‘off ’ position. Each worker should apply Shut off energy sources and lock switchgear in ‘off ’ position. Each worker should apply his individual lock. Do not give your key to anyone

Test equipment and circuitry to ensure to make sure that de-energized. (this must be done by a qualified person)

Deplete stored energy (for example, on capacitors) by bleeding, blocking, grounding etc.

Apply tag to alert others that the energy source of equipment is locked out

Make sure everyone is safe and accounted for before equipment & circuitry are unlocked and turned back on (only qualified person will determine when it is safe to re-energize)

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SAFETY REQMT AS PER I.E.RULE

SERVICE LINE, APPARATUS OF SUFFICIENT RATING

MATERIAL AS PER I.S

SUPPLIER TO EXAM FITNESS OF SERVICE LINE, FITTINGS

SERVICE LINE OF GOOD INSULATION, STRENGTH

SUPPLIER TO PROVIDE CUTOUT, EARTH, N/EARTH

BARE CONDUCTOR TO BE INACCESSIBLE

AFFIX DANGER NOTICE

HANDLING? MAKE IT OFF, EARTH, DISCHARGE, Ensure Twice

USE GLOVES (36kV for linemen),E/SHOES ,TESTER,HELMET (tested at 20kV), E/DEVISE

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OVERHEAD LINE CLEARANCE

ACROSS STREET– LV/MV- 5.8m. HV-6.1m

ALONG STREET -- LV/MV-5.5m, HV-5.8m

ELSEWHERE– L/M/H (bare-4.6, insul-4.0, >11kV-5.2m)

CROSS TRAMWAY (L/M-1.2m),upto11kV - 1.8m, >11kV-2.5m

BUILDING, PASSES (L/M), -2.5m, ADJACENT-1.2m, HV up to 33Kv– 3.7m and 2.0m

SPAN(mt) SAG(mt)

LV/MV 50-80 0.6-1.0

11KV 100-130 1.0- 1.5

132KV 260-360 5.0- 7.0

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OVERHEAD LINE CLEARANCE

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CLEARANCE OF O/H CONDUCTORS

VOLTAGE Ph/E Ph/Ph

6.6kv 140mm 178mm

11kv 178mm 229mm

33kv 381mm 431mm

132kv 1270mm 1473mm

400kv 3065mm 5750mm

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SAFETY CLEARANCE FROM LIVE CONDUCTOR

System Voltage kV, rms, Ph to ph Min Safety Distance from HV lines

Up to 33 kV 0.8m

66kV 1.0m

132kV 1.4m

220kV 2.1m

275 kV 2.4m

400 kV 3.1m

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Handling and Stacking of Materials under

O H Lines

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The absolute limit of approach for all O H power lines is 6m i.e. all parts of the

crane should be at least 6m away from the O H lines

If any work is taken up after dark, notices and cross bar should be illuminated

Plant passing under O H lines

Value of ‘H’ for different voltages

1. Low & Medium Voltage – 1.2m

2. High Voltage line up to 11kV – 1.8m2. High Voltage line up to 11kV – 1.8m

3. High voltage lines> 11kV - 2.4m

4. Extra high voltage lines - 3.0m

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ELECTRICAL HAZARD CONTROL PRINCIPLES

Inspect/evaluate the electrical equipment

Maintain the electrical equipment’s insulation and enclosure integrity

Plan every job and document first-time procedures

De-energize, if possible

Anticipate unexpected events

Identify and minimize the hazard

Protect the employee from shocks, burn, and blast, and other hazards that are due to the working environment

Use the right tools for the right job

Assess people’s abilities

Audit these principles

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ELECTRICAL HAZARD CONTROL PROGRAM

Every electrical conductor and circuit part is considered energized until proven otherwise

No bare-hand contact is to be made with exposed energized electrical conductors or circuit parts above 50V to ground , unless the ‘bare-hand method’ is properly used

De-energizing an electrical conductor or electrical part and making it safe to De-energizing an electrical conductor or electrical part and making it safe to work on is in itself a potentially hazardous task

Employer develops programs, including training and employees apply them

Use procedures as “tools” to identify the hazards and develop plans to eliminate/control the hazards

Train workers to quality them for working in an environment influenced by presence of electrical energy

Identify/categorize tasks to be performed on or near exposed electrical conductors, Identify & use precautions appropriate to the working environment

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RECOGNIZE ELECTRICAL HAZARDS“must know which situation can place you in danger”

Conduct JHA, Assess Risk, Prepare SWP

1. Inadequate wiring is dangerous

2. Exposed electrical parts are dangerous

3. Overhead power lines are dangerous

4. Wires with bad insulation can give you a shock

5. Electrical system and tools that are not grounded or double insulated are dangerousdangerous

6. Overloaded circuits are dangerous

7. Damaged tools and equipment are electrical hazards, can cause overloads, expose you to live electrical parts

8. Using wrong PPE is dangerous

9. Some on-site chemicals are harmful

10. Defective or improperly set up ladders and scaffolding are dangerous

11. Ladders that conduct electricity are dangerous

12. Electrical hazards are made worse if the worker, location, or equipment is wet

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