OFS QHSE Electrical 1

Revalidated on: 29 March 2005

QHSE-Electrical-1-1 Owner: WCP

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Electrical Safety Level 1

• The objective of this presentation is for the student to understand the risk associated with electricity, and how they can be minimized.

• The audience is selected employees exposed to the electricity risk, and the requirement is assigned locally.

• Carefully read this presentation, you then MUST take the online test; on passing this test your QUEST certification will be updated accordingly

• If you have questions, contact your local QHSE support



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Schlumberger shall continually evaluate the risks to our workforce, our clients and the environment. Comprehensive risk assessment will provide the necessary information to reduce risk and mitigate the impact of our operations on Health, Safety and the Environment.

Commitment, Leadership and Commitment, Leadership and AccountabilityAccountability

Policies and ObjectivesPolicies and Objectives

Organization and ResourcesOrganization and Resources

Contractor and Supplier Contractor and Supplier ManagementManagement

Risk ManagementRisk Management

Business ProcessesBusiness Processes

Performance Monitoring & Performance Monitoring & ImprovementImprovement

Audits and ReviewsAudits and Reviews

ImprovemImprovementent

ControlControl

CorrectioCorrectionsns

Understanding Electrical Safety



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What is Electricity ?

• Movement of positively or negatively charged particles

• Analogy with water flow– Water reservoir Battery, Generator, Power

station– Pipe Electrical conductor



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What is Current ?

• Flow of electric charge, or electrons– Flow : quantity of water through pipe in a

given amount of time.– Current: quantity of electrons through

conductor in a given amount of time.

• Measured in amperes• Two types

– DC or direct current (flows in one direction only).

– AC or alternative current (flows in two directions at specific rate).



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What is Resistance ?

• Resistance is like friction for water– Larger wires have less resistance than smaller

wires.

• Resistance induces a drop in voltage• Resistor is a conductor with a given

resistance



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Ohm’s Law

• Current flows in an electric circuit in accordance with several definite laws

• Ohm’s law states that V = I * R, where :– V is the voltage in volts– I is the current in amperes – R is the resistance in ohms

• Ohm’s law applies to DC and AC currents



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Hazards of Electricity

• Five primary hazards :– Shock– Burns– Arc-Blast– Explosions– Fires

• Danger signs for electrical hazards



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Shock

• Human body becomes part of current flow• Direct effect

– Injury or death can occur whenever electric current flows through the human body. Current less than 30 mA can result in death.

• Indirect effect– Human reaction to current flow may result in falls, or

movements into operating machinery.

• Three basic ways:– Contact with both wires of an electrical circuit.– Contact with one wire of an electrical circuit and the ground

source– Contact with ground source and a metal part that is in contact

with a wire of an electrical circuit.



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Burns and Arc-Blast

• Burns– Occurs when a person touches electrical wiring or

equipment that is improperly used or maintained (typically on the hands).

• Arc-Blast– Occurs from high amperage currents arcing

through air.– Temperature as high as 35,000 F have been

observed.– Hazards associated with arc-blast:

• Thermal Radiation• Pressure wave• Projectiles



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Explosions and Fires

• Explosions– Occurs when electricity provides a source of ignition

for an explosive mixture in the atmosphere.– Ignition can be due to overheated conductors or

equipment.

• Fires– Electricity is one of the most common causes of fire

both in the home and workplace.– Defective or misused electrical equipment is a

major cause, with high resistance being one of the primary source of explosion.

– High resistance connections occur when wires are improperly spliced or connected to other components (outlets and switches).



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Effects of Shocks

• The effects of electric shocks on the human body depends on :– Current and voltage– Resistance– Path through body– Duration of shock



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Current and Voltage

• Detrimental effects are due to current flowing through the body. With increasing alternating current :– Tingling sensation– Contraction of muscles and sensation of heat– At 15 mA victim cannot let go of the conductive

surface• let-go threshold

– At 100 mA ventricular fibrillation of the heart occurs … until death

• Heavy current flow can result in severe burns and heart paralysis.



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Resistance and Path through Body• Resistance

– Electrical resistance of human body varies with :• Amount of moisture on skin• Pressure applied to contact point• Contact area

– Wet condition will drastically reduce resistance– Shock severity increases with increasing

pressure– The larger the contact area, the lower the

resistance

• Path through body– Affects the degree of injury– More severe if heart is in the path (flow from

hand to feet)



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Duration of Shock

• Duration of shock has a great bearing on final outcome– Short : may only be a painful experience– At fibrillation threshold, a duration of a few

seconds may be fatal– At high currents, death is inevitable if shock

has appreciable duration



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Summary of Effects

• Current flow greater than the "let go" threshold of an individual may cause a person to collapse, become unconscious and can result in death.

• Current flow through the chest, neck, head, or major centers controlling respiration may result in a failure of the respiratory system.

• The most dangerous condition can occur when fairly small amounts of current flow through the heart area.

• Extensive tissue damage, including internal organ damage due to high temperatures, occurs when very large

currents flow through major portions of the body.• There are recorded cases of delayed death after a person

has been revived following an electrical shock. This may occur within minutes, hours, or even days after the event has occurred.



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Minimizing Electrical Hazards

• Electrical hazards can be minimized. There are various ways of protecting from electrical hazards.– Locking and tagging equipment

• Source of electrical energy isolated from equipment undergoing repair or maintenance

– Guarding• Live parts of electrical equipment operating > 50 volts

must be guarded against accidental contact• Entrance to rooms containing exposed live parts must be

marked with warning signs forbidding unqualified persons to enter

– Grounding • A low resistance path to earth is created• Avoid build up of voltage which may result in dangerous

shocks• Reduces probabilities of accidents



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Minimizing Electrical Hazards ...

– Mechanical protection device• Designed to shut off the current in the event of a ground fault,

overload, or short circuit in a wiring system• Ex: ground fault circuit interrupters, fuses and circuit breakers

– Personal Protective Equipment• Specific PPE for electrical workers

– Safety work practices• Good judgment and common sense• Operate equipment in accordance with manufacturer’s

recommendations• Unauthorized personnel shall not occupy areas around switch

gear, panel boards, or load centers• When working with electrical equipment, always work with a

partner• Where live parts present an electrical hazard, employees may

not perform housekeeping duties close to the parts, unless protected



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– Electric cords• Inspect cords regularly for signs of stretching, insulation damage

and kinking.• Never carry an electrical tool by its cord.• When using tools requiring a third wire ground, only use three

wire extension cord with three-pronged, grounding plugs and three holes electric outlets.

• Always remove the cord at the plug. Do not pull on the cord.• Always use the correct extension cord for the job. An undersized

cord can cause a drop in tool power and overheating.• Hands must be dry when plugging and unplugging flexible cords.

– Plugs and Receptacles• Electric plugs and receptacles are designed for different currents

and voltages, so that only matching plugs and receptacles will fit together.

• Beware of standards changing from country to country.



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– Connecting a portable computer• Connect the AC adapter to the PC power jack.• Connect one end of the power cord to the AC

adapter.• Connect the other end to the power outlet.

– Hazard with portable computer• Do not use your computer in or near water (to

avoid the danger of electrical shock).

OFS QHSE Electrical 1

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Transcript of OFS QHSE Electrical 1