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Electrical Safety

Introduction

Rural and domestic electrical systems cause many injuries and electrocutions each year.

– Electrocutions are 5% of worker deaths.

– 40% of deaths caused by contact with overhead power lines.

It is important to know how to work with and around electricity safely.

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Electrical Safety

1 Safety is freedom from accidents.2 Accidents are caused by hazards.3 Whenever humans are exposed

to hazards there is a potential (risk) that the hazard will cause an accident.

4 Humans are always exposed to hazards.

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Conclusion: Humans are always at risk.

How do we prevent electrical accidents.

Electrical HazardsFour (4) primary electrical

hazards

– Burns

– Shock

– Ventricular fibrillation

– Electrocution

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Electrical Burns

1 Electricity passing through resistance generates heat.2 Human tissue has resistance.3 Electricity passing through human tissue can generate

sufficient heat to destroy the tissue.

€

Electrical energy= duration xvoltage2

resistance

What principles of safety does this equation demonstrate?

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Electrical shock

1. An electrical shock is defined as sufficient current to be detected, but insufficient current to cause tissue or nerve damage.

2. Injuries are usually secondary because the electrical shock causes the muscles to contract.A. Knock off ladderB. Strike against objects

Current(mA)

Effect

1 Threshold of sensation

5 Disturbing shock, muscular control maintained

6 – 25 Muscular control lost in women, maximum let-go range for women

9 - 30 Muscular control lost in men, maximum let-go range for men

30 Respiratory paralysis

75 Fibrillation threshold, 0.5%

250 Fibrillation threshold, 99.5%

4,000 Heart paralysis

>5,000 Tissue burning

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Ventricular fibrillation

120V, 60 hertz currents as low as 60 mA passing through the chest can stop the heart from working effectively.Currents over 200mA cause the heart muscles to seize.

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Electrocution

The lethality of an electrical shock is influenced by six factors.

1 Magnitude of Current2 Duration3 Frequency of current4 Pathway5 Phase of heart cycle6 Body mass

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Managing Electrical Risk

Electrical risk is manage by following best management practices for electricity.

What are the best management practices for electricity?

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Codes and Safety

1 The source of information for the safest installation of electrical service and components is the National Electric Code (NEC).

– Published by the National Fire Protection Association (NFPA).

2 Note: many rural areas do not have local or state agencies to enforce NEC regulations. But:

– The NEC should be used for safety reasons and because insurance companies may deny coverage or charge a higher rate for buildings that do not met NEC standards.

3 Example: Minimum clearance distance for grain storage bins or buildings (Table 1-1.)

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Resources

http://www.osha.gov/SLTC/electrical/index.html

http://ehs.okstate.edu/modules/electric/index.htm