Hazards of Electrical Energy

1.0    Hazards of Electrical Energycan be broadly classified into three broad groups:

           (a) Shock

           (b) Burns and

           (c) Fire or explosion

1.1 Electric Shock:

Electric shock is a term that relates to the consequences of current flowing through nerves, muscles and organs of a body. When victim is in contact with live part for long time, body tissues can get damaged by burns. Danger with Alternating Current (AC) is that, it often causes the person concerned to maintain an involuntary grip on the live object and this

prolongs the current flow.

If the rhythm of the heart is disturbed, it can cause death. This is known as Ventricular Fibrillation. It results in reduction of oxygen supply to the brain. If brain does not get fresh blood for more than three minutes, it can result in death. Unless skilled attention is given immediately by artificial respiration, ventricular fibrillation can be irreversible.

Heart is very important part of our body. In the average life span of 70 years, heart beats about 2500 million times and pumps 227 million liter of blood. During electrical shock, current passing through heart and time for which current passes, play deciding role.

Personal sensitivity to electric shock varies from person to person. It also depends on age, sex, heart condition etc. Even for the same person, electrical shock depends on many factors.The severity of electrical shock is the function of the current (mA) and the time for which it flows through the body. 50 mA current can flow for 200 mS through the body without much danger, whereas 500 mA current even for 50 mS could be fatal.

1.2 Burns

Burns can be due to one of the two reasons – due to current passing through the body or due to tremendous heat energy generated by Arc Flash. In the second case, the victim might not become current path, but he gets severe burns due to heat generated by flashover.

(a) Burns are divided in to three categories:

• 1st Degree Burns: Only outer layer of skin is burned. Injury is not all the way thro’ 1^stlayer
• 2nd Degree Burns: Outer layer burned through and second layer also has burned
• 3rd Degree Burns: All layers of the skin are burned. Fat, muscle, bone etc. also can be affected

(b)  What Causes Arc Flash?

• Dust, impurities, animals, corrosion at contact surfaces producing heat, loosening contact and creating sparks.
• Sparks produced during racking of breakers, replacement of fuses, accidental touching or Dropping tools
• Accidental touching and dropping of tools, nuts-bolts, or metal parts.
• Over-voltages across narrow gaps
• Failure of insulating materials
• Tracking across insulation surfaces
• Equipment failure
• Inadequate short circuit ratings
• Breakers/fuses closing into faulted lines.
• Snapping of leads at connections due to force – human, rodents or birds.
• Improper work procedures

(c) Tasks with Potential for Arc Flash are as under:

• Operating a switch or circuit breaker
  • Inserting or removing a circuit breaker
  • Opening an enclosure door
  • Removing a cover (bolted or hinged)
  • Testing for voltage

(d) Arc Flash Injuries

   If an arc flash occurs near you, you can be:

• Electrocuted
  • Burned
  • Blinded
  • Injured by the blast and suffer:
• Shrapnel wounds
• Lung blast injuries
• Ruptured eardrum
• Pressure wave injuries.

Workers may never regain their quality of life and may even die from exposure to an arc flash event.

(e) Severity Factors

There are three main factors deciding the damage & injury by Arc flash.

• Power – amount of energy at the arc
• Distance – of the worker to the arc
• Time – duration of the arc exposure

Temperature of Arc flash is more than even sun temperature. Temperature of the surface of the sun is @ 5482 Deg. C. Temperature of the arc is 19444 Deg.C!      

(f) Probability of Surviving Burns

Two main factors playing part in survival are:

• How much area of body has been affected by arc burns and
  • Age of the victim.

Fig.1 (below) shows the % survival based on these two factors. It can be seen that as the age increases, survival chances gets comparatively reduced.

Fig.1 % survival after Arc Flash accident

(g) Steps for prevention are as under:

• Carry out Arc Flash Hazard Analysis
• Control Arc Flash Hazards at the source, along the path & at the worker.
• Include Electrical Safety in your Occupational Health and Safety Management Program.
• Use an electrical work permit system.
• Conduct regular equipment maintenance and label equipment that poses a flash hazard.
• Confirm single-line diagrams for accuracy and available fault current.
• Maintain documentation process.
• Provide training and job briefings.
• Conduct periodic safety audits.
• Apply hazard labels describing required PPE and boundaries for equipment use.

1.3 Fire or explosion

In case of heat generated by power electricity (overload, short circuit or earth fault) or static electricity (spark) or lightning, fire can take place. In case of flammable materials, it can cause explosion also.