Student safety 2011 5th edition - Pt 2 - Pg 5-6

Question 1

How can electricity jump from one conductor to another and what is it called?

Pg 7

Answer 1

Electricity can jump from one conductor, through the air to another conductor–called an arc?

Question 2

True or false?
Lightening is an extreme example of a natural arc?

Pg 7

Answer 2

true

But Wikipedia claims natural lightning as electric sparks, not an arcs.

Question 3

What’s electric welding?

Pg 7

Answer 3

A phenomenon, where a small arc of electricity occurs every time a switch is opened or closed, is called arcing/switching arc.

Question 4

Electricity wielding what to join metal pieces together by melting?

Pg 7

Answer 4

Electric welding uses a controlled arc to join pieces of metal together by melting them.

Question 5

What occurs each time you open/close a switch?

Pg 7

Answer 5

A small arc occurs each time you open or close a switch.

Question 6

What occurs in equipment feailures and what is it called?

Pg 7

Answer 6

Some types of equipment failures result in a large, uncontrolled arc known as an “arc flash.”

Question 7

Where can serious arc flash incidents occur and why?

Pg 7

Answer 7

Serious arc flash incidents often occur in buildings/ industries/utilities with high power.

Question 8

What happens in an arc flash?

Pg 7

Answer 8

an explosion with large amounts of heat can have fatal causes for unprotected ones
But such incidents are rare.

Question 9

An electric park can make how much temperature?

Pg 7

Answer 9

Temperatures in ranges of 19,000 °C–~4x the Sun’s temperature.

Question 10

What technology can produce higher temperature than electric arcs?

Pg 7

Answer 10

Only industrial lasers make higher temperatures than elctric sparks.

Question 11

For an arc flash, what clothing must be worn?

Pg 7

Answer 11

If arc flash is possibile, flame retardant clothing for such use must be worn.

Question 12

True or false?
An arc makes a flash of light that damage eyes/cause blindness

Pg 7

Answer 12

true

Question 13

True or false?
Arc flash incidents cannot vaporise parts of an electrical equipment.

Pg 7

Answer 13

false
Arc flash incidents can vaporise parts of an electrical equipment.

Question 14

If a solid is turned into a gas what may happen?

Pg 7

Answer 14

sublimation-If a solid is turned into gas, it expands enormously, a pressure wave that can reach 300 pounds per sq ft.

E.g. Copper expands by factor of 67,000.

Question 15

How strong can a sublimation be?

Pg 7

Answer 15

The shock wave can knock you across a room.

Question 16

A sublimation pressure wave can make sound levels of how much decibels?

Pg 7

Answer 16

Pressure waves make sound levels exceeding 160 dB.

• 100 dB: noise level of a chainsaw/loud rock concert
• 140–180 dB: a jet engine at takeoff, can be harmful to hearing
• 180 dB+: akin to a rocket launch/big explosion sound

Question 17

Can molten metal fly at high speed like a hand grenade explosion?

Pg 7

Answer 17

Yes, molten metal can fly at high speed like a hand grenade explosion.

Question 18

What are general characteristics of an arc flash?

Pg 7

Answer 18

• extreme heat
• strong flash of light
• powerful pressure waves
• powerful sound waves
• flying parts
• smoke and fumes

Question 19

When to work on live circuits?

Pg 7

Answer 19

Never work on live circuits.

This can be as simple as unplugging a lamp before you fix the switch.

Question 20

Why should you never work on live circuits?

Pg 7

Answer 20

It can involve many people, in different places and very complex procedures in the case of a high voltage transmission line.

Question 21

Pg 7