Overcoming Arc Flash Hazards

Published 30 Jul 2019

Overcoming Arc Flash Hazards

Overcoming Arc Flash Hazards

Arc Flash Hazards

  • Blog Written By Patrick Mynett 
  • CEO / High Voltage Specialist at HV Training and Consulting Pty Ltd
    
    "Every worker can go home at night after a day at work"
    

Thorne & Derrick International would like to thank Pat Mynett for allowing us to publish his article Overcoming Arc Flash Hazards.

Pat is CEO at HV Training and Consulting Pty Ltd and is a High Voltage Specialist.

In 2014, Pat Mynett decided there was room in the market for another RTO to provide quality electrical training. Especially from a person with recent industry experience, whose main interest was in the electrical safety of workers and the welfare of the plant. Arc flash safety training was a glaring omission in the industry so he developed, wrote and registered a nationally accredited arc flash course for those who work in an arc flash hazard zone.

This is Part 3 in a series of articles about the dangers of arc flash – over the course of these articles we have discussed the definitions, dangers, statistics, causes, prevention and protection against arc flash.

  1. Introduction to Arc Flash
  2. Arc Flash – The Electrician’s Insidious Companion
  3. Overcoming Arc Flash Hazards

Arc Flash

Dangers

An arc flash can cause minor injuries, third degree burns and potential death as well as other injuries including blindness, hearing loss, nerve damage and cardiac arrest. Fatal burns can occur when the victim is several feet from the arc. Serious burns are common at a distance of 10 feet – arc flash can generate heat 4 times greater than the surface of the sun.

Arc Flash

The Energy In An Uncontrolled Arc Flash

Arc Flash is the result of a breakdown in insulation which in turn causes an excessive flow of current between phase and earth, phase to neural or phase to phase. This current flow may be thousands of amps, that is why arc flash fault current is measured in kilo Amperes (kA).

The energy released from an arc flash is governed by the systems voltage, the generation capacity available, the impedance to the source and the time the fault is on the system.

Arc flash is made up of molten metal, plasma, intense heat, intense light, gas, intense sound, and pressure waves, all released in milliseconds.

Arc Flash Energy In Perspective

To get some idea of the energy that can be released: a 415 volts system with 5000 amps/ 5kA of fault current flowing for 500 milliseconds or 2500 amps/2.5kA flowing for 1 second, it would have a similar energy release as one stick of explosive.

A 200kVA transformer’s fault current at the 415-volt terminals can be up to 6170 amps.

A 100kVA transformer’s fault current at the 415-volt terminals can be up to 3085 amps.

Both having the capacity to produce the energy shown in the paragraph above.

How Is The Energy From An Arc Flash Measured?

Firstly, the energy at the arc flash source, is different from the energy received from an arc flash. It all depends on where you stand. So, the energy received depends on the distance to the arc flash source.

The energy received from the arc flash is called Incident Energy.

It is measured in calories per centimetre squared, (cal/cm2).

Incident Energy is: The amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event.

So What Actions Can Initiate An Arc Flash

You will notice that all of the below, are actions that happen very frequently but only a very few ever initiate an arc flash. They are not normally the cause, there is usually other contributing factors,

1: Opening or closing a circuit breaker
2: Racking a circuit breaker in or out (see picture below)
3: Working live
4: Opening or closing a switch
5: Opening or closing an isolator
6: Dropping tools
7: Testing
8: Replacing parts

Arc Flash

What Initiates & What Causes An Arc Flash

Are Different In Many Cases

Because the initiating actions, are actions that are all part of normal operations carried out frequently by many electrical workers, very little thought is given to the action itself.

Just as an example:  A circuit has been modified. (AS/NZS 3000 specifies the circuit must be tested before re-energisation) yet many ignore this testing. The circuit breaker is closed without thought and there is a fault with the modification. The closing of the circuit breaker initiates an arc flash at the modification. If the circuit breaker has not been maintained, it may not clear the fault as per the trip settings time, it may not clear the fault at all, or another arc flash may occur at the circuit breaker.

Initiation Causes

1: Closing a circuit breaker – Closing onto a short circuit, the circuit breaker is under rated

2: Racking a circuit breaker in – Racking in a closed-circuit breaker onto a load

3: Closing a switch – Closing onto a short circuit and the upstream protection is incorrect

4: Opening an isolator – Opening an isolator with load on the circuit

5: Dropping tools – Working in a live switchboard with uninsulated tools

6: Testing using a non-rated multimeter with the settings on the wrong function

7: Replacing parts – Long tails make contact with live parts

8: Working live ignoring legislation, such as peer pressure not to turn the supply off

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Causes Can Often Be Traced To Human Performance

Let’s look at some human performance issues.

Not concentrating, “I’ve always done it this way,” rushing to finish the job, taking short cuts, ignoring standard procedures, lack of knowledge etc.

One of the biggest issues with arc flash, is the lack of knowledge. Most electrical workers have heard of arc flash and have some idea of the results but have little understanding of arc flash hazards and mitigation of the hazards.

A few years ago, it was taken as an occupational hazard that electrical workers would occasionally get injured or die from exposure to an arc flash. This should not be the case today as arc flash is now a recognised foreseeable occupational hazard.

Where Do We Stand Under Law?

Australian Health and Safety law is quite specific about occupational hazards.

Australian Model Work Health and Safety Regulations: Chapter 3 General Risk and Workplace Management

34 Duty to identify hazards

A duty holder, in managing risks to health and safety, must identify reasonably foreseeable hazards that could give rise to risks to health and safety.

35 Managing risks to health and safety

A duty holder, in managing risks to health and safety, must:

(a) eliminate risks to health and safety so far as is reasonably practicable; and

(b) if it is not reasonably practicable to eliminate risks to health and safety—minimise those risks so far as is reasonably practicable.

As arc flash is now a foreseeable occupational hazard, so there is a duty to manage these hazards. Yet many companies choose to either ignore or play lip service to arc flash hazards.

Understanding Arc Flash Comes From Quality Training

Training workers is one area where little is happening.

Some large companies consider a familiarisation session of one hour as adequate training.

To cover training adequately takes 5 to 7 hours to cover what is required. Training should include; what arc flash is, Legislation & Standards, definitions, incident energy, causes of arc flash, PPE selection and requirements, arc flash risk management.

Protect Yourself Against Arc Flash

Arc flash protection is provided by specialist clothing and garments for “head-to-toe” protection.

Enhanced and effective arc flash protection is safely achieved by wearing layers of protective clothing and garments manufactured from inherent fibres and which feature specific Arc Flash resilient components. Without the correct high-quality garments arc protection levels will be compromised.

Further Reading

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Further Reading