Electrical arc flash

When you woke up this morning you thought this would be a day like any other.

You've been called in to do a quick job, change a circuit breaker. No big deal. You've done it a million times before. You aren't going to rock the boat by asking for the power to be shut down. You'll just do it live. It'll only take a second.

What you don't know is in the six months since this panel was last opened, dust has built up between live parts. There's a loose screw waiting to drop at any minute, and the insulation on the bus bar is old, worn and about to crack.

But that doesn't matter. Whatever the reason, you're working on live, energised equipment and this is about to happen.

[Large explosion]

[High pitched tone]

So what just happened, you just experienced an arc flash. An unexpected, violent electrical short circuit where current flowed between the phase conductors, neutral and Earth. When that electrical arc fault occurred, the following things happened.

The arc caused a superheated ball of flame to erupt around you. A fireball that reached 20,000 degrees Celsius in a fraction of a second. That's four times hotter than the surface of the Sun. And it happened 30 centimetres from your face.

The copper conductors vaporised and expanded up to 67,000 times their original volume, culminating in a shower of molten metal flying directly at you.

The vaporised metals, smoke and burnt components formed a boiling, poisonous gas that engulfed you and went into your airways.

The pressure wave knocked you off your feet and into the wall behind you. Collapsing your left lung.

Thankfully, you survived.

Your hands took the bulk of the heat blast, causing third degree burns. You'll need skin grafts and months of rehabilitation. If you had worn the correct protective gloves, you could have reduced the risks and avoided serious burns.

Your front and back were badly burnt, with second degree burns across your chest from the initial blast, as well as a patchwork of first and second degree burns where your shirt caught fire. If you had been wearing the correct arc-rated protective clothing, it could have prevented the arc flash from setting your clothes on fire.

None of this would have happened if you had assessed the risks and deenergised the switchboard before you started work.

But it's too late now.

You will never regain the full use of your hands, so you may not be able to work as an electrician again. You'll be off work of any sort for months. On top of the injuries and lost wages, you'll also have fines to pay.

If there are energised parts; expect the unexpected and protect yourself against arc flash.

Always follow safe work procedures and wear appropriate PPE to reduce the risks of serious burns, injury or death.

Remember, the only way to eliminate the risk of arc flash is to choose not to work live.

Identify the electrical equipment with the potential for arc flash and any work in the vicinity of energised equipment.

Talk to your workers – they will have a good insight into the hazards they can see at your place of work.

The risk of arc flash increases by the degree of interaction with the energised equipment.

Consider the level of possible fault current present at the switchboard. Take into account:

• the physical size of the switchboard
• the size of the incoming consumer mains
• high fault current ratings of circuit protection devices
• the presence of fault current limiters on the switchboard
• transformers located near the switchboard.

You can use this risk assessment template (DOCX, 0.02 MB) to guide you and record your assessments.

A PCBU has a duty to either eliminate risks, if reasonably practicable, or to minimise them as much as possible. Workers have a duty to take reasonable care for their own health and safety.

You must work through the hierarchy of controls to choose the control that most effectively eliminates or minimises the risk of working near energised electrical parts. This may involve a single control measure or a combination of two or more different controls.

Under the hierarchy of controls, substitution, isolation and engineering controls are ranked at the same level of protection, ahead of administrative controls and then personal protective equipment.

A safe system of work or safe work method statement for managing the risk of arc flash should include:

• electrically isolating nearby electrical equipment or installation before starting work, and ensuring it can't be reconnected while the work is being carried out
• using insulated or non-conductive physical barriers to prevent inadvertent contact with energised parts
• ensuring workers have appropriate knowledge and skills to perform the work safely
• ensuring testing procedures are in place to prove parts are de-energised before work commences
• ensuring people not required for the work are excluded from the area, by use of screens, barriers and signage
• ensuring workers have tools, test equipment and PPE suitable for the rated level of fault current.

Additional consideration should be given to using a safety observer.

Control measures should be regularly reviewed. If necessary, revise your measures so they work as planned and are as effective as possible. The aim is to maintain a work environment that is without risks to health and safety.