I mentioned in Part1 about my first arc flash experience as a first- year tradesperson when testing using test lamps. The test lamps had large probes and I was testing on exposed terminals that
were close together and ‘bang’…..
I was extremely lucky to have escaped uninjured, other than my pride, but many others are not as lucky.
So, how could my incident and other arc flash incidents have been prevented by using more effective controls such as those higher up the hierarchy of controls?
SO FAR AS REASONABLY PRACTICABLE
Some might ask whether cost comes into the equation? Of course, it does! Section 35 of the harmonised Work Health and Safety Regulation requires duty holders, i.e. the Person Conducting the Business or Undertaking (PCBU), to manage health and safety risks by elimination so far as reasonably practicable. Section 18 of the harmonised WHS Act details that ‘so far as reasonably practicable’ means taking into account all relevant matters including “….the cost associated with available ways of eliminating or minimising the risk, including whether the cost is grossly disproportionate to the risk.”
The harmonised Work Health and Safety Regulation at Section 36 forces duty holders to use the hierarchy of controls (refer below), in combination with Section 35, to manage risks to health and safety from the top down.
Let us now look at the options in order of cheapest and simplest to the more expensive and extensive options to prevent arc flash incidents. The analysis for ‘So Far As Reasonably Practicable’ will depend on the situation.
LOW FAULT ENERGY TESTING TERMINALS
Test terminals could be provided to allow voltage checks/tests to be made safely. These would be best protected by HRC fuses with low fault current/energy let through. This a low-cost option that could be easily implemented where voltage measurements need to be regularly made or where measurements are likely to be needed.
A better option than the previous one would be to fit panel meters. A little more cost here but still relatively cheap compared to an arc flash incident. Again, this is an option where electrical measurements are regularly required to be taken.
METERS WITH REMOTE COMMS
Another option is to fit meters with remote comms. Additional cost to the previous option, but again this is an option where electrical measurements are regularly required, whether they be current, voltage or even the full gamut of power quality parameters.
PROTECTION SETTING ADJUSTMENT
A protection study could be carried out to ‘fine-tune’ the protection settings with a view to reducing the clearance times whilst still ensuring discrimination. Part of this should be to include labels for arc flash detailing the arc flash boundary, available incident energy and PPE requirements. The arc flash boundary is the boundary of second-degree burns.
Differential protection schemes and instantaneous trip settings help to reduce clearance times as well.
FAULT CURRENT LIMITATION
Current limiting protective devices that reduce the energy let- through provide an excellent risk mitigation measure. This is generally achieved at low voltage by using HRC fuses – many electrical people don’t realise that this is one of the primary roles of the low voltage service protective device. For my incident, this is the main reason I wasn’t severely injured i.e. the fuse blew very quickly.
ARC FLASH RELAYS WITH CHECK CT’S
Arc flash protection with point sensors, pressure sensors, arc flash protection relay with check current transformers (CTs) help ensure trip signalling in less than 1ms in some cases. The opening time of the circuit breaker still applies unless arc quenching protection is provided by a crowbar switch which are typically closed and the arc quenched within milliseconds.
Arc flash protection, such as that just described is likely to reduce the incident energy and arc flash ‘damage’ significantly.
FULLY INSULATED ARC CONTAINED SWITCHGEAR
Fully insulated and arc contained switchgear will also significantly reduce the risk.
I inspected a new switchboard a couple of years ago and the door wasn’t locked or the busbars insulated. Clearly the PCBU has not managed the arc flash or electric shock risk well, nor has the switchboard supplier and installer.
Qualifications and training for all those involved in the electrical process, from design to installation, maintenance, operating to removal and disposal, is ever so important.
Policies and procedures are also particularly important for all steps in the electrical process as mentioned – safe systems of work must be provided. Training and competency assessment in these safe systems is essential.
Permanently installed testing devices for proving de-energised so a person with a multimeter and test leads are not placed in a potentially dangerous situation. These testing devices are just starting to be accepted and used.
Remote switching devices can be temporarily installed on some makes of switches and circuit breakers. This and racking devices with remote control will help to remove the operator from the arc blast area.
Electrical equipment will need maintenance to reduce the risk into the future. Set and forget is not an option!
We have already discussed PPE in Part 1 and, yes, it has its place but there are a lot more options that are higher up the hierarchy of controls such as those mentioned.
Ok, we now know a lot of options to reduce the risk of arc flash but where do we start? A risk assessment will help to identify the arc flash risk and available control measures for all sites.
Establishing a program of works from this risk assessment is sensible. Quick and cost-effective wins are always good and then budgeting for the more costly options will be needed, keeping in mind what is ‘so far as reasonably practicable’ from the legislation. Options discarded because of this should be documented in the risk assessment process. A cost benefit analysis is part of this process.
One of my online students who has just completed our online Arc Flash course commented “More push to managers and supervisors and anyone racing toward KPIs as to how devastating a lack of funds spent on electrical can be.” Whilst this may be true in many workplaces, carry out the risk assessment, prioritise works based on the risk, the controls used will need to be costed out, the works program established and budgeting obtained to fund the works program. The program may take a few years to complete depending on the extent of the works, the expenditure and available funds, and resourcing issues.
There are numerous options that can be used to reduce the risk of arc flash. The WHS legislation forces duty holders to manage risks using the hierarchy of controls in this order: elimination, substitution, isolation (isolate the hazard and worker), engineering, administrative, and lastly PPE. PPE is on the bottom of the hierarchy of controls and so is least preferred. The other options mentioned in the paper are higher up the hierarchy of controls and therefore offer much better management of the arc flash hazard.
A risk assessment process is a great starting point with risks, controls and costs identified and prioritised. ‘So far as reasonably practical’ will help to determine what controls are finally implemented but we shouldn’t lose sight of what is to be achieved – workers going home at the end of the day in a healthy condition.