Importance of Arc Flash Hazard Analysis and Mitigation in New Zealand | Carelabs

New Zealand health and safety law does not tell you to eliminate every risk. It tells you to eliminate or minimise risk so far as is reasonably practicable, and that phrase is doing a great deal of work. Understanding what it requires is the clearest way to see why arc flash analysis matters here, because the test is almost impossible to satisfy for a hazard nobody has quantified.

What the test actually weighs

The Health and Safety at Work Act 2015 sets out what must be considered in deciding what is reasonably practicable. In substance it weighs:

• the likelihood of the hazard or risk occurring
• the degree of harm that might result
• what the person knows, or ought reasonably to know, about the hazard and about ways of eliminating or minimising it
• the availability and suitability of those ways
• and, after assessing those, whether the cost is grossly disproportionate to the risk

Read that sequence carefully, because the order matters. Cost is considered last, and only against the risk once the risk has been understood. You cannot reason about proportionality without a magnitude.

Why arc flash is difficult against this test

Take each element in turn for an unassessed switchboard.

Degree of harm. An arc event at an industrial switchboard can produce life-changing burns. That much is known generically. What is not known, absent a study, is whether a specific board presents two cal/cm² or sixty, and those are entirely different propositions requiring entirely different controls.

What you ought reasonably to know. This is the element that carries the most weight for arc flash, and it is the one most often overlooked. IEEE 1584 is a published, widely used international standard. Consultancies offering the calculation are readily available in New Zealand. The methodology is not obscure or emerging. It is therefore difficult to argue that a PCBU could not reasonably have known the incident energy at their equipment, because the means of finding out is neither exotic nor expensive.

Availability and suitability of controls. Maintenance switching, arc flash relays, setting changes and remote racking all exist and are commercially available. Their suitability, though, depends on the energy at the specific location — which returns again to the calculation.

Cost. Only assessable against a known risk. An unquantified hazard cannot support a proportionality argument in either direction.

The practical consequence is that "we did not know" is a weak position for arc flash specifically, in a way it might not be for a genuinely novel hazard.

The officer duty runs in parallel

Alongside the PCBU duty, officers carry a personal due diligence obligation, which includes taking reasonable steps to acquire and keep up to date knowledge of work health and safety matters, and to understand the hazards and risks of the operation.

For a business operating significant electrical infrastructure, an officer who cannot say whether arc flash energy has ever been assessed is exposed in a way that is uncomfortable to defend after an event. The study is not only an engineering deliverable; it is one of the few artefacts that evidences the duty was actively discharged.

Mitigation, and why the order is fixed

Once energy is known, controls follow the standard hierarchy, and the order is not a preference.

Elimination through de-energised work removes the hazard outright. Where a site insists on live work, the question worth asking is whether the constraint is genuine or simply inherited — an outage window that was never seriously scoped is not the same as a process that cannot stop.

Substitution and engineering controls reduce energy at source, and because incident energy scales roughly with arcing duration, every effective measure here attacks time: maintenance switching, optical arc flash relays detecting light rather than waiting for overcurrent grading, lowered instantaneous settings where discrimination permits, current-limiting devices, and zone selective interlocking.

Isolation of the person through remote racking and remote switching does not reduce energy but removes the exposure, which for racking operations is frequently the more practical answer.

Administrative controls — permits, procedures, boundaries — inform behaviour without changing the physics.

PPE is last. Arc-rated clothing addresses thermal energy only. It does nothing for the pressure wave, projectiles or acoustic injury, and above roughly 40 cal/cm² it stops being a credible control at all. A high calculated figure is an instruction to re-engineer, not a procurement specification.

Safe working practice under AS/NZS 4836 depends throughout on the hazard being understood, which is what the analysis supplies.

Keeping the position current

Controls decay quietly. A maintenance mode that is never engaged contributes nothing. An arc flash relay never tested is an assumption wearing the appearance of a control. Labels calculated against a fault level the lines company has since increased are wrong while looking authoritative.

The duty under HSWA is continuing rather than discharged once, so the assessment needs re-running whenever the source, the protection settings or the network configuration change.

Related reading: arc flash analysis in New Zealand covers how the study is carried out and what it delivers.