Electricity at Work Regulations 1989, UK wide
Arc Flash Risk Assessments
An arc flash releases the energy of a short circuit as heat, light, pressure and molten metal in a few thousandths of a second. AL23 Safety assesses arc flash risk against the Electricity at Work Regulations 1989 using the recognised international calculation methods, for clients UK wide. There is no UK arc flash standard to work to, which is precisely why the assessment has to be reasoned rather than bought off a shelf.
What is an arc flash risk assessment?
Working out how much energy could reach a person, then engineering that number down
An arc fault is a short circuit through air. The current flows through ionised gas rather than through a conductor. The energy that would have gone into the fault is released as radiant heat, blast pressure and vaporised metal. The measure used is incident energy, expressed in calories per square centimetre at a stated working distance from the arc.
The assessment establishes the prospective fault current at each point in the network, the clearing time of the device that will actually operate, the electrode configuration and the enclosure geometry. From those inputs it calculates incident energy and the boundary at which that energy falls below the level likely to cause a serious burn. The output is not a stack of labels. It is a set of decisions about which tasks may be carried out live at all.
Who needs one
Anyone whose people switch, test or work near energised equipment
- Operators of HV and LV switchrooms where switching, racking, testing or thermography happens on energised gear.
- Data centres and other concurrently maintainable estates, where uptime commitments push work towards live equipment.
- Utilities, generation sites, renewables and battery energy storage operators handling high fault level plant.
- Manufacturing and process sites with large LV distribution, close transformer coupling and correspondingly high fault currents.
- Battery rooms, UPS and DC plant, where a string cannot simply be switched off and isolation is by link removal.
- Contractors whose staff open panels on client sites without knowing the fault level behind the door.
The regulations that apply
Your legal framework, in plain terms
The Electricity at Work Regulations 1989 sit under the Health and Safety at Work etc. Act 1974 and carry the whole of the UK legal position on arc flash. There is no separate arc flash regulation. The Personal Protective Equipment at Work Regulations 1992, as amended in 2022, govern the clothing you select once the risk cannot be designed out. The Management of Health and Safety at Work Regulations 1999 require the assessment itself to be suitable and sufficient.
Regulation 4(3)
Work activities on or near an electrical system must be carried out in a manner that does not give rise to danger so far as is reasonably practicable.
Regulation 4(4)
Equipment provided for protecting people working on or near electrical equipment must be suitable for the use, maintained and properly used. This is where arc rated clothing sits.
Regulation 13
Where equipment has been made dead to allow work, adequate precautions must be taken to stop it becoming charged again while the work is going on.
Regulation 14
Nobody may work on or near a live conductor unless it is unreasonable for it to be dead, it is reasonable to work on it live and suitable precautions are taken to prevent injury. All three tests must be met.
MHSWR 1999, regulation 3
A suitable and sufficient assessment of the risk, recorded where you employ five or more people.
The honest bit about standards
There is no UK arc flash standard. There is no HSE endorsed calculation method and no British Standard that tells you how to compute incident energy. UK practice borrows from elsewhere. IEEE 1584 supplies the calculation model. NFPA 70E supplies the American work practice and PPE category framework. BS EN 61482 covers the testing and classification of arc rated protective clothing. The IET has published useful UK facing guidance on the hazard.
None of those documents is law in Great Britain. Anyone selling you compliance with NFPA 70E is selling you an American regime. What an inspector or a court will look at is whether you met regulations 4, 13 and 14. That means the study is only half the job. The other half is the evidence that you tried to work dead first, plus the record of why any remaining live task passes the regulation 14 tests.
What the assessment covers
From the network model to the label on the panel
- Network model built from the single line diagram, including transformer impedances, cable lengths and motor contribution.
- Prospective fault current at every assessed location, using the distribution network operator declared fault level at the supply point.
- Protective device identification, settings and actual clearing time at the calculated fault current rather than the nominal rating, cross-checked against your most recent fixed wire inspection.
- Incident energy calculated at each working position at a stated working distance, following the IEEE 1584 method.
- The arc flash boundary at each location, conventionally taken as the distance at which incident energy falls to 1.2 calories per square centimetre.
- Approach and restricted working distances for switching, racking, testing and inspection.
- Engineering options that cut incident energy at source, including protection setting changes, maintenance mode settings, zone interlocking, arc flash relays and remote racking.
- Task by task review of what is genuinely done live, tested against the three limbs of regulation 14.
- Arc rated clothing selection matched to the calculated energy, using garments classified to BS EN 61482.
- Labelling of assessed equipment with incident energy, boundary and the required protection level.
- The interface with your isolation and permit to work systems, which is where most incidents are actually prevented.
Our process
Calculate the energy, then engineer it down
- 01
Data collection
We gather the single line diagram, the network operator fault level statement, protective device schedules and settings, plus a list of the tasks actually carried out on live equipment.
- 02
Study and calculation
We model the network and calculate incident energy and boundaries at each assessed location, stating every assumption we had to make.
- 03
Design the energy down
Before anyone talks about clothing, we look at what reduces the number. Faster protection, differential schemes, maintenance settings and remote operation all beat a heavier coverall.
- 04
Boundaries, labels and PPE
We set boundaries, specify labelling and match arc rated clothing to the residual energy at each location.
- 05
Procedures and review
We rewrite the switching and isolation procedures around the findings, then set a review trigger for any change to protection settings, transformer capacity or the declared fault level.
What you get
A study that drives decisions, not just labels
- An arc flash study report giving incident energy, arc flash boundary and clearing time at each assessed location.
- A schedule of engineering measures that reduce incident energy, ranked by effect and cost.
- Equipment labelling content ready to apply, stating energy, boundary and required protection.
- An arc rated PPE matrix tied to locations and tasks rather than issued blanket across the site.
- Revised switching, isolation and live working procedures, with the regulation 14 justification recorded for each remaining live task.
- A clear statement of assumptions and limitations, including any location where the data was too poor to calculate reliably.
What we need from you
The network on paper and the truth about live work
- A current single line diagram. Where one does not exist, that becomes the first piece of work.
- The declared fault level at your supply point from the distribution network operator.
- Protective device schedules, types, ratings and current settings.
- Honest information about which tasks are done live today, including the ones nobody has written down.
- Switchroom access and a competent person to accompany the survey.
Why AL23 Safety
Engineering the risk down beats issuing heavier coveralls
Accountable
If your real problem is that people are working live when they do not need to, we will say that instead of selling you a labelling exercise.
Expert and chartered
We scope the study, appoint the right electrical engineering specialist, interpret the results and turn them into an action plan you can actually deliver.
Practical, not just compliant
Engineering measures come before clothing. Cutting a clearing time protects everyone who ever opens that panel, where PPE only protects the person wearing it correctly.
UK wide
We support arc flash work across the UK, from single switchrooms to utilities and energy estates and multi-site industrial portfolios.
Start with the work, not the labels
Tell us what your people actually do live
A short conversation about your switching tasks and your fault levels will tell us whether you need a full study or a tighter safe system of work. Both answers are legitimate and we will give you the honest one.
Common questions
Answers, up front
Cannot see your question? Get in touch and we will answer it directly.
Contact usNot by that name. No UK regulation mentions arc flash. The duties come from regulations 4, 13 and 14 of the Electricity at Work Regulations 1989 and from regulation 3 of the Management of Health and Safety at Work Regulations 1999. Where your people work on or near energised equipment, you cannot demonstrate suitable precautions without understanding the energy involved.
No. Both are American documents with no legal force in Great Britain. IEEE 1584 is nonetheless the calculation method in general use here. NFPA 70E is widely used as a work practice reference. We use them as recognised methods for discharging a UK duty. We do not present them as the duty.
It is the thermal energy that would land on a surface at a stated distance from the arc, measured in calories per square centimetre. The arc flash boundary is conventionally drawn where that figure falls to 1.2 calories per square centimetre, the widely used threshold for the onset of a second degree burn. Protective clothing is rated in the same units.
That is the common shortcut and it fails on regulation 14. Live working is only permissible where it is unreasonable for the conductor to be dead, where it is reasonable to work on it live and where suitable precautions are taken. Clothing addresses the third limb only. It does nothing about the first two. At high incident energy levels no practical garment is adequate.
It is as accurate as the data behind it. The two variables that move the answer most are the fault level and the protective device clearing time. A stale single line diagram or an undocumented protection setting will produce a confident number that is wrong. We state our assumptions and flag every location where the data was too weak to rely on.
Cost is driven by the number of assessed locations, whether a usable single line diagram exists and how much survey is needed to verify the network and the protection settings. Building a model from scratch is the expensive part. Send us a single line diagram and a board count and we will scope it properly.
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