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By Paul Hopton – Principal Consultant Website: elecsafety.co.uk
Tel: 0800 652 1124
Introduction
Electrical Safety (UK) has helped many companies review and improve their Electrical Safety Management System (ESMS).
One question we are often asked is, what should an ESMS contain? This has prompted me to write a series of articles looking at the different aspects of these vital documents. Here is the third article in that series.
In my first article, we looked at your Electrical Safety Policy as the foundation stone for your ESMS; we then looked at your Electrical Safety Rules. This article looks at Arc Flash Hazard and risk assessment.
Introduction
Your Arc Flash instruction sets out practical requirements for managing arc flash risk. An arc flash is a rapid release of energy generally due to an arcing fault between a phase conductor and another phase conductor, a neutral conductor or earth. An arc flash happens when an electric current flows through the air between two conductive parts. Arc faults are generally limited to systems where the voltage is more than 120 Volts AC or 50 Volts DC. Most arc flashes are related to work activities on electrical systems.
The principles behind reducing arc flash risk to an acceptable level are understood and should be applied across your organisation. The main hazard associated with arc flash events is heat, up to 20,000°C, which can cause burn-type injuries. The other risks associated with arc flash events are a blast (and associated debris), ultraviolet light, sound waves, hot plasma, molten metal, and infrared radiation.
Legal & Mandatory Compliance
It is commonly understood that specific regulations identify the need to carry out a suitable and sufficient risk assessment and to put measures in place to protect those who could be put at risk is mandated. The Electricity at Work Regulations 1989 and The Management of Health and Safety at Work Regulations 1999 are specific in these areas.
From the Health and Safety Executive’s website under the topic heading of “Electrical safety”:
What are the hazards?
The main hazards of working with electricity are:
- electric shock and burns from contact with live parts
- injury from exposure to arcing, fire from faulty electrical equipment or installations
- explosion caused by unsuitable electrical Apparatus or static electricity igniting flammable vapours or dust, for example, in a spray paint booth
Electric shocks can also lead to other types of injury, for example, by causing a fall from ladders or scaffolds etc.
What do I have to do?
You must ensure an assessment has been made of any electrical hazards, which covers:
- who could be harmed by them
- how the level of risk has been established
- the precautions taken to control that risk
The risk assessment should consider the type of electrical equipment used, the way it is used and the environment it is used in.
Standards
EN 50110 Operation of electrical installations is the most relevant European standard when considering arc flash risk, but it does not currently provide much guidance. Future versions are planned and likely to offer more arc flash risk management advice. There is also an IEC Arc Flash Working Group (TC 78 WG 15), so an IEC Standard may be close.
The American IEEE 1584: 2018 Guide for Performing Arc-Flash Hazard Calculations and the American NFPA 70E® 2021 Standard for Electrical Safety in the Workplace provide the best guidance on risk assessment for arc flash hazard as follows:
- hazard assessment (arc flash hazard analysis)
- risk reduction measures implementation
- PPE is required where risk cannot be reduced through other means
Arc Flash Personal Protective Equipment is covered in IEC 61482-2:2018 Protective clothing against the thermal hazards of an Electric Arc and IEC 61482-1-1/2: 2014 Testing of Protective Clothing Standard.
General Approach
Specify the software tool used to model the electrical systems; EasyPower, ERACS, SKM or ETAP software could be used.
Carry out the discovery phase of the work, gathering information on the distribution system from documentation such as Design Documentation, Protection Records, Cable Schedules, Fixed Wiring Inspection and Test Reports, Single Line Diagrams etc. Data collection on physical assets is usually required. Typically, 95% of what you need can be collected from non-invasive inspection of equipment such as cables, switchboards, switchgear, protection relays, transformers, panel boards, fuses, circuit breakers and distribution boards. Consider how far down the network you will need to model, do not make the mistake of thinking that the risk will be higher at high voltage (above 1000Vac). Most typical industrial and commercial networks have higher risks at low voltage (below 1000Vac).
Once you have collected the data, you can start to build the distribution model in your chosen software package. When the model is complete, carry out short circuit; co-ordination; & arc flash studies. Any instances where the 3-phase prospective short circuit current exceeds the breaking capacity of protective devices or enclosures need to be remediated, as do cases of miscoordination. Incident energy levels and arc flash boundary distances are calculated during the arc flash study for all equipment within the study’s scope.
Where you have instances of high incident energy on individual pieces of equipment, an additional analysis should be carried out to determine if the incident energy could reasonably be reduced. The high incident energy level remediation work should be carried out. If you still have high incident energy levels on some of the equipment, consider carrying out task-based risk assessments to determine what tasks could expose personnel to arc flash and what control measures you can put in place to mitigate the risk. Finally, consider whether you will need to wear arc flash personal protective equipment (PPE) for the activities you will be carrying out and what level of protection that PPE will need to provide you with.
Arc flash warning labels should be produced and applied to the appropriate equipment.
Employees exposed to arc flash hazards should be given arc flash awareness and risk assessment training, including your requirements for mitigating arc flash risk.
Visitors to your site that could be exposed to arc flash hazards should be instructed on your requirements for mitigating arc flash risk. Electrical contractors, for example, should be informed of your arc flash PPE policy and what PPE they should provide for their employees to meet your requirements.
Finally, consider how often you will need to review your arc flash study and risk assessments to keep them current and relevant.
