Electrical arc-flash risk treatment: comparing EU and US methods
17 October 2013
Author: Hugh O’Kelly BSc MPhil CEng FIEI FIET, engineering director, Premium Power Ltd
Among the risks associated with working on live electrical equipment, the issue of arc-flash hazard has emerged as a subject of increasing focus, firstly in the USA and more recently in Europe. This article outlines the background to arc-flash hazard assessment in both jurisdictions. It provides an overview of the relevant assessment procedures and how US standards should be considered in the context of EU, UK and Irish legislation.
During the years 2000 to 2010 inclusive, Health & Safety Authority (HSA) publications indicate that there were over 2,000 reported injuries and 26 deaths resulting from electrical accidents in the workplace in Ireland. It is a requirement under Safety, Health and Welfare Act 2005 (S.I. no. 10 of 2005) that “every employer shall ensure, so far as is reasonably practicable, the safety, health and welfare at work of his or her employees”. This clearly extends to working on electrical systems.
S.I.299 of 2007 Part 3 (Electricity) states that “it is preferable that work on or near electrical equipment should be carried out when that equipment is dead, but work on or near live conductors may be permitted in exceptional circumstances”. This standard also states that work on live equipment should not be undertaken unless:
- it is unreasonable in the circumstances for it to be dead;
- it is reasonable in the circumstances for such person to be at work on or near it while it is live; and
- suitable precautions are taken to prevent danger including, where necessary, the provision of protective equipment.
According to the Act, electrical hazards associated with electrical systems and equipment include burns sustained at the point of accidental electrical contact, or due to arcing from high-voltage conductors.
The question of ‘arcing’ and electrical-arc hazard in EU, UK and Irish legislation is addressed in the context of a risk assessment covering all risks associated with working on or near live electrical equipment.
An arc flash is an explosive release of energy that can result from an electrical short circuit that takes place between electrical conductors or between an electrical conductor and earth. During an arc flash, rapidly expanding air and superheated metal vapour are produced, which can cause serious injury including burning, blindness, loss of hearing, impact injury and even death.
According to research carried out by CapSchell Inc, a research company specialising in workplace accident prevention, there are between five and ten arc-flash explosions per day in the US.
ARC-FLASH RISK TREATMENT IN THE US
In the US in recent years, a more focused and quantified approach has been taken on the issue of electrical arc flash hazard, driven by the Occupational Safety and Health Administration (OSHA) and the National Fire Protection Association (NFPA) through its National Electrical Code (NEC).
NFPA standard 70E sets out a process for achieving electrically safe working conditions. The standard requires the employer to implement and document an overall electrical safety programme that directs activity appropriate for the electrical hazards, voltage, energy level and circuit conditions. A key recommendation is that, as far as possible, electrical conductors and circuit parts should be de-energised and have lockout/tagout devices applied.
The standard sets out in detail the procedure to be taken, as well as the labelling and worker training required. It also sets out the requirements for work involving electrical hazards where equipment cannot be de-energised and locked out. NFPA 70E sets out a number of boundaries from the live electrical conductors, arc flash boundary and shock protection.
Arc-flash boundary is defined as the boundary inside which a worker may be exposed to incident energy of more than 5 Joules/cm2 (1.2 cal/cm2). Levels above this are likely to cause second-degree burns, hence the value selected.
Shock protection boundaries specify distances from an energised electrical conductor. The shock boundary distances are affected by the voltage level and the types of equipment containing the conductors; e.g. exposed movable objects or exposed fixed object. These distances include limited, prohibited and restricted approach boundaries.
It is always recommended by the NFPA and best practice that workers follow de-energised and lockout/tagout safety procedures while working on electrical equipment. However, where workers need to work on live equipment, they must assess and address the associated hazards including the potential arc incident energy and be wearing the appropriate personal protective equipment (PPE). To this effect, the NFPA has developed an analysis technique based on IEEE1584. The calculated potential arc incident energy levels are categorized by number as set out in the table below.
IEEE states: “While the method does not exactly calculate incident energy levels and flash protection boundaries at the buses under consideration, it does allow for an accurate determination of required PPE levels and maximum flash-protection boundary distances.”
|‘Protective Clothing Characteristics’ adapted from Table 130.7(C)(11), NFPA 70E-2004|
|Hazard / Risk Category||Incident Energy Threshold (cal/cm2)||Clothing Description||No. Of Clothing Layers||Required Minimum Arc Rating of PPE|
|0||0||1.2*||Non-melting, flammable materials (i.e. untreated cotton, wool, rayon, or silk, or blends of these materials) with a fabric weight at least 4.5 oz/yd2||1||N/A|
|1||>1.2*||4||FR shirt and FR pants or FR overall||1||16.74||4|
|2||>4||8||Cotton underwear – conventional short sleeve and brief/shorts, plus FR shirt and FR pants||1 or 2||33.47||8|
|3||>8||25||Cotton underwear plus FR shirt and FR pants plus FR overall, or cotton underwear plus two FR overalls||2 or 3||104.6||25|
|4||>25||40||Cotton underwear plus FR shirt and FR pants plus multilayer flash suit||3 or more||167.36||40|
|x||>40||No Maximum||No PPE Specified in NFPA 70E|
|*NFPA 70E-2004 130.7(C)(5) states that “Employees shall wear FR clothing wherever there is a possible exposure to an electric arc flsh above the threshold incident-energy level for a second degree burn, 5 J/cm2 (1.2 cal/cm2).”|
ARC-FLASH RISK TREATMENT IN THE EU
In the European Union, the EU Workplace Health and Safety Directive (89/391/EEC) places an onus on employers to assess and address the occupational safety and health of people engaged in work or employment. For work on electrical equipment, this should include the hazards of electricity. The EU directive is translated into local legislation in the various country members, for instance in the UK under the Management of Health and Safety at Work 1999 and Electricity at Work Regulation 1989. The relevant regulation in Ireland are the Safety, Health and Welfare Act 2005 and S.I.299 of 2007 part 3 (Electricity).
Under EU directives, the emphasis is on risk analysis and on designing and ensuring safe working practices and methods. Risk assessment may, for instance, consider such issues as IP protection level (EN60529, 1992 – Degree of ingress protection). The EU standard EN60438-1 (form factor) may also be considered. Working space requirements may be considered as set up in EN50110-1, 1997.
Where it is unreasonable to switch out a piece of electrical equipment and live work must be undertaken, then the risk assessment must consider the question of arc flash hazard. This should include an assessment of the prospective incident energy level. The correct PPE appropriate to the task in hand should then be worn. The rating of the PPE should be greater than the calculated prospective incident energy.
The PPE should be CE marked and comply with the relevant IEC or EN standards. For arc flash clothing, this should be to IEC/EN 61482 part 1-1, 1-2 and 2. This standard defines two classes of garment, Class 1 and Class 2. Garments should be CE using EN340 and ISO 13688.
The wearing of the appropriate hand protection is particularly important because hands can be significantly more exposed than the torso. There are no EN standards currently developed for hand protection; however, the following standards, under development, are recommended:
- ASTM international standard draft of ‘test method for determination of the arc rating of gloves’, working group WK14928 item 2; and
- EN 61482-1-2 modified for the testing of gloves.
Similarly, for head protection there are no EN standards developed to provide an appropriate means of testing for headwear or face shields, to protect against the thermal hazards of an electric arc. However, the following test methods have been developed by DuPont for face shield testing: ASTM F 2178 – 08 Open Arc Test (Standard Test Method for Determining the Arc Rating of Face Protective Products) and GS-ET-29 Box Test (Supplementary Requirements for the Testing and Certification of Face Shields for Electrical Works). It is recommended that a specialist supplier is consulted when selecting and purchasing arc resistant PPE. DuPont has undertaken extensive research in this field and, manufactures a special fabric called NOMEX, which is used in arc flash PPE.
In Europe, a technical committee under CENELEC CLC TC 78 has recently been set up to define a method of calculating incident arc energy. It is expected that this will take several years to issue a report. In the meantime, general engineering opinion is that IEEE1584 is the best standard available for this purpose.
IDENTIFICATION, MARKING AND WARNING SIGNS
In the EU, the European Council Directive 92/58/EEC stipulates the minimum requirements for the provision of safety and health signs at work. This is designed to be visual and easily understood by all, for absolute clarity, in a continent with many languages. For this reason, the use of imported signage is prohibited by law.
The standard sign for electrical shock hazard is the lightning symbol shown in the danger triangle. Where other information need to be provided regarding the hazard, this should be shown on a separate notice.
The symbol and colouring scheme laid down in the European Council Directive must be adhered to. Signs must be clearly visible to all personnel entering a hazardous area. They should warn about any remaining risks. Signs may instruct employees about the measures to be takes in relation to these risks. Employees should fully understand the meaning of such safety signs and be made aware of the consequences of not following the warning or instruction given.
Companies wishing to address the risk/hazard associated with arc flash in the EC should be aware that NFPA70E is a US standard. However, while providing excellent information and guidelines, it does not apply under Irish law. Under the Irish standard SI299, the requirement of the employer is to carry out a risk assessment and develop an appropriate safety plan and this is spelt out in some detail. In the event of an accident requiring a HSA inspection, the assessment of compliance/culpability will be carried out according to Irish law based on EU directives.
In summary, engineers carrying out risk assessment for multinationals using NPFA70E need to bear in mind that in the EU, local safety legislation based on EU directives and standards takes precedence.http://www.engineersjournal.ie/2013/10/17/electrical-arc-flash-risk-treatment-comparing-eu-and-us-methods/http://www.engineersjournal.ie/wp-content/uploads/2013/10/Electic-1024x724.jpghttp://www.engineersjournal.ie/wp-content/uploads/2013/10/Electic-300x300.jpgElecelectricity,European Union,Ireland,legislation,safety