DGUV Information 203-077e - Thermal hazards due to electric fault arcing Guide for selecting Personal protective equipment

A 2.1
Standardization for protective clothing

The testing and evaluation of potentially life-saving clothing in the event of a hazardous incident is addressed in the standard, IEC 61482-2 [12], which establishes the requirements for protective clothing and materials used to protect against the thermal effects of electric fault arcing. This standard requires that testing must be performed on all clothing and materials under electric fault arc conditions. In addition, two normative testing methods have been specified at the international level.

A 2.2
Standards originating in Europe for testing protective clothing

The testing of PPEaA related to electric arcing began in Europe in the 1990s with an extensive examination of the potential protective properties of flame-resistant textiles against the thermal effects of electric fault arcing.

The standardization process was initiated with the goal of safely and reproducibly testing and evaluating the clothes used for protecting against the effects of electric arcing. Testing began with textile surfaces and products in two Arc protection classes on the basis of a draft standard available at the time: prENV 50354 [6] (Electrical arc test methods for material and garments used by workers at risk of exposure to electrical arcing), to determine the effectiveness of the protection provided. This method employed a box with one side open for generating a directed electric arc exposure at a test specimen, textile surface or jacket positioned at a distance of 300 mm.

This draft also defined the use of aluminium and copper electrodes in order to simulate real conditions as consistently as possible. The assessment criteria stipulated:

• no specimen after-flame time > 5 s

• no hole formation > 5 mm

• no melting through to the inside,

• functionality of the garment closure system following exposure.

The method's greatest disadvantage, however, was it lacked the goal of stipulating actual protection levels against the thermal effects of electric fault arcing. As can be seen from the assessment criteria, the methodology merely confirms that it is not anticipated that the bearer of the clothing will suffer injury due to its penetration during an electric arc occurrence (e.g. due to burning, hole formation, etc.). To that effect, it was also not possible to assess the risk of skin burn, as could be experienced if protective clothing with inadequate thermal insulation was worn.

Nevertheless, these safety-relevant gaps in the testing and evaluation of protective clothing against the thermal hazards associated with electric fault arcing were eventually filled with the internationally harmonized standard IEC 61482-1-2. This test standard was also published as DIN EN 61482-1-2 (VDE 0682-306-1-2) [11] and successfully revised for the first time in 2014. As a consequence of advancing the idea of directed electric arc testing using a test box opened only in the direction of the specimen, this standard comprises the testing of surface materials and products for two protection classes, distinguished by respective levels of electric arc energy and incident energy.

Table A 2-1 below provides an overview of the relevant parameters for each test category.

Fig. A 2-1
Test setup, Box test method

Table A 2-1 Box test method parameters

The basic philosophy of this methodology comprises the objective testing and evaluation of the protection afforded by flame-resistant materials or material combinations against electric fault arcing, as well as verification of the protection afforded by the finished product. Both the material specimens and products are positioned at a distance of 300mm to the electric arc axis, which corresponds to a conceivable working distance under realistic working conditions. The electric arc axis is defined by the two vertical electrodes positioned at a distance of 30 mm apart from each other. The electrode material is comprised of aluminium (upper) and copper (lower) in order to replicate practical system conditions as closely as possible. The desired focusing of the extreme thermal effects associated with electric arc exposure is realized through the parabolic form of the test box, which surrounds the electrode array on three sides. The upper and lower sections of the plaster box construction are sealed by means of insulating boards. Corresponding to the test current used for the respective Arc protection class, an arc flash is ignited in a 400 V AC test circuit and extinguished after a combustion duration of 500 ms.

The Box test method features a high degree of reproducibility. Within the context of revising the test standard, comparative testing was conducted and evaluated on the basis of ISO 5725-2, with the participation of four test laboratories in Italy, Spain and Germany. Standard deviations were determined for the material testing method, including the repeatability within a laboratory sr and the reproducibility s_R of the method (reproducibility or total deviation), depicted in Table A 2-2 below.

The parameters evaluated are the control variables for electric arc energy W_{arc, test} and direct incident energy E_i0P, as well as for the difference E_it - E_iSTOLL, which characterizes the quantitative test criterion for transmitted incident energy E_it (with relation to the threshold value E_iSTOLL for the onset of 2nd degree skin burns, accompanied by blistering of the skin with or without scarring).

For the reproducibility of the control variables, the standard deviation resulted in less than 5.3 % for electric arc energy and less than 11 % for incident energy, which is considered very good in light of the stochastics of the electric fault arc occurrence.

The Box test method setup utilizes a test plate for mounting the textile specimens, and on which two calorimeters are integrated for measuring transmitted incident energy. This enables measurement of the heat transfer to the skin surface (back side of sample) and, in so doing, allows for conclusions to be drawn as to the risk of 2nd degree burning with comparison to the limit values associated with the Stoll/Chianta criterion. In addition, a visual assessment is made of each specimen based on criteria related to after-flame time, hole formation and melting through to the inside. Finished products, such as jackets, overcoats, parkas, etc., are tested on a standardized mannequin. Besides the visual evaluation criteria analogous to a surface inspection, an additional functional test is performed on the garment closure system. This is required because only a functioning closure system enables the quickest possible removal of garments in the event of an electric arc accident. Moreover, testing the finished product also serves as a test of other accessories, such as reflective strips, logos or emblems with respect to their resistance to electric arcing.

This testing standard has been well-established for years and serves as the certification basis for numerous clothing articles used to protect against electric arcing within the territory covered by Europe's mandatory Regulation (EU) 2016/425 relating to personal protective equipment (previously Directive 89/686/EEC) [1].

Table A 2-2 Evaluation of the comparative test

New findings reveal that the Arc protection classes also describe the effects of energetic exposure in adequate DC systems.

A 2.3
Standards originating in America for testing protective clothing

Outside Europe, another test method is primarily used for assessment of arc flash protection. Determination of the arc rating ATPV (Arc Thermal Performance Value) in accordance with IEC 61482-1-1 is a dominant feature here. This methodology, also published as DIN EN 61482-1-1 (VDE 0682-306-1-1) [10], requires a medium voltage source and is based on an open, undirected electric arc with exposure of three material samples arranged respectively in a circular manner (120 ° offset). The textile specimens are affixed to panels, on which two calorimeters are installed for measuring transmitted incident energy.

Each panel is additionally outfitted with two unprotected calorimeters mounted on the left and right sides of the specimen, which simultaneously register the direct incident energy. The centre of the circle is formed by 2 stainless steel electrodes at a distance of 300 mm to each panel (electrode gap 300 mm). As opposed to the Box test method, IEC 61482-1-1 does not specify a defined class of protection. With a test current of 8 kA and variations in the arc duration, the method determines the respective arc rating (ATPV or EBT) for each flame-resistant material from at least 20 individual values using a logistical regression method. This rating represents the degree of energy acting on the material, which would lead to a 50 % probability of exceeding the Stoll threshold value (ATPV) or to a breakup of the material down to the body surface (EBT).

Fig. A 2-2
ATPV Test setup

Assessment criteria for each individual test sample are:

• hole formation/breakup of the material in all layers,

• heat transfer exceeding the threshold value for skin burn (Stoll curve).

After determining the rating for the material, the product is subjected to durability testing using the same arc duration and a mounted mannequin instead of panel mounting.

Users must be able to safely and successfully apply the risk assessment and risk estimation methodology in order to make the right choice of clothing appropriate for the arc rating. Otherwise, the rated value will not suffice for recommending a selection for work on or in the vicinity of electrical equipment. Examples for the risk asessment and risk estimation methodology can be found in NFPA 70E (Standard for Electrical Safety in the Workplace) [14] or IEEE 1584 (Guide for performing arc-flash hazard calculations) [15].

Similarly, there are no sure options to date for assessing the comparability between the ATPV value and the Box test method used primarily in Europe for testing and certifying protective clothing according to IEC 61482-1-2.

The methodology according to IEC 61482-1-1 was revised and appeared in a 2nd Edition in June 2019. In Germany, this standard was published as DIN EN 61482-1-1 (VDE 0682-306-1-1:2020-08) [10]. In addition to a multitude of technical clarifications and changes, the 2nd Edition is largely characterized by the introduction of a further parameter, ELIM (Energy limit). Besides the known values ATPV and EBT, this new parameter should solve the 50 % probability problem of exceeding the threshold value of thermal transmitted incident energy. This is realized in that the result only considers the average value of the three measured values directly beneath the transition range, designated as the mix zone.

Yet, the criteria for assessing the material using electric arc test shots, particularly with respect to the after-flame time and hole formation, is significantly different from the Box test method. For this reason, even the revised version of IEC 61482-1-1 does not include a limit for the after-flame time on materials that have ignited due to electric arc exposure. While the Box test sets clear limits on the maximum after-flame time of 5 s for material properties under evaluation and deemed critical, an equivalent determination is not found in IEC 61482-1-1. Even the definition of a hole (material breakup through all layers) at 25 mm is five times larger than in the Box test. This clearly shows the contrast between the European approach to testing and evaluation standards developed for legally stipulated PPE (according to the PPE Regulation) and the primarily American-dominated approach to electric arc testing and evaluation.

A 2.4
Standardization for other types of PPEaA

Experts from national and international standardization bodies are working to standardize further types of PPEaA, focusing particularly on protective equipment for the head, face, eyes and hands. The common element among these efforts is that they are largely based on existing, internationally standardized test specifications for protective clothing using the Box Test or the Open Arc Test. To a great extent, a complete selection of protective equipment is available to the user today, whose arc flash protection properties have been tested and evaluated according to the same basic principles.

A 2.4.1 Standards originating in Europe

A 2.4.1.1 Head, eye and face protection

The basic European standard for eye and face protection is EN 166. In Section 7.2.7 "Protection against electric arcing", however, the only requirements described therein have been derived from a series of tests where different materials are exposed to electric fault arcing and then visually inspected. It was presumed that PPEaA for the eyes and face that did not melt, burn or show any other signs of serious damage when exposed to electric fault arc testing, would also protect the wearer of this PPEaA. Yet, subsequent testing using sensors mounted behind the respective face shield revealed that this assumption was not justified. This is because, depending on the material and the design of the face shield components, and without additional testing, it cannot be ruled out that radiation could penetrate the optical component of the PPEaA for the eyes and face without causing relevant damage to the PPE itself, or that the arc energy could cause damage to the eyes or face from the side of, or from beneath the PPEaA.

For this reason. The Electrical engineering testing and certification facility in DGUV Test has developed the GS-ET-29 Principles of testing [23], which address all thermal-related hazards associated with electric fault arcing, as well as further occupational safety-relevant requirements, such as light transmittance. The test setup according to IEC 61482-1-2 was adopted for the electric fault arc testing described herein, using sensors set into a specially developed test head, two of which are at eye level, one at mouth level and one under the chin of the test head.

This test head is mounted onto a vertically arranged plate in such a manner that the mouth sensor is located at the height of the electric arc concentration.

The Supplemental requirements for the testing and certification of electrician face shields, integrated into these Principles of testing, have been mandatory for products certified in Europe since 2013 (refer to ‘Recommendation for Use' RfU ‘CNB/P/03.024' [13]). This ensures that, despite the prevailing absence of harmonized standards in Europe, certified products will have actually demonstrated both a resistance to, as well as protection against electric arcing.

Electric arc testing of the face shield is considered to have been passed when an after-flame time ≤ 5 s, no melting through of the test objects and no appearance of hole formation has been demonstrated on four test specimens. At the same time, the value pairs of all test head calorimeters must lie below the defined threshold values for the risk of skin burn according to the Stoll/Chianta criterion over the entire measuring period of 30 s.

EN 166 and its subordinate standards will be superseded in the near future by the international standards, ISO 16321-1, IS0 16321-2 and ISO 16321-3, which, however, no longer include specific requirements for protection against electric arcing. Nevertheless, parallel to these standards, IEC 62819 (VDE 0682-341) does comprise international requirements and testing standards specifically addressing the protection of the head, eyes and face against the thermal, optical and mechanical hazards associated with electric fault arcs. Besides the fundamental requirements therein, placed on all protective equipment for the eyes and face, special requirements will specify the thermal, optical and mechanical protective properties of PPEaA for the eyes and face while describing appropriate testing methods, or will reference the corresponding testing methods in accordance with ISO 16321-1 and IS0 16321-2.

Just as for eye and face protection the test standard GS-ET-29 [23] is the box test counterpart of the arc fault test standard IEC 61482-1-2, the North American test method ASTM F2178 [16] is the counterpart of IEC 61482-1-1 for determining ATPV, or EBT. Both methods are described in the international version of IEC 62819, but because of the 50 % probability of 2nd degree burns tolerated when determining the ATPV, it is likely that only ELIM, also described therein, will be used along with the Box test method in the harmonized EU version.

A 2.4.1.2 Hand protection

There is also an absence of harmonized standards for testing and evaluating protective gloves for resistance to, and protection against electric arcing. For this reason, the Department of Electrical engineering testing and certification facility, ETEM in DGUV Test has pursed the development of the Principles of testing GS-ET-42-1 "Supplemental requirements for the testing and certification of electrically insulating gloves with additional protection against the thermal effects of electric fault arcs" [24] and GS-ET-42-2 "Supplemental requirements for the testing and certification of heat-protective gloves used to protect against the thermal effects of electric fault arcs" [25] based on an earlier research project [27].

These test specifications have been available since February 2019 and comprise not only the testing of resistance to, and protection against electric arcing, but also further safety-relevant supplemental requirements for acceptable electric arc protective gloves. It uses the basic system conditions for directed exposure with the Box test method according to IEC 61482-1-2 while using specimen holders designed especially for gloves. Three semi-circular configured panels equal distance from the test box, each of which being outfitted with horizontally and vertically oriented calorimeters centred at the middle of the electric arc axis, facilitate testing of complete gloves.

Besides the testing of clothing for Arc protection classes APC 1 and APC 2, two additional tests for Arc protection classes APC 1_150 and APC 2_150 are possible. These contribute to the assessment of the product with a significantly higher degree of direct incident energy, which appears justifiable for gloves, if only on the basis of the anticipated short distance to the fault source. These additional test categories are achieved by reducing the distance between the specimen and the electric arc by 50 % (150 instead of 300 mm) while using the corresponding Arc protection classes APC 1 or APC 2 electric arc energy levels (168 or 320 kJ).

This application is not limited to electrically insulating gloves. GS-ET-42-2 also provides important safety-relevant information for other types of gloves, such as leather gloves. Yet, good thermal protection is important for effective PPEaA, which is why these gloves must fulfil the basic requirements of DIN EN 407 "Protective gloves against thermal risks (heat and/or fire)".

Not only is the burning behaviour of the material tested, but also the thermal stability of the seams with direct flame exposure (seam opening). With respect to arc flash protection, the test method calls for the testing at least three pairs of gloves (6 individual test objects). Subsequent to electric arc exposure, none of the specimens may exhibit an after-flame time > 5 s, melting through to the inside, hole formation or exceed the threshold values for skin burns according to the Stoll/Chianta criterion.

Under these conditions, one can assume the protective gloves have been tested and evaluated according to latest knowledge available.

At the end of 2018 on the basis of this work, it was resolved at an international level to form a project group for developing testing standards for all forms of protective equipment for hands (e.g. gloves, gauntlets, etc.) against the thermal hazards of electric fault arcing. Under the designation IEC 63232-1-2 [20], an international test standard based on the Box test will be published in the coming years, which will go beyond clothing and head, eye and face protection to encompass complete personal protection in the area of the hands.

A 2.4.2 Standards originating outside the EU

International non-harmonized test and evaluation options are also available for supplementary protective equipment for clothing tested according to ATPV arc rating described in IEC 61482-1-1.

Head and face protection can be tested according to the ASTM F2178 - 17b [17] standard, which was published only in the USA. This methodology uses systems engineering for determining the ATPV for textiles, whereby the test specimens, including helmet and visor, are affixed to a test head outfitted with four calorimeters. They are then attached to a mannequin similar to those used for durability testing of clothing, with the calorimeter, aligned horizontally and vertically centred opposite the middle of the electric arc axis, positioned in the facial area of the head. Analogous to the textile testing, measurements are made of the direct incident energy at the unprotected calorimeter on the side of the head for every test cycle. The arc rating is calculated step-by-step in conjunction with the measured transmitted incident energy.

The existing standard for testing and evaluation of gloves, published only in America, is ASTM F2675/ F2675M - 13 [18]. This concept calls for a ring-shaped setup with a quarter-circle opening, on which four panels are located for affixing the test specimen. Each glove panel is outfitted with a calorimeter, whose alignment is horizontally and vertically centred at the middle of the electric arc axis and is used for measuring the transmitted incident energy. Two unprotected calorimeters are arranged on the sides of the panels serve to determine direct incident energy for each individual test cycle, similar to the textile testing. Determination of the ATPV arc rating then takes place analogous to the methodology already described. The standardization work for the arc rating of equipment to protect hands (gloves, gauntlets, etc.) against the thermal hazards associated with electric fault arcing has been under way at the international level since the end of 2018 within the IEC 63232-1-1 project group [19].

Nevertheless, the same restrictions apply to the arc rating determined for face shields and gloves as for clothing. Its use requires experience in the application of American directives related to the assessment of electric fault arc risks at the workplace.

A 2.5
Requirements for proper selection

When considering satisfactory arc flash protection, one must always bear in mind the overall potential thermal risk to the head, the face and the torso, as well as the extremities out to the hands, generated by an arc flash. Even though international efforts have still not achieved the same standards for all these areas, the different types of PPEaA must always be viewed as an overall system when properly selected and matched to one another.

The outfits used for protection against electric arcing are high-tech products, oftentimes providing multifunctional protection. For this reason, respective electric arc resistance testing is not sufficient in itself when selecting such PPEaA. Much more, it must be recognized and kept in mind that not one of the methods described to date is capable of reproducing the overall demands to which such PPEaA would be subjected.

All of the standards mentioned to this point are merely test standards, which may confirm the most essential characteristics, but still not all those required of safe PPEaA. In an emergency situation, for example, an inner lining made of non-flame-resistant material or a seam made of 100 % polyester thread can severely injure the wearer. Likewise, with too little transmission resistance, such as when surface conductive fibres are used to enhance the clothing's electrostatic dissipation properties, the protection against contact with live parts may not exist under certain circumstances, and further secondary hazards may even arise. High concentrations of CO₂ can be detected in closed hoods without ventilation after only relatively short wearing periods, which, in turn, can impact concentration levels and could even lead to a loss of consciousness. The optical quality of the viewing panel on the visor and freedom of movement for the head must be considered. An unobstructed downward field of vision will prevent tripping, etc.

Moreover, the classic textile-specific requirements, such as dimensional stability when washing, maximum firmness and resistance to tear propagation are not only quality-relevant to the user, but safety-relevant as well. Finally, only the use of suitable and appropriately tested accessories, such as flame-resistant reflective strips, emblems or logos, will prevent any negative influence these might have on an article of clothing's protective function. In order to achieve a satisfactory degree of safety for the potential user, both the manufacturer and the responsible certification body must have taken these risks into account and eliminated them to the greatest extent possible by specifying suitable materials and appropriate designs.

The international standard, IEC 61482-2 [12] is presently regarded as providing the best method for comprehensively testing and evaluating clothing used for protection against electric arcing.

An essential component of this product standard is the verification of arc protection properties through the textile materials employed, as can be rendered in accordance with DIN EN 61482-1-2 (VDE 0682-306-1-2) [11].

A decisive basic requirement is the exclusive use of flame-resistant raw materials (Index 3 according to DIN EN ISO 14116 [5]) for the outer and, if applicable, for the inner clothing layers. The typical demands placed on protective clothing, emphasizing dimensional stability and mechanical wear durability, as well as the minimum requirements for maximum tensile strength and tear propagation resistance, supplement the material-specific requirement profile.

IEC 61482-2 [12] also regulates the important safety-relevant requirements related to design of the clothing, itself. Perhaps due to reasons of wearing comfort, different Arc protection classes selected for the front and back areas are also clearly regulated, such as with the exclusive use of flame-resistant sewing thread for all main seams. If special design requirements have been considered in addition to the standard, such as sealable pockets to protect against extensive molten metal splatter in case of fault, then the user can be assured of wearing comprehensively tested and evaluated clothing to protect against the thermal risks of an electric arc accident.

This also applies for the respective trousers or overalls as part of a complete protective outfit. Although the methods introduced were originally and are primarily intended for the testing of ready-made jackets, shirts, parkas and the like, the certifying bodies will also intensively evaluate pants for their protective properties. For this, the use of identical raw materials for pants and jackets, as well as the implementation of the design stipulations adopted in IEC 61482-2 [12] will be decisive. If, as a result of a risk assessment, the user determines that complete protective suit or overalls can be dispensed with, then the pants selected separately from the arc rated jacket must be tested for suitability by the user himself. In order to avoid uncertainties and possible risks, it is recommended to select a complete outfit made up of a jacket and pants.

Fig. A 2-3
Pictogram IEC 60417-6353 for marking electric arc tested PPEaA [Copyright © 2016 IEC Geneva, Switzerland. www.iec.ch] 1

Fig. A 2-4
Protective gloves identified with electric arc tested PPEaA markings

For especially hazardous areas with a very high degree of electric arc energy, or where an especially high level of wearing comfort is desired, clothing concepts that provide arc flash protection through a combination of multiple layers of clothing articles, such as jackets and shirts, may prove suitable. This "onion peel" principle derived from sports, recreation and outdoor activities, can also make a valuable contribution to the protection and safety afforded by PPEaA. Collaboration with a responsible and experienced supplier can lead to optimal design concepts that oftentimes provide significant added value when compared to the classic standard solutions. Essential requirements for this, however, are that the materials used for the individual parts of the clothing, as well as for the clothing articles, themselves, are suitably tested, are certified together and, of course, are worn.

It must be noted that the harmonized standard DIN EN 61482-2 will also be available shortly. In order to achieve this, the pending publication of the 2nd Edition of test standard DIN EN 61482-1-1must be realized (refer to A 2.2), because this standard includes the ELIM parameters for the first time. This will solve the problem of the 50% probability of exceeding the Stoll/Chianta criterion, which represents a prerequisite for the presumption of conformity in EN 61482-2 regarding PPE Regulation (EU) 2016/425. The standard EN 61482-2 came out in May 2020 and is based on IEC 61482-2: 2018 with the relevant modifications (IEC 61482-2:2018, modified).

For as comprehensive arc flash protection as possible, the user should also ensure that the manufacturer confirms compliance with IEC 61482-2 [12] and did not merely carry out testing on the material or the product. From May 2018, this must be made evident according to the 2nd Edition of IEC 61482-2 through a new Pictogram for PPEaA on the label (refer to Fig. A 2-3).

The same symbol can also be found on the marking (label) on electric arc protective gloves, which have been tested and certified according to GS-ET-42-1/-2. This gives the user the guarantee that these can be selected as an integral part of a holistic approach towards protection and can be used for their intended purpose.

The greatest challenge remaining is to define, and to choose the respective test category (Arc protection class APC 1, 2, 1_150 or 2_150), which the gloves will have to have passed. In this context, the user should not only consider the Arc protection class determined for the protective clothing (APC 1 or APC 2) when selecting PPEaA. Equal attention should also be placed on the risk-influencing ergonomic properties because, particularly with protective gloves in higher test categories, restrictions on the tactile attributes (agility) must be expected.

Fig. A 2-5
Head and face protection

Comprehensive arc flash protection is considered complete when tested and certified head and face protection is selected and worn in accordance with GS-ET-29 [23] (also refer to A 2.4.1.1). These products, as well, can be recognized by the electric arc tested PPEaA pictogram, which guarantees the wearer overall protection and safety from head to toe.