DGUV Information 203-078 - Thermal hazards from electric fault arc Guide to the ...

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Annex 2 , Standardisation of PPE against the thermal effects...
Annex 2
Thermal hazards from electric fault arc Guide to the selection of personal protective equipment for electrical work (bisher: BGI/GUV-I 5188 E)

Anhangteil

Titel: Thermal hazards from electric fault arc Guide to the selection of personal protective equipment for electrical work (bisher: BGI/GUV-I 5188 E)
Normgeber: Bund
Amtliche Abkürzung: DGUV Information 203-078
Gliederungs-Nr.: [keine Angabe]
Normtyp: Satzung

Annex 2 – Standardisation of PPE against the thermal effects of electric fault arcing

  1. A 2.1

    Standards for protective clothing in Europe

    The testing of PPE in Europe with respect to electric fault arcing is a comparatively young field. Contrary to testing the effectiveness of protective clothing and head, face or hand protection against a variety of other risks, the detailed investigation into the options for protecting against the thermal effects of an electric fault arc first began in the 1990s.

    Fig. 23
    Test setup, Box test method

    The standardisation process began with the initial desire to be able to safely and reproducibly test and evaluate that particular clothing used to protect against the effects of an electric fault arc. To this end, testing was begun in two classes based on the prENV 50354 draft standard existing at the time as to the protection provided by textile fabrics and products. This method already employed a box with one side open for generating a directed electric arc exposure at the textile fabric or product specimens positioned at a distance of 300 mm. This draft already defined the use of aluminium and copper electrodes, as well, in order to be as consistent as possible with real conditions.

    Assessment criteria was comprised of:

    • no specimen afterflame 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 its lack of goal orientation towards making a definitive statement as to the actual protective properties of PPE against the thermal effects of electric fault arcing. The method's intent was merely to confirm that, when tested clothing is in use used when a fault occurs, no clothing-related injurious effects (e. g. due to burnt clothing) are to be expected by the wearer. To that effect, the possibility for evaluating the risk of skin burn, as could be experienced if protective clothing with inadequate thermal insulation were used, was not included either.

    These safety-relevant gaps in the testing and evaluation of protective clothing against the thermal hazards associated with electric fault arcing were subsequently closed, however, with the drafting of the internationally harmonised standard VDE 0682-306-1-2. Consistent with the advancement of the idea of directed electric arc testing by means of a test box opened only in the direction of the specimen, this standard comprises the testing of fabrics and garments over two protection classes distinguished by respective levels of electric arc energy and incident energy.

    The table below provides an overview of the relevant parameters for each test category:

    Test
    category
    Mean value
    of electric
    arc energy
    W arc [kJ]
    Mean value
    of incident
    energy
    E io [kJ/m 2 ]
    Test
    current [kA]
    Arc time
    [ms]
    Class 11581354500
    Class 23184237500

    Table 8 Box test method parameters

    The basic philosophy of this methodology consists of objective testing and evaluation of the protection against electric fault arcs afforded by highly flame-resistant materials or material combinations, as well as testing of the protective properties of finished products. Both the fabrics specimens and garments are positioned at a distance of 300 mm 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 to each other. The electrode material is comprised of aluminium (upper) and copper (lower) in order to replicate system conditions as closely as possible in practice. The desired focusing of the extreme thermal effects associated with electric arc exposure is created with 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. In accordance with the testing current used for the respective test category, an arc flash is ignited in a 400 V AC test circuit and extinguished after a combustion duration of 500 ms.

    A test plate with two integrated calorimeters for measuring transmitted incident energy is used to mount the textile specimens. This enables measurement of the heat transfer to the skin surface (rear side of sample) and, in so doing, allows for conclusions to be drawn as to the risk of second degree burning in comparison to the limit values associated with the Stoll/Chianta criteria. In addition, a visual assessment is made of each specimen based on afterflame time, hole formation and melting through to the inside.

    Garments, such as jackets, overcoats, parkas, etc., are tested on a standardised mannequin. Besides the visual assessment criteria analogous to a surface inspection, an additional functional test is performed on the garment's closure system. This is required because only a functioning closure system enables the fastest possible removal of garments following 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 for protection against electric arcing within the territory covered by Europe's mandatory Directive 89/686/EEC relating to personal protective equipment.

  2. A 2.2

    Standards for protective clothing outside the EU

    Outside Europe, evaluation of electric fault arc protection is based primarily on one other test method.

    Determination of the ATPV (Arc Thermal Performance Value) arc rating according to IEC 61482-1-1 dominates the field. This methodology, also published as VDE 0682-306-1-1, calls fora medium voltage source and is based on three circularly arranged material specimens (120 offset) being exposed to an open, non-directional arc flash. The textile specimens are affixed to panels, on which two calorimeters are installed for measuring transmitted incident energy. In addition, each panel is 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, VDE 0682-306-1-1 does not specify defined classes of protection. The method determines variations in the arc duration from at least 20 individual values as well as a mathematical regression algorithm for each highly flame-resistant material for the respective arc rating (ATPV or EBT50). At the same time, the rating represents an energy impacting the material, which, with 50% probability, will not lead to second-degree skin burns (ATPV) or to a breaking up of the material down to the skin surface (EBT50).

    Assessment criteria for each individual test sample are:

    • Hole formation/breaking up of the material in all positions,

    • Heat transfer exceeding the limit values for skin burn (Stoll curve).

    After determining the rating for the material, product durability is tested using the same arc duration and mannequin mounting instead of panel mounting.

    In order to make a decision appropriate for the ATPV arc rating regarding the use of the clothing, the user of this method must be able to safely and successfully apply the results of a hazard or risk assessment, such as described in NFPA 70e or IEEE 1584. Otherwise, the rated value will not suffice for making a selection recommendation for work on or in the vicinity of electrical equipment. Similarly, there are no sure options to date for assessing the comparability between the ATPV value and the primary method used in Europe for testing and certifying protective clothing according to VDE 0682-306-1-2.

  3. A 2.3

    Standards for other types of PPE

    As opposed to protective clothing, there are neither precise internationally harmonised requirements nor testing or evaluation standards that address other means of effective bodily protection against electric fault arcing, such as face shields or gloves. Yet, a high burn risk still exists in the event of a fault, emphasizing all the more the necessity for appropriate personal protection. For this reason, efforts are being made to implement relevant procedures at both the national and the international levels.

    The common element among these efforts is that they are based, to the greatest extent possible, on existing international standards for protective clothing. A largely complete selection of protective equipment is available to the user today, whose electric fault arc protection properties have been tested and evaluated to the same basic principles.

  4. A.2.3.1

    Standards for Europe

    Electrician face shields are covered by the most comprehensive testing and evaluation procedures to date in the GS-ET-29 Principles of testing by the Electrical engineering testing and certification facility ETEM in DGUV Test. It defines supplemental requirements for the testing and certification of face shields for electrical work and has been in use since 2009 for all approved products in the Federal Republic of Germany.

    The Principles of testing use directed exposure with the Box test method analogous to that of VDE 0682-306-1-2 in both test categories for evaluation of thermal protection with respect to the effects of an electric fault arc. In contrast to the test of clothing, however, one test head outfitted with four calorimeters is used for positioning test specimens (e. g. a helmet in combination with visor). This is centred opposite to the electric arc axis, so that the central calorimeter is located at a distance of 350 mm from the nose area. The vertical position of this calorimeter is also centred at the middle of the electric arc axis. This guarantees the central impact of the electric arc energy being at the centre of the visor while simultaneously measuring the transmitted incident energy at different positions around the head. Besides the calorimeter in the area of the nose, the test head is also outfitted with two additional calorimeters in the areas of the eyes and the chin. A 500 mm high and 600 mm wide torso plate is used to simulate the area of a human's upper body. By measuring the incident energy with calorimeters, an objective conclusion can be drawn as to the risk of facial skin burn associated with a frontal exposure, as well as with the suppression of flame and gas clouds. Electric arc testing of the face shield is considered to have been passed when four of the test specimens demonstrate an afterflame time ≤ 5 s, no melting through of the test objects and no appearance of hole formation. At the same time, the value pairs of all test head calorimeters must lie below the limit values according to the Stoll/Chianta criteria for the risk of skin burn. By testing electrician face shields in this manner, the user can assume to be in possession of a product proven to the current state of technology.

    At the international level, the existing standard IEC 60903 for electrically insulating protective gloves, currently under revision, is being considered for expansion to include the testing and evaluation of resistance to electric arcing and related protection afforded by gloves. It uses the basic system conditions for directed exposure with the Box test method according to VDE 0682-306-1-2 while using specimen holders designed especially for gloves. Two side-by-side configured panels, each of which being outfitted with horizontally and vertically oriented calorimeters centred at the middle of the electric arc axis, enable testing of complete gloves. In addition to testing programs for Classes 1 and 2 related to clothing, a program for Class 3 is also possible. It serves the evaluation of products exposed to significantly higher direct incident energy (760 kj/m2), which appears justifiable for gloves, if only because of their anticipated close proximity to a potential fault source. The additional class ratting is achieved by reducing the distance between the specimen and the electric arc by 50 % (150 instead of 300 mm) while using the respective Class 1 electric arc energy (158 kJ). This application is not limited to electrically insulating protective gloves but, for this reason, can also provide important safety-related information about other glove types, such as those made of leather. Procedures call for the testing of at least four gloves, none of which may exhibit an afterflame time > 5 s, hole formation, melting through to the inside or material shrinkage > 5 %, nor may they exceed the limit values for skin burn corresponding to Stoll/Chianta criteria. Under these conditions, the user can assume the protective gloves have been tested and evaluated according to latest and best knowledge available.

  5. A.2.3.2

    Standards outside the EU

    Testing and evaluation options are also available for clothing articles used as supplemental protective equipment, which have been tested according to the ATPV arc rating described in IEC 61482-1-1.

    Head and face protection can be tested according to the ASTM F2178-08 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 head outfitted with four calorimeters. This is then attached to a mannequin, similar to those used for durability testing for clothing. The central calorimeter is horizontally and vertically centred opposite the electric arc axis in the facial area of the head, analogous to the Box test method. Direct incident energy and transmitted incident energy are determined for each test cycle by means of unprotected calorimeters positioned on the sides of the head, allowing for an incremental calculation of the ATPV arc rating.

    A U.S. draft standard 6) for gloves is under discussion, whereby systems engineering for clothing would be used to enable a determination of the ATPV arc rating for protective gloves. For this purpose, a ring-shaped structure with a quarter-circle opening has been designed 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 each unprotected calorimeters arranged on the sides of the panels serve to determine direct incident energy for each individual test cycle, as is done with textile testing. Determination of the ATPV arc rating then takes place analogous to the methodology already described.

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

  6. A 2.4

    Specification standards for product approval and selection

    Garments used for protection against electric arcing are high-tech textile products, often offering multifunctional protection. For this reason, the execution of a suitable electric fault arc durability test when selecting such clothing is not only sufficient in itself. Much more, it must be recognised and kept in mind that not one of the methods described to date is capable of reproducing the demands to which such PPE would be subjected.

    All of the standards mentioned to this point are merely test standards, which may confirm the most essential, but still not all characteristics related to safe clothing. In an emergency situation, for example, an inner lining made of non-flame-resistant material or a seam made of 100% polyester thread can cause significant serious injury to the wearer. Likewise, when too little current flow resistance is present, such as when surface conducting fibres are used to enhance clothing electrostatic dissipation capabilities, the protection against contact with live parts under certain circumstances may be lacking and further secondary hazards may ensue.

    Moreover, the classic textile requirements, such as dimensional stability when washing, maximum firmness and resistance to tear propagation, are, of course, not only quality-relevant to the user, but safety-relevant as well. Ultimately, only the use of suitable and appropriately tested accessories, such as flame-resistant reflective strips, logos or emblems, will avoid negatively influencing a clothing article's protective function. In order to achieve a degree of safety for the potential clothing user, both the manufacturer and the responsible certification body must have considered these risks and, by requiring suitable materials and appropriate design, eliminated them to the greatest extent possible.

    The international standard, IEC 61482-2, is presently regarded to be the best method for comprehensively testing and evaluating clothing used for protection against electric arcing. Even though a presumption of conformity to the PPE Directive 89/686/EEC does not exist yet for this standard, it provides the most extensive assessment options at the present time.

    An essential component of this product standard is the verification of electric fault arc protection properties through use of textile materials, as could be provided for according to VDE 0682-306-1-2. A decisive basic requirement is the exclusive use of flame-resistant raw materials (Index 3 according to DIN EN ISO 14116) for the outer and, if applicable, for the inner clothing layers. Typical demands for protective clothing placed on dimensional stability and mechanical wear durability, as well as on minimum requirements for maximum tensile strength and tear propagation resistance, supplement the material-specific requirement profile.

    IEC 61482-2 also regulates important safety-relevant requirements related to the clothing design itself. The subject of different protection classes for the front and back sides, perhaps selected for wear comfort, is also clearly regulated along 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, the user is assured of comprehensively tested and proved 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 suit. Even though none of the methods presented provides for the testing of products as assembled parts, the certification body will subject these products to an intensive assessment as to 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 will be decisive. If, in the results of a risk assessment, the use of a complete protective suit or overalls has been dispensed with, then the acceptability of pants selected separately from the arc rated jacket must be tested by the user himself. In order to avoid related uncertainties and perhaps risks, as the case may be, it is recommended to choose a complete suit made up of a jacket and pants.

    A European-wide, uniform methodology for the approval of clothing used for protection against electric arcing can not yet be expected because of the still outstanding, partial or complete conveyance of IEC 61482-2 into a generally compulsory harmonised EN standard (meaning an EN standard with presumption of conformity to the PPE directives), as well as the different potential experience levels of the certifying bodies. For this reason, employers should ensure that the requirements of this product standard have been taken into account and implemented into the product, accordingly, through an inspection of the certificate (EC type examination certificate), a thorough examination of the clothing, as well as a direct enquiry by the manufacturer or dealer.

6)

Work Item ASTM WK14928 - New Test Method for Test Method for Determining the Arc Rating of Gloves 1.