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Bridging the Protection Abyss

Published: 25th Feb 2014

In this paper, Hugh Hoagland and Zarheer Jooma discuss a new glove protection standard and conclude with advances by other international standard committees.

Introduction

If one subscribes to the Hominid theory, then the importance of standing on two limbs summarises the importance of using the other two limbs for advancing humanity. Hands are critical to perform day to day tasks.

In an electrical context, tasks from fault finding to switching are all performed by hand. The irony, prior to 2013, was that no standard had previously covered the arc rating of hand protection. A new standard published in 2013 has addressed this gap.

Hands and hazards

Electrical workers’ hands are exposed to many workplace hazards such as electrical shock, electrical arc flash burns, flash fires, cuts, splinters, oil, electrical solvents, pinching and crushing.

In the United States the National Fire Protection Association (NFPA) 70E - 20121 calls for the use of rubber insulating gloves with leather over protectors when shock protection is mandatory. The rubber insulating gloves aim to provide the shock protection itself, while the leather over protectors serve to reduce damage to the rubber gloves.

When it comes to arc flash protection, the standard requires that hand protection consisting of either leather or arc rated gloves must be worn. At the time of publication of the NFPA 70E - 20121, however, no standard addressing the arc rating of a glove existed. Instead it was merely implied that arc rated fabric could be used to produce a glove. Furthermore, the arc rating of the leather glove is not stipulated, but due to initial data presented from the new standard's development, a minimum thickness of 0.03 inches (0.7 mm) is required.

The use of the rubber insulating glove and leather over protector with the specified minimum thickness may have offered a definitive level of shock protection while addressing other hazards such as flash fires, splinters, minor pinches, and some level of cut and oil or solvent protection, but no published standard existed that allowed for the arc rating of the rubber and leather combination.

The American standard for insulating gloves, ASTM D1202, requires a Class 00 glove for work on systems rated 500 volts (V) or less. This insulating glove could be 0.02 inches (0.5 mm) with the leather over protector perhaps being 0.03 inches (0.7 mm).

Gloves generally become thicker as the voltage rises, as increasing the dielectric material offers increased ability to withstand higher voltages. The Institute of Electrical and Electronic Engineers’ (IEEE) 1584a3 guideline used to determine incident arc flash energies, however, states that fault current is the dominating contributor to energy and not system voltage. As an example, this would imply that it is theoretically possible to receive greater arc flash energy from a 480 V system than a 4.8 kilovolt (kV) system. From a shock perspective, however, the 480 V system glove is noticeably thinner than the 4.8 kV system glove. In other words, as the system voltage decreases the thickness of the rubber and leather glove combination decreases.

While this may imply a decreased arc rating, a decreasing system voltage may theoretically result in higher arc flash energies.

Historically, the incident arc flash energy could be calculated, but the arc rating of the glove was not stipulated on a rubber and leather combination. In certain cases, gloves were manufactured from arc rated fabric and thus assigned an arc rating value.

Such gloves offered arc protection, but may have failed to offer shock protection or cut resistance.

Another example would be cut resistant gloves. These gloves offer good finger dexterity and oil withstand, but may contain melting substrates. Some gloves may visually appear to be arc resistant until exposed to an arc4, at which point they will melt onto the user’s hands.

Legislation and standards

The United States' Occupational Safety and Health Standards (OSHA), 1910.138 (a) Subpart I: Addressing Hand Protection, states that “Employers shall select and require employees to use appropriate hand protection when employees' hands are exposed to hazards.” These hazards include severe cuts and lacerations, severe abrasions, punctures, thermal burns, and harmful temperature extremes.

When considering the correct selection of gloves, OSHA 1910.137(b)(2)(VII) states that “except for in a limited number of conditions, protector gloves must be worn over insulating gloves. The US OSHA has legally required protector gloves since 1991, but leather was not mandatory.

The original goal was mechanical protection, but in the past few years it has been realised that protector gloves often provide substantial arc flash protection.

Traditionally, legislation and standards stipulated the use of leather gloves with a minimum thickness or gloves manufactured from arc rated fabric. Arc rated fabrics are generally designed for minimal shrinkage, colourretention and comfort on skin. These characteristics, however, may not necessarily achieve the aims for cut resistance and grip.

Research and development in providing arc rated gloves that address arc flash in addition to other hazards did not progress as much as it had potential to, due to the absence of an arc rating standard for gloves. That changed in 2013, however, following the approval of an ASTM International standard ASTM F2675-13: Test Method for Determining Arc Ratings of Hand Protective Products Developed and Used for Electrical Arc Flash Protection5.

The standard has many benefits, with the most obvious being that the glove is tested as it would be used in the field. As discussed previously, gloves constructed from fabric tested on panels, using ASTM F19596 or International Electrotechnical Commission (IEC) 61482-1-17, are not the most comfortable and useable. The new standard now allows for knit, leather and other gloves to be tested for arc flash protection. Rubber gloves were not required to be arc rated, but most manufacturers opt to provide test data as this can be critical due to the ignition values of low voltage gloves in some colours. Specifying arc rated gloves will assure that the desired protection is achieved by a single glove or a layered arrangement.

Requirements and limitations

The ASTM F2675 standard does not provide any validation or results towards the shock protection performance of a glove, but this does not prevent dielectric or insulating gloves from being tested. In fact, a major benefit of the standard is the ability to now arc test products historically designed for shock.

Gloves constructed from fabric that complies with ASTM F15068 do not necessarily have to be retested, but testing may be beneficial to determine the performance as used in the field, since fabric tests are done on flat panels and glove design may enhance or diminish performance. The ASTM F2675 test is aimed more towards gloves that are not manufactured from flat panels and fabric that cannot be tested on a flat panel due to shrinkage.

Prior to arc testing, performance testing is required to ensure that the material does not melt or drip, that the after flame lasts less than two seconds and that the char length is less than six inches (150 mm). In the case of insulating gloves the standard requires ignition testing, since these gloves are not flame resistant in the traditional sense.

To ensure test replicability, only new size ten gloves qualify as test specimens. Subsequent usage in the field and exposure to contaminants may reduce the arc rating of the glove.

Used gloves may be tested for the purposes of field performance testing, or research and development, but not with the intention to offer an arc rating as the standard.

The arc generating rig setup is similar to that specified in ASTM F19596 and IEC 61482-1-17, except for changes to the glove product holders and sensor arrangement setup.

The testing rig consists of a glove holder and two monitor sensors on either side of the glove holder. The incident energy is the average of the two monitor sensors. A single sensor located on the glove holder provides measured energy through the glove. It is important that the glove rests snugly on the sensors and the test lab may use further means to ensure that satisfactory contact is made before testing.

Each glove holder and sensor is spaced 30 degrees apart. This theoretically implies that six glove holders and six monitor sensors may be present, but four test stands are recommended by the standard. A minimum of 20 data points are required by the standard.

Analysis is dependent on the Stoll curve performance to determine whether there is a burn or not.A minimum of 15% of the valid data points should result in a burn, while a minimum 15% should not. A valid mix zone consisting of at least 50% of the data points should be within 20% of the final arc rating.

Advancing technology

The biggest challenge facing industry in terms of hand protection is a glove that offers both arc flash and shock protection. This standard now opens the way for advancement in this area. Standards require that rubber gloves used for shock protection be worn with leather over protectors. Leather, however, has some weaknesses such as inferior cut resistance when compared with many other glove materials. It also has very poor chemical resistance.

Light chain hydrocarbons like hydraulic fluid and transformer oil or diesel fuel pass through leather almost instantaneously and are easily held in leather, allowing those gloves to ignite and burn quite readily.

This standard leads the way to using insulating gloves according to ASTM D1202, although composite over protectors offering arc flash protection, cut and chemical resistance, grip and finger dexterity are on the cards.

Conclusion

ASTM F2675-13: Test Method for Determining Arc Ratings of Hand Protective Products Developed and Used for Electrical Arc Flash Protection, is a new ASTM International standard published in 2013.

The now updated NFPA 70E-20121 Standard for Electrical Safety in the Workplace required arc flash leather gloves to be made of a certain thickness. Since the introduction of ASTM International’s standard, the gloves can now be made thinner and still meet minimum protection levels against the hazard.

Some leather gloves and gloves manufactured from fabric tested on flat panels were previously inadequate for multi threat hazards. Now, however, non leather speciality gloves that grip when wet or oily can be engineered to make the gloves more task specific and ergonomically designed. These gloves can now be arc rated, cut and chemical resistant, and offer shock protection.

More ergonomic gloves can be designed and tested for operations where no hazard exists.

Future developments

The ASTM F18 committee is now working on an additional option to allow OSHA-required (1910.137) protector gloves to be made of something other than leather. The 90 year old technology of combining rubber and leather gloves could be made a thing of the past by innovation spurred on by glove standards for cuts, punctures and arc flash. The future aim of protecting workers from shock and arc flash hazards while making gloves lighter, thinner and giving a better grip may not be as distant as once believed.

Numerous countries subscribe to the IEC standards. The former chair of the ASTM F18 taskgroup responsible for ASTM F26755 is also part of the IEC Technical Committee 78 Live Working subcommittee PT-78-13-1. This IEC committee is working on an arc rating standard for hand protection.

The latest feedback is that the last meeting in Sao Paulo, Brazil, towards the end of January 2014 resulted in a draft scope. This draft scope will be forwarded to the committee members who will start formalising a standard.

References

NFPA 70E – 2012 Standard for Electrical Safety in the Workplace, 2012. ASTM D120 Standard Specification for Rubber Insulating Gloves, 2006. IEEE 1584a – 2002 Guideline for Performing Arc Flash Calculations, 2002. Hoagland H, Shinn, B, 2012. ISHN Magazine: http://www.ishn.com/articles/92887-what-about-my-hands ASTM F2675-13, 'Test Method For Determining Arc Ratings of Hand Protective Products Developed and Used for Electrical Arc Flash Protection,' American Standard for Testing and Materials, West Conshohocken, Pennsylvania, Standard ASTM F2675 - 13, 2013.

ASTM F1959, 'Standard Test Method for Determining the Arc Rating of Materials for Clothing,' American Standard for Testing and Materials, West Conshohocken, Pennsylvania, Standard ASTM F1959, 2006.

IEC 61482-1-1, 'Live working – Protective clothing against the thermal hazards of an electric Part 1-1: Test methods – Method 1: Determination of the arc rating (ATPV or EBT50) of flame resistant materials for clothing' International Electrotechnical Commission, Geneva, Standard IEC 61482-1-1, 2009.

ASTM F1506, 'Standard Performance Specification for Flame Resistant Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards,' American Standard for Testing and Materials, West Conshohocken, Pennsylvania, Standard ASTM F1506, 2010.

Published: 25th Feb 2014 in Health and Safety Middle East

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