The Arc Flash – we have all read the articles and listen to the numbers but do we really understand what the dynamics of these events are like and what potential dangers our electrical workers can encounter when working in and around energized equipment.
35,000 degrees that is the temperature that is created in the arc gap, three and a half times the surface temperature of the sun. In a controlled industrial application it is exactly the same as a plasma cutter used for cutting through large blocks of solid steel and other metals.
When you super heat air from an ambient air temperature of 75 degrees to 35,000 degrees in the blink of an eye, you create the same dynamics as a bomb. When a bomb explodes it is the rapid increase in heat that creates the expansive destructive forces that we are familiar with, So when we complete a HRC (Hazard Risk Analysis) and label our electrical equipment, all we are telling our electrician is how big a bomb he is standing in front of i.e. this is a CAT 1, 2, 3, or 4 bomb, that way he can dress appropriately with the proper PPE if the bomb were to go off.
In an Arc Flash like in a bomb, when it goes off –
You get thermal energy – that can easily ignite non – FR clothing
You get blinding white light – you can be temporarily blinded
You get noise – you are temporarily deaf
You get a pressure wave (concussive force) that can be 2200 lbs/sq/ft – it can collapse a lung, cause internal and soft tissue damage
You get molten metal, shrapnel traveling at 750 mph at 1900 degrees
All this is happening in a blink of an eye so without proper PPE your blinded temporarily, deaf temporarily, disoriented and being showered with molten metal and your clothing catches fire.
OSHA’s Final Rule on Electrical Protective Equipment (OSHA 1910.269) prohibits clothing that, when exposed to flames or arcs, could increase the extent of wearer injury. Employers must determine appropriate clothing based on an evaluation of potential hazards in the work environment. Clothing made from flame-resistant materials is acceptable under the Rule, i.e., clothing that meets the requirements of ASTM F1506. Untreated cotton or wool fabrics weighing at least 11.0 oz. or heavier untreated cotton or wool fabrics are acceptable under limited conditions identified by OSHA. (1.)
(1.) Arc conditions in the Duke Power Company videotape, which was the primary basis for OSHA’s determination, were a 3800 ampere, 12 inch (approx) electric arc that was approximately 12 inches from the material. The arc lasted for 10 cycles or 0.167 seconds.
The National Electrical Safety Code (NESC®) is published by the IEEE. It sets the ground rules for practical safeguarding of persons during the installation, operation, or maintenance of electric supply and communication lines and associated equipment.
The NESC requires that the employer determine potential exposure to an electric arc for employees who work on or near energized parts or equipment operating at 50 volts or greater. If the exposure is greater than 2 cal/cm
2, employees are required to wear clothing with an arc rating not less than the anticipated level of arc energy as determined by completing a detailed arc hazard analysis or by using tabulated values found in table 410-1. Table 410-1 outlines equipment types, nominal voltage ranges and the arc thermal performance value (ATPV) cal/cm2, for clothing or clothing systems for employees working on or near energized lines, parts or equipment. Depending on the voltage, effective arc ratings can range from 4 calories to as much as 60 calories/cm2. Certain meltable fabrics are not allowed.
The NESC also contains requirements that risk factors such as equipment condition and work methods must be considered in implementation of an arc flash program and that a job briefing must be conducted by a first-level supervisor or person in charge.
The CMD6 COOLTOUCH 2™ Deluxe Contractor Coverall is a new product from Bulwark Apparel. The navy flame resistant coverall has an Arc Rating ATPV 10.1 calories/cm² which makes it a Hazard Risk Category 2 garment.
One-piece, topstitched, lay-flat collar › One-piece bi-swing action back › Two-way concealed Nomex® taped brass break-away zipper, concealed snap at top of zipper at neck › Concealed snap closure on sleeve cuff › Two, two-needle topstitched patch chest pockets with flaps and concealed snap closure › Two front swing pockets are topstitched and lined › Two patch hip pockets have single concealed snap closure › One sleeve pocket sewn to left bicep with pencil stall › Rule pocket on right leg › Elastic waist inserts in back.
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Bulwark® is the leading provider of secondary flame-resistant clothing in the world. American Work Apparel is a major supplier of Bulwark garments. Bulwark offer superior flame-resistant protection, comfort, and durability to thousands of workers in electrical utilities and the chemical, oil, gas, mining and petrochemical industries. Bulwark has a 42-year heritage of technical innovation and industry leadership, always remembering that wearer safety is the primary concern. The Bulwark brand makes up the industry’s most comprehensive flame-resistant product line in the broadest range of proven thermal protective fabrics.
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Flame-resistant protective apparel can mean the difference between minor survivable burns and major life threatening injuries.
NFPA 70E – STANDARD FOR ELECTRICAL SAFETY IN THE WORKPLACE
National Fire Protection Association (NFPA) Standard 70E, 2012 Edition addresses electrical safety related work practices for activities such as inspection, operation, repair or demolition of electric conductors, electric equipment, signaling and communications conductors and equipment, and raceways. It also includes safe work practices for employees performing other work activities that can expose them to electrical hazards such as installation of conductors and equipment; or in installations used by the electrical utility, but are not an integral part of a generating plant, substation or control center. The 2012 Edition changed the term “flame resistant (FR)” to “arc rated (AR)” throughout the standard when referring to personal protective equipment (PPE) for electrical workers. Former tables 130.7(C)(10) and (C)(11) on PPE selection when the hazard/risk category method is used were combined into a single table 130.7(C)(16). The new table provides clearer guidance to PPE selection. The HR categories and the arc ratings required for each remain, but the HRC 2* category has been eliminated. A hard hat, hearing protection, safety glasses or goggles, heavy duty work gloves and leather work shoes are required for all HR categories. An arc rated flash suit hood or wrap-around face shield worn with an arc rated hood is required for all HRC 2 – 4 jobs. HRC 0 and HRC 1 tasks require safety glasses or goggles. 70E continues to allow non-melting flammable (non-arc rated) materials to be used as undergarments and permits their use in HRC 0 tasks. However, garments that are not arc-rated cannot be used to increase the arc rating of a garment or a clothing system. Informative Annex H on selection of PPE (the simplified two-category system) was greatly expanded with explanatory material.
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