Arc Flash Training And Arc Flash Clothing Selection: What Arc Flash Calculation Studies Don´t Say

www.e-hazard.com

Recently a large electric utility line worker, we´ll call him Sam, had been badly burned while working near a 69kV piece of equipment. Safety engineering must consider many issues electrical safety training and program development. A lot of these thought processes are not directly addressed in the standards or regulations but they are assumed by them. Thinking through arc flash clothing systems and the electrical safety program can allow compliance and cost savings.

Sam was in a 50 cal/cm² rated winter suit. His garments were provided by his company but he was given latitude on undergarments as long as the outer shell was compliant with the company´s policy.

Sam wore a non-flame resistant sweatshirt this day even though an arc rated option was available in the company catalog. Sam also wore a non flame resistant t-shirt because he though the 50 cal/cm² winter suit was more than protective for the energy levels he would possibly see on their transmission system. Sam´s clothing system complied with OSHA 1910.269, NESC, and NFPA 70E, but it was not the best choice for 69kV. Companies consider OSHA standards, the latest consensus standards like NFPA 70E and the NESC, and the most diligent companies will have engineers perform detailed arc flash studies and label equipment with energy levels. But many companies do not thoroughly think out their full arc flash clothing program. This article introduces a few new concepts you can consider to go beyond standard compliance to more reasonable approach to arc flash hazards.

Most engineers are excited with arc flash today. Shingles have popped up on the internet touting arc flash experts who have EE degrees or PE certifications but little or no real experience beyond software use. Most are NOT experts and often have little more than exceptional knowledge of electrical theory and software calculators. Without knowledge of the standards like IEEE 1584 and the assumptions nad weaknesses in these standards, engineers should be wary of making clothing recommendations based solely on an arc flash study. Clothing companies often claim to be arc flash experts too but few really are and the vast majority are blinded by their product mix. If they don´t sell it, it can´t be good.

Companies should develop their own internal experts to help direct internal policies, provide training, and do internal audits but periodic external expert program audits and periodic system assessment audits will bring much to improve even the best program. Equipment and clothing vendors are a nice free source but an independent qualified electrical program auditor will see things these folks will miss and their value will often be a life saving program tweak which may have little or no cost.

Electric arc flash is a complex phenomenon which is just being better understood in the electrical world. Research on the effect of arc flash on clothing is growing in many ways which are not getting much publicity but the latest research can enhance the effectiveness of your arc flash clothing program. In popular electrical literature you hear of two types of arc (open air and arc-in-a-box) but there are more like four types of arcs. The last two are rarely considered in arc hazard assessments and not really addressed in arc flash studies.

The four types of electric arc are:

1. Open air arc (this is the primary arc used in arc testing)

a. These can be long or short.

2. Arc-in-a-box (this is used in one form for arc testing in the EU)

3. Ejected Arc (when arc plasma hits the worker)

4. Tracking arc (most common at higher voltages, arc plasma conducts on skin or through clothing).

Only the one and two are considered in calculations and standards. The open air arc is well understood. My testing company, ArcWear.com does arc flash testing under lab conditions. We control movement of the arc for the sake of repeatability but in real life from 480V higher the open air arc can quickly turn into an ejected arc or a tracking arc. Tracking arcs are most common at higher voltages or in an electrical contact. Sam was caught in a tracking arc. The standards and calculations didn´t require the best protection for Sam in all cases. Sam would have been best protected if he was wearing arc rated garments over his whole body. Obviously Sam broke several company rules which would have prevented this injury entirely and the company isn´t to blame. But making a program more "forgiving" of worker mistakes by requiring arc rated daily wear makes the most difference.

Arc flash calculations using IEEE 1584 account for some of the effect of an ejected arc but the tracking arc is unaccounted for even in the literature until the last IEEE PCIC meeting in which Dr. David Sweeting an arc flash researcher in Australia published a paper on the subject.

Recently a utility safety engineer explained to me, in a heated meeting, that the NESC doesn´t require them to consider tracking arc at all. This is a misunderstanding of how standards work. Certainly one would like simple, definable OSHA compliance but OSHA standards require protection from "recognized hazards" even if they are not easily definable. Dr. Tom Neal of Neal and Associates and Michael Lang of Ferraz-Shamut introduced "ejected arcs" in several IEEE papers in the past two or three years but this hasn´t gained much momentum (Dr. Neal and I have formed an ASTM taskforce measure this effect on PPE). The new ASTM F2676, of which I am taskforce chair, uses an ejected arc to rate blankets for their resistance to arc plasma in a defined current over time. This might enliven research for better arc flash clothing, protective blankets, shields and even dramatically safer equipment. IEEE 1584 is also doing groundbreaking research on calorimetry and a more complete model of arc in a box.

Because of the newer information we recommend the following steps be included in arc flash hazard assessment.

1. Mandatory clothing for electrical workers should offer choices but it be clear, enforceable and adequate for protection. Pick comfortable clothing; the heaviest weight clothing might not be best. Layering is an excellent choice. Look at lighter weight shirts and arc rated t-shirts. Tracking and ejected arcs are less predictable. Preventing ignition of clothing increases survivability by as much as 90%.

2. Do not allow melting "flame resistant materials" anywhere in the system. Clothing should meet ASTM F1506 (or international equivalent), ASTM F1891 and should be flame resistant for >100 washings.

3. Use arc rated, flame resistant materials especially on the upper torso including undergarments. Underwear ignitions under arc rated outer garments are becoming more common. NFPA 70E-2009 eliminated using cotton underwear in table assessments (cotton may still be used but the specific t-shirt worn should be tested to see when it will ignite. This is NOT the best choice for arc but works well for flash fire exposures.)There are many arc-rated t-shirt options today.

4. Think about moisture management underneath the clothing for worker comfort and reduction of the risk of tracking arc. Arc rated t-shirts may eliminate the use of heavy coveralls in the next few years. Two layers are often MORE protective AND more comfortable to wear.

5. Use clothing systems which provide arc rating in multiple layers rather than just a thick shirt 8 cal/cm² shirt. Though the ease of compliance is easier with a single garment, making all the garments arc rated will almost always provide better protection and the t-shirts could be high visibility (ANSI 107 or CSA Z96) making safety vests less of an issue for roadway exposures. A petrochemical giant in 2009 was considering a arc rated t-shirt to add to their light weight Nomex® coverall because it was more comfortable than replacing the coverall with an 8 cal/cm² coverall.

Hugh Hoagland tests clothing and PPE in the electric arc in his companies ArcWear.com and e-Hazard.com provides arc flash training and arc flash calculation studies.

He may be reached at:

Hugh Hoagland

13113 Eastpoint Park Blvd.

STE E

Louisville, KY 40223

Office: 502-716-7073

Cell: 502-314-7158

www.e-hazard.com

www.arcwear.com