Read NWsp07NFPA70E.pdf text version

NFPA 70E and NETA

Tables, Labels, and HRCs

RonWidup

JimWhite ShermcoIndustries

W

hen using the NFPA 70E, do you understand the tables in Article 130 and how they are intended to be used? Do you apply the parameters of the tables properly? Let's discuss the tables, the labels, and the Hazard/Risk Categories (HRCs). There are two factors in the tables to consider, the hazard and the risk.

The Hazard

When using the tables in 70E the hazard is the estimated incident energy. This is expected to fall into a certain range based on the maximum short-circuit current and the maximum total clearing time of the protective device. In Table 130.7(C)(9)(a), the notes provide the limitations of the table for each type of task and equipment category. If the available short-circuit current or clearing time of the protective device is greater than that specified in the table notes, the table cannot be used. As an example, Note 1 applies to the equipment category, "Panelboards Rated 240 V and Below ­ Notes 1 & 3." Note 1 states, "25 kA short circuit current available, 0.03 second (2 cycle) fault clearing time." If the equipment being worked on exceeds those limits, the table cannot be used to determine Hazard/Risk Categories for those tasks listed. So then how is the arc flash PPE and clothing chosen if the tables cannot be used? The NFPA 70E directs us to perform a detailed arc-flash study, document the incident exposure to the worker in cal/cm2, and choose PPE and clothing based on the incident energy. Article 130.3(B) states (B) Protective Clothing and Personal Protective Equipment for Application with a Flash Hazard Analysis. Where it has been determined that work will be performed within the Flash Protection Boundary by 130.3(A), the flash hazard analysis shall determine, and the employer shall document, the incident energy exposure of the worker (in calories per square centimeter). The incident energy exposure level shall be based on the working distance of the employee's face and chest areas from a prospective arc source for the specific task to be performed. Flame-resistant (FR) clothing and personal protective equipment (PPE) shall be used by the employee based on the incident energy exposure associated with the specific task. Recognizing

that incident energy increases as the distance from the arc flash decreases, additional PPE shall be used for any parts of the body that are closer than the distance at which the incident energy was determined. As an alternative, the PPE requirements of 130.7(C)(9) shall be permitted to be used in lieu of the detailed flash hazard analysis approach described in 130.3(A). FPN: For information on estimating the incident energy, see Annex D.

The Risk

When you look at a specific task in Table 130.7(C)(9)(a), the hazard and the risk are addressed. When assessing the risk associated with a task, some of the issues that need to be considered are: · The age of the equipment and its general design. Does it have venting that would direct hot gases towards personnel? Can it be racked with the door closed, or does it have to be open? Can it be racked, or does it have a lever device? · The condition of the equipment being worked on.

www.netaworld.org

Spring 2007 NETA WORLD

· The maintenance history. Have there been problems and breakdowns with this piece of equipment? Is there a problem with it now? Have there been technical bulletins issued by the manufacturer? · The loading of the equipment. Is it heavily loaded or lightly loaded? Do you have to close a tie breaker before you trip the one you are working on? · The design of the power system. Is it a ring bus, radial bus, or double-ended substation? When it is isolated, what does that really mean? · The skill level of the personnel doing the work. Are they highly experienced, well-qualified? Has it been a while since anyone has done this task? Have they familiarized themselves with the manufacturer's instructions for operating the equipment or are they "figuring it out as they go"?

Also, one must be cognizant of the purposes of the PPErelated tables in Article 130: Table (C)(9)(a) (C)(10) (C)(11) Deals with specific tasks while working on energized equipment Lists the PPE required after the Hazard Risk Category has been determined Lists examples of protective clothing systems and typical characteristics Description

The Tables

The NFPA 70E standard is back in the review cycle and there are several proposals concerning the tables in Article 130 [130.7(C)(9)(a), 130.7(C)(10) and 130.7(C)(11)]. Of the 579 proposals submitted to the NFPA for this review cycle, there are 189 proposals that deal specifically with the tables and each one of them has to be considered and discussed, and action has to be taken by the 70E committee. A Task Group was formed to specifically look at the proposals associated with the tables, and during the recent review sessions the Task Group had some very interesting conversations regarding not just the tables, but their intent and purpose. One discussion revolved around Table 130.7(C)(9)(a) and the Hazard/Risk Categories. It was one of the basic principles of using the tables that both factors, equally important, are an integral part of the table useage. The hazard, as stated earlier, is typically quantified in calories per square centimeter and is the estimated incident energy exposure associated with the task. The risk, which is the element of the equation that becomes very subjective, is the probability of causing or being involved in an arc-flash incident based on the task being performed. The NFPA 70E assumes the electrical devices have been properly engineered, designed, installed and maintained -- and if not, 70E is not going to help. These factors are also considerations in a risk assessment.

An important point to note is that you cannot apply the HR categories of Table (C)(9)(a) unless you are performing the same task as listed within the Table and you meet all of the requirements of the notes. If your particular situation is not the same as listed in the Table or does not meet the requirements of the notes then you cannot use the Table, and you must perform a detailed flash-hazard analysis. If you have not performed a flash-hazard analysis, be aware that you cannot use the Hazard/Risk Categories listed in Table (C)(9)(a) and work backwards into Table (C)(11) by selecting a task that has a particular Hazard Risk Category indicated in (C)(9)(a). For example, you have a task to rack out a 480-volt circuit breaker in 600 V class switchgear with the door open (shown in (C)(9)(a) as a Hazard/Risk Category 3) and you don't know or haven't met the requirements of the table notes. You cannot assume the task of racking out all 480-volt circuit breakers to be a HRC 3 task and apply the clothing system with a minimum arc rating of 25 calories per square centimeter as indicated in Table (C)(11). You must perform a complete flash-hazard analysis and quantify the hazard to verify the required level of PPE.

The Labels

When using the arc-flash warning labels, be aware that they typically state the level of hazard in calories per square centimeter and a defined working distance, but they do not take into account the risk. That's one reason why the tables and the labels should not be mixed together. The tables are task-based; the labels are hazard-based. See Figure 1 for an example of an arc-flash label. When using the labels, it may be possible to lower the amount of PPE based on risk, if that is what the risk assessment indicates. Performing a thermographic infrared scan is one example where the hazard may be high, but the risk may potentially be low. Typically it is noninvasive and can often be performed three or more feet away from the equipment being scanned, and except for during the removal of panels the plane of the switchgear is not typically broken. For example, a piece of equipment has a label that indicates an incident energy exposure of 8.2 calories at an 18 inch working distance. This would be classified as an HRC 3 situation (8.1 ­ 25 calories) so because of the working distances involved in the IR task, www.netaworld.org

NETA WORLD Spring 2007

!

252 inch 38.2 cal/cm 2 Class 4 480 VAC 00 42 Inch 12 Inch 1 Inch

WARNING

Flash Hazard Boundary Flash Hazard at 24 Inches Cotton Underwear + FR Shirt & Pant + Multi Layer Flash Suit Shock Hazard when cover is removed Glove Class Limited Approach Restricted Approach Prohibited Approach

Arc Flash and Shock Hazard Appropriate PPE Required

based on the overall equipment condition, personnel, and specific tasks to be performed under the conditions that you have at that moment in time. While there are other factors to be considered as well, performing a risk assessment is critical to worker safety, regardless of whether the tables are used or an arc-flash analysis is performed. Be safe out there and keep your workers informed and safe!

Bus: 3USS 480 V BUS Prot: 3USS MAIN Figure 1 -- Arc-Flash Warning Label

reducing the level of PPE for the camera operator could be an option, based on the risk assessment. The personnel removing panels, however, would have a higher level of risk as they would be closer to the exposed part and using tools that could possibly drop into the equipment. Many programs and companies performing arc-flash hazard analysis put the Hazard/Risk category on their labels in an attempt to guide workers to the correct PPE and clothing; however, one should be careful not to mix the two concepts, tables and labels. Whether the tables or arc-flash warning labels are used, always perform a risk assessment

Ron A. Widup and James R. White are NETA's representatives to NFPA Technical Committee 70E (Electrical Safety Requirements for Employee Workplaces). James R. White is nationally recognized for technical skills and safety training in the electrical power systems industry. He is currently the Training Director for Shermco Industries, a NETA Full Member company. Jim has spent the last twenty years directly involved in technical skills and safety training for electrical power system technicians.

www.netaworld.org

Spring 2007 NETA WORLD

Information

3 pages

Find more like this

Report File (DMCA)

Our content is added by our users. We aim to remove reported files within 1 working day. Please use this link to notify us:

Report this file as copyright or inappropriate

566247


You might also be interested in

BETA
PM710 Installation.fm
05-1741.cdr