Electrical & Product Safety Observations For 2012

It is hard to believe, but 2012 is almost over.  Last November, I wrote on the Electrical and Product Safety blog about the top safety mistakes that I observed in 2011.  Instead of looking at mistakes in 2012, I am going to look at both “good” and “not so good” observations related to electrical and product safety.

In the not so good category, my observations are follows:

·        Not designing or purchasing equipment that minimizes electrical hazards during operation or maintenance (repeat from last year)

·        Not using basic statistical techniques to determine equipment safety and reliability (repeat from last year)

·        Not using basic statistical techniques to identify vendor performance – more of quality problem than a safety problem, but still an important observation

·        Not fully understanding the design parameters associated with equipment

·        Organizations struggling with defining and implementing regular maintenance of electrical infrastructure equipment

·        Organizations struggling with management of change processes

 In the good category, my observations are as follows:

·        More people are aware of hazards associated with working on or near exposed live (energized) equipment

·        More people are asking for their equipment to be analyzed by safety experts

·        More people are participating in various type of webinars or classroom training associated with all aspects of safety

·        More organizations are conducting shock and arc flash hazard analysis of their electrical equipment

·        ElectricalProductSafety.blogspot.com has had a large increase in readers

In 2013 I plan on branching out from the requirements of NFPA 70E into other items associated with electrical and product safety.  I plan on looking at the design of equipment and applications.  Some of the topics will examine requirements from standards while others will be “best practices”. 

As you start thinking about your electrical and product safety goals for 2013, I would like to leave with one thought from a manufacturing colleague of mine from many years ago.  That thought is “What gets measured, gets done”. 

When you make you safety goals for 2013 (or anytime), make sure that these goals can be measured and do not be afraid to display your metrics.

Have a Safe and Happy New Year!

 

Shock & Arc Flash Analysis of DC Electrical Systems

Most concepts of electrical safety revolve around AC electrical systems.  While AC electrical systems are the most prevalent in the workplace, DC electrical systems are being used in more applications and equipment, e.g. photovoltaic (PV) systems, within UPS equipment, control cabinets, industrial machines and telecommunication systems.

In the most recent edition (2012) of the Standard for Electrical Safety in the Workplace, NFPA 70E, information to protect qualified employees from the shock and arc flash hazards associated with working on exposed live (energized) circuits in DC systems is starting to be addressed.  As noted in Table 130.4(C)(b), the limited, restricted, and prohibited approach boundaries for workers working near or on exposed live (energized) electrical conductors in direct current (DC) electrical systems are provided [1]. 

For DC electrical systems operating at less than 100Vdc, the limited, restricted, and approach boundaries are not specified.  For DC electrical systems operating at 100 Vdc to 300 Vdc, the limited approach boundary is 42 inches, while the restricted and prohibited approach boundary is to simply avoid contact.  For DC electrical systems operating at 301 Vdc to 1,000 Vdc, the limited approach boundary is 42 inches, the restricted approach boundary is 12 inches, and the prohibited approach boundary is 1 inch.

While shock hazard boundaries are now identified, information associated with arc flash boundaries, incident energy associated with DC electrical systems is not specified differently than AC electrical systems.  Additionally, the common electrical simulation tools do not have the capabilities to calculate the arc flash boundaries and incident energy for DC electrical systems.

The literature on arc flash hazards associated with DC electrical systems is limited [2, 3, 4].  While limited, this research data combined with an additional understanding of how DC electrical systems are rectified from AC electrical systems will add to the understanding of the shock and arc flash hazards for a DC electrical system [5].  When combining literature, interpolation of overcurrent protective devices, an understanding of the DC electrical system parameters, and equipment, an engineer can create a mathematical model that will adequately represent the arc flash boundaries and incident energy for a DC electrical system.

Once the shock and arc flash hazard analysis for electrical equipment connected to the DC electrical system has been evaluated, the equipment is required to be labeled in accordance with NFPA 70E and ANSI Z535.4.

For more information on electrical and product safety, please comment on this blog or send me an e-mail. 

References:

1.     National Fire Protection Association (NFPA), Standard for Electrical Safety in the Workplace, NFPA 70E – 2012, Quincy, MA USA.

2.     Ammerman, R.F., Gammon, T, Sen, P.K., and Nelson, J.P. (2010), DC-Arc Models and Incident-Energy Calculations.  IEEE Transactions on Industry Applications, Volume 46, Number 5.

3.     Doan, D.R. (2010).  Arc Flash Calculations for Exposures to DC Systems.  IEEE Transactions on Industry Applications, Volume 46, Number 6.

4.     Fontaine, M.D. and Walsh, P (2012).  DC Arc Flash Calculations – Arc-in-open-air & Arc-in-a-box – Using a Simplified Approach (Multiplication Factor Method).  IEEE Paper No. ESW2012-25.

5.     RailCorp (2010).  Rectified Transformer & Rectifier Characteristics.  Document EP 03 00 00 01 TI, Version 3.0, Issued May 2010.

 

Electrical Safety - When Can You Work on Energized Circuits?

Technicians and maintenance personnel often need to work on exposed live (energized) circuits to troubleshoot or perform maintenance on electrical systems or equipment. 

The Occupational Safety and Health Administration (OSHA) and the National Fire Protection Associated (NFPA) provide guidance on working on exposed live (energized) circuits.  OSHA 29 CFR 1910 requires that work on electrical systems or equipment shall be de-energized unless de-energizing the circuits could create a greater hazard or if it is infeasible to de-energize the circuits.  The requirements identified in NFPA 70E, Standard for Electrical Safety in the Workplace, Articles 130.1(A)(1) and 130.1(A)(2) are similar to the OSHA requirements.

There are at least three classifications of electrical circuits that if they were de-energized could create a greater hazard to other people: emergency circuits, legally required standby circuits, critical operation power system (COPS) circuits.  Emergency, legally required standby, and COPS circuits are defined by NFPA 70, National Electrical Code, in Articles 700, 701, and 708 respectively.  Emergency circuits are identified as those systems that provide safe exit and communication within a building or other areas associated with life safety (e.g. patient rooms, operating rooms, or other areas within a hospital) [1].  Legally required standby circuits are identified as those systems that if stopped could result in general public safety hazards (e.g. sewage treatment facilities, pollution abatement systems, chemical processes, etc.) [1].  COPS circuits are identified as those systems that vital to national security, the economy, and public safety [1].  De-energizing emergency, legally required standby, or COPS circuits could endanger other personnel.  Therefore, technicians and maintenance personnel are allowed to perform work on these systems.

Optional standby systems, and unclassified systems are other types of electrical systems.  However, these systems in general do not pose a greater hazard to other personnel if they are de-energized like emergency, legally required standby or COPS systems.

When working on exposed live (energized) circuits an electrical hot work permit, risk assessment, and job safety meeting are required prior to conducting the work on exposed live (energized) circuits [2].  Items to be considered in the risk assessment are work practices that could result an inadvertent de-energizing of the electrical system due to human error or equipment malfunctions.

There are a number of work practices where it is infeasible for qualified employees to de-energize the electrical system or equipment regardless of their classification.  This includes troubleshooting, measuring, and adjustment of equipment.  Troubleshooting and measuring of electrical systems or equipment often involves measuring voltage, current, power, phase or other electrical quantities that cannot be observed without electrical energy present.  Adjustment of servos, indicators and similar devices also require electrical energy.

When qualified employees are conducting troubleshooting, measurement, or adjustment of electrical systems or equipment in the presence of exposed live (energized) circuits, a risk assessment and a job safety meeting are required prior to conducting the tasks.  As aforementioned, a risk assessment that evaluates the inadvertent de-energizing of the electrical system due to human or equipment malfunctions should be considered.

1.  National Fire Protection Association (NFPA). National Electric Code, 2011.
2.  National Fire Protection Association (NFPA). Standard for Electrical Safety in the Workplace, 2012.

When Do I Need An Electrical Hot Work Permit?

The other day I was asked, when do you need to have an energized or electrical hot work permit?  Also, what needs to be on the energized or electrical hot work permit? 

The Standard for Electrical Safety in the Workplace provides the requirements of when an energized or electrical hot work permit is required.  An electrical hot work permit is required whenever qualified persons are working within the limited approach or the arc flash boundary, whichever is greater (Figure 1) [1].  In a 480 V system, the default limited approach boundary is 42 inches and the default arc flash boundary is 48 inches.  The arc flash boundary can be reduced by conducting an arc flash hazard analysis, but the limited approach boundary is based on system voltage (see Table 130.4(C)(a) and Table 130.4(C)(b) in NFPA 70E).

There are some cases when an electrical hot work permit is not required.  An electrical hot work permit is not required when qualified persons are conducting tasks such as testing, troubleshooting and voltage measuring [1].  Similar tasks that are not explicitly defined but inferred are conducting power quality measurements, current measurements, calibrating of systems, adjustment of components and other similar tasks where the equipment must be energized to verify proper operation.  Other tasks where an electrical hot work is not required include energizing or de-energizing equipment, or conducting visual inspections, infrared inspections and the like.  Also, any type of work on equipment where the voltage is less than 50 V does not require an electrical hot work permit, unless it is in the proximity of the limited approach or arc flash boundary of exposed live (energized) circuits or parts.

An electrical hot work permit is required for activities not mentioned above.  This includes installing new components, e.g. circuit breakers, conductors, printed wiring boards, etc. Also, an energized or electrical hot work permit is required whenever this type of work is conducted on equipment where the voltage is 50 V or greater. 

Electrical work permits can vary.  The minimum requirements are [1]:

• Description of the circuit and equipment to be worked on and location
• Justification for why the work must be performed in an energized condition
• Description of safe work practices
• Results of the shock hazard analysis including the limited approach, restricted approach, and prohibited approach boundaries
• Results of the arc flash hazard analysis including the incident energy and arc flash boundary
• Appropriate shock and arc flash hazard PPE
• Method to ensure on qualified persons are allowed in the limited approach or arc flash boundaries
• Evidence of the completion of job briefing
• Approval by management, safety officer, owner, or other company official

While utilizing PPE, energized safe work practices, or requiring energized or electrical hot work permits can help establish safe working conditions when working around or on exposed live (energized) circuits or parts, the safest method of working on electrical circuits is to de-energize these circuits or parts.

For this and other questions on electrical or product safety, please comment to this blog or send me an e-mail.

References:

1. National Fire Protection Association (NFPA).  Standard for Electrical Safety in the Workplace, NFPA 70E, 2012.  Quincy, MA USA

Electrical Safety Training - Shock & Arc Flash Hazards

The primary standard in the US that determines the requirements for electrical safety training is the National Fire Protection Association’s (NFPAs) Standard for Electrical Safety in the Workplace, NFPA 70E.

Employees who work around electrical equipment, but are not those defined as qualified employees, are required to be trained such that they have sufficient information needed to provide for their safety.

Employees who are work on energized live (exposed) circuits operating at 50 V or more are required to be qualified.  Qualified Employees are defined as employees that are knowledgeable of the construction, installation, and operation of the equipment, and who has been trained to recognize and avoid the hazard associated with working on the equipment.  Qualified Employees are required to have electrical safety training.  Electrical safety training can be conducted in a classroom, through on-the-job mentoring, or a combination of the two. 

Topics that Qualified Employees should be trained to include:

• OSHA requirements for electrical safety
• NFPA 70E requirements for electrical safety
• Electrical work permits
• Electrical hazards
• Risk assessments
• Shock hazard boundaries
• Arc Flash boundaries
• Personal protective equipment
• Types
• Proper wear and fit
• Limitations
• Maintenance and care
• Equipment labeling
• Methodologies to reduce electrical hazards
• Proper use and limitation of electrical test equipment

Qualified electrical safety training should include methods that show the employee understands the electrical safety material.  This can be through tests, practical examinations, or demonstrations.

Once a Qualified Employee has been trained, the employer shall determine competency to electrical safety related work practices on an annual basis.  Annual competency can be determined through regular supervision, or inspections. 

A Qualified Employee shall receive additional electrical safety training when:

• Supervision indicates the employee is not complying with safety related work practices
• Annual inspections indicate that the employee has insufficient knowledge of safety related work practices
• New technology or equipment necessitate changes in safety related work practices
• If the employee is required to employ non-standard safety related work practices

For this and other questions on electrical and product safety, please contact me via comments on this blog or through e-mail.

Equipment Labeling Requirements – Shock & Arc Flash Hazards

Prior to the 2012 version of the National Fire Protection Association’s (NFPA) Standard for Electrical Safety in the Workplace, NFPA 70E, there were minimal equipment labeling requirements to detail the hazards associated with shock and arc flash on electrical equipment.  The only requirements for the labeling of equipment are where found in NFPA’s National Electric Code, NFPA 70, Article 110.16.

110.16 Arc-Flash Hazard Warning.  Electrical equipment, such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers, that are in other than swelling units, and are likely to require examination, adjustment, servicing, or maintenance while energized shall be field marked to warn qualified persons of potential electric arc flash hazards.  The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.

Informational Note No 1. NFPA 70E-2009, Standard for Electrical Safety in the Workplace, provides assistance in determining severity of potential exposure, planning safe work practices, and selecting personal protectiveequipment.

Informational Note No. 2. ANSI Z535.4-1998, Product Safety Signs and Labels, provides guidelines for the design of safety signs and labels for application to products.

From the above requirements, a simple warning label would be sufficient.

To comply with the 2012 version of NFPA 70E, shock and arc flash labels are required to have the following information:

1.      One of the following

                  a.       Available incident energy and
                         corresponding working distance
                  b.      Minimum arc rating of clothing
                  c.       Required level of personal protective equipment (PPE)
                  d.      Highest Hazard/Risk Category (HRC) for the equipment
      2.      Nominal system voltage
      3.      Arc flash boundary

To have a shock and arc flash hazard label that meets the requirements of NFPA 70E and the intent of NFPA 70, requires that the labeling requirements for ANSI Z535.4 be included as well.

The requirements for labeling as detailed in ANSI Z535.4 can be summarized as follows:

1.      Identify the Hazard – What can go wrong (picture or graphic)

      2.      Consequence – What will happen (text)
      3.      Seriousness – How bad will one get hurt (DANGER, WARNING, CAUTION)
      4.      Avoidance – What you can do to prevent the hazard (text)

The label below shows one label that meets all of the requirements of NFPA 70E and ANSI Z535.4; there are other formats that will meet those requirements.
This example shows a label that has all of the essential information to fully comply with the requirements to “warn qualified workers of potential arc flash hazards”. 

Because NFPA 70E-2012 is a new standard, when will the new labels be required to be installed and on what equipment?  As most are aware, NFPA 70E is not a standard that is enforceable by code.  However, complying to the requirements of NFPA 70E is one method of complying with requirements for employee safety in the US.  The Occupational Safety and Health Administration (OSHA) recognizes NFPA 70E and numerous other consensus standards to ensure that employers are providing a workplace that is free from known hazards. 

Because it is not code, there is no “grandfather” clause.  Therefore, adoption of the new requirements should proceed as quickly as possible.  This requires that all employers who want to ensure that they are complying with OSHA requirements should start a program to transition all shock and arch flash hazard labels to meet the requirements detailed in NFPA 70E, NFPA 70 and ANSI Z535.4.

For this and other questions on electrical and product safety, please contact me via comments on the blog or through an e-mail.

NFPA 70E - Electrical Safety Program

NFPA 70E, Standard for Electrical Safety in the Workplace, is the most commonly used consensus document for determining safe work practices when working on or near exposed live (energized) circuits or parts.  In November 2011, the National Fire Protection Association (NFPA) released the 2012 edition of the NFPA 70E.  As with any revised standard, there are a number of changes that have been incorporated.  Over the course of this year, I will detail a number of the new or changed requirements.

The focus of this segment is the requirements of the Electrical Safety Program.  The previous edition of NFPA 70E required an electrical safety program, but there are additional requirements.  The fundamental concepts that should be considered in the implementation of an Electrical Safety Program are:

1.     Electrical Safety Program Principles

a.     Scope

b.    Definitions

c.     Responsibilities

2.     Electrical Safety Program Procedures

a.     Applies to work on exposed live (energized) circuits 50 V or greater

b.    Identify procedures for working within the limited approach boundary

c.     Identify procedures for working within the arc flash boundary

3.     Electrical Safety Program Controls

a.     Shall include appropriate controls

b.    Shall include training requirements

c.     Include all appropriate precautions

4.     Hazard Identification and Risk Assessment Procedure

a.     Required whenever personnel are entering the limited approach boundary or arc flash boundary

b.    Shall include potential risks and mitigation strategies

c.     Must be conducted prior within the limited approach boundary or arc flash boundary

d.    Shall be documented and filed

5.     Job Briefing

a.     Required for all personnel who will be working within the limited approach boundary or arc flash boundary

b.    Shall be documented and filed

6.     Electrical Safety Program Audit

a.     The Electrical Safety Program shall be audited at least every 3 years

b.    The audit process shall be documented

c.     The audit process should be conducted by personnel who understand electrical safety and are trained auditors

While the standard provides specific requirements of the Electrical Safety Program, it is also important that the program be designed in a manner that would allow for easy implementation.

If you would like more information on the creation, implementation, or auditing of the Electrical Safety Program, please send me an e-mail or comment on this blog.

Are Standards Too Expensive?

In the classes I teach and in many discussions with customers from various industries, I invariably have a discussion about the procurement of standards.  Some have no problems buying the standards needed to evaluate their materials, equipment, machines or processes.  However, a percentage of customers state that standards are “too expensive” to procure.

Standards are developed by a number of organizations that describe the design, installation, performance and safety of products, materials, equipment, and machines.  Common standards organizations are as follows:

• American National Standards Institute (ANSI),
• ASTM International, formerly the American Society for Testing and Materials (ASTM),
• National Fire Protection Association (NFPA),
• International Electrotechnical Commission (IEC),
• Institute of Electrical and Electronic Engineers (IEEE),
• National Electrical Manufacturers Association (NEMA), or
• Robotics Industry Association (RIA)
• SAE International, formerly the Society for Automotive Engineers (SAE)
• Underwriters Laboratories (UL),

Most standards organizations have various rules about who is involved with the development and voting of standards.  Many standards organizations require a combination of people from the equipment or material manufacturers (defined as "manufacturers"), people that use the equipment or materials (defined as “users”), and people from academia, non-related organizations (defined as “general interest”) to be part of the standards development and/or voting groups.

Standards are one method that the standards organization uses to fund various activities.  The price of most standards vary from "free" to $2,000 (US), while most are in the $100 to $500 range.  While some standards may seem expensive, when these prices are put into perspective of development costs and independent testing costs.  Development costs range from tens to hundreds of thousands dollars or even millions of dollars depending on the complexity of the material, equipment, machine or process.  Independent testing can costs range from $10,000 to $25,000 or more, and that does not include the resources of time and equipment needed by the organization.

From my experience, the price of procuring standards is not an issue of price, but a mask of some other underlying problem(s) within an organization.  These underlying issues vary from organization to organization.    When one evaluates the price of standards, the evaulation should include the costs associated product development, or the costs of product recalls or injuries from their products, not just the price of the standard.

The procurement of the appropriate standards are important in validating the safety and/or performance of materials, equipment, machines or processes and are far less expensive than costs related to product redesign, product recalls, or an injury from an unsafe product.

Statistical Sampling

Many product safety standards require that 3-samples pass a specific test to show that the product sufficiently meets a requirement. In most cases three samples is not a sufficient sample size to determine statistical validity. The sample size of a known population size can be calculated based on desired precision and confidence level and is determined by [1]:

The variables in EQ1 are defined as: n = samples size, N = population size, P = estimated population within compliance, Q = 1-P, B = allowable error (precision), and s = desired level of confidence

Specifically, in UL 1449 (Standard for Safety, Surge Protective Devices), assessing how a surge protective device (SPD) fails from an abnormal overvoltage limited current (ABOV-LC) requires that three samples be tested [2].  Three samples of SPDs are subjected to the test.  If the SPDs meet the minimum pass criteria for each mode (line-to-neutral, line-to-ground, neutral-to-ground), then the SPD has successful met the requirements of the test. While the SPD may meet the minimum requirements, it easy to state that this is not a statistically valid.

To determine the number of samples required to have a statistical valid representation for the product, let’s use the following data in EQ1.

·         Anticipated number of SPDs to be manufactured (N) is 10,000

      ·         Percentage of each unit for the mode of protection is 0.429
                  o    3-phase SPD
                  o    Line-to-Neutral protection (Phase A-N, Phase B-N, and Phase C-N)
                  o    Line-to-Ground protection (Phase A-G, Phase B-G, and Phase C-G)
                  o    Neutral-to-Ground protection (N-G)
      ·         Allowable error (B) or failure rate of 10 percent
      ·         Desired confidence level (z) of 95 percent.

Based on the data, the number of samples that should be evaluated for a statistically valid experiment is 93 test samples for the line-to-neutral mode, assuming that all line-to-neutral modes are identical.  This is considerable more than the 3 samples required by the UL test standards.

If the company can accept an allowable error of 20 percent, the number of samples that should be evaluated is reduced to 23 samples.

All too often I see where a company has subjected their SPDs or other equipment to the test programs designed only to pass relevant safety standards.  While this proves compliance with the standards, this does not prove that the tests results are statistically valid nor do they accurately reflect the performance attributes of the equipment.  Establishment of a baseline of the equipment’s performance can only be accomplished through statistical sampling.

Reference:

1. Underwriters Laboratories (2007), Standard for Safety, Surge Protective Devices, UL 1449 3^rd edition, Northbrook, IL USA
2. Anderson, D.R., Sweeney, D.J, Davis, D., Utts, J.M, Williams, T.A., and Simon, M (2001).  Statistic and Research Methods for Managerial Decisions.  South-Western, Thomas Learning.