Engineering Methods of Hazard Reduction & Mitigation

Many safety leaders have stated that they do not allow qualified employees to work on or near exposed live (energized) circuits.  They have created a policy that all energized circuit shall be de-energized and locked and tagged (LOTO) per specific control of hazardous energy policies.  This is a great policy, but it is not always feasible.

There are some systems that cannot be easily de-energized.  OSHA's requirement for working on energized equipment is “Live parts to which an employee may be exposed shall be deenergized before the employee works on or near them, unless the employer can demonstrate that deenergizing introduces additional or increased hazards or is infeasible due to equipment design or operational limitations” [OSHA 29 CFR 1910.333(a)(1)]. 

Electrical systems that are identified as emergency systems (NFPA 70, Chapter 700), legally required systems (NFPA 70, Chapter 701), and critical operating power systems (NFPA 70, Chapter 708) cannot be de-energized unless permission is obtained from the appropriate governmental authority have jurisdiction (AHJ).  Emergency power systems are critical for life safety and include many healthcare facilities.  Emergency power systems are also located in every public building and include emergency lighting for egress and fire suppression, alarm, and communication circuits.  Legally required power systems include those systems that if de-energized, can create a greater hazard to the community.  Legally required power systems include those systems that control pollution abatement systems, chemical containment systems, and the like.  Critical operating power systems include those systems that critical to functionality of the US.  This includes water, transportation, energy, transportation, and specific monetary functions.

Another type of power system is the optional power systems (NFPA 70, Chapter 702).  Optional (nonessential) power systems are those systems and loads that are related to business continuity.  These power systems can be de-energized without creating safety hazards, although they may impact the business.  

In addition to systems that cannot be de-energized easily because of legal requirements, specific activities such as troubleshooting, testing and measuring of voltage, current, power or related parameters must be conducted when electrical equipment is energized on all types of power systems [NFPA 70E-2015, Chapter 130].  There are other activities that may also require qualified personnel to interact with exposed live (energized) circuits.  This includes the adjustment and programming of equipment.  These activities can be conducted on all types of electrical systems and in locations such as manufacturing environments, R&D laboratories, production testing environments, and many more.

Last month’s blog focused on the Administrative Methods of hazard reduction and mitigation of electrical hazards.  While administrative methods can be effective, they also present an opportunity for injuries to occur.  Hazard reduction and mitigation techniques are more reliable and effective when Engineering Methods are implemented.

The Engineering Methods of hazard reduction and mitigation of electrical hazards include:

• ·         Elimination
• ·         Substitution
• ·         Guarding
• ·         Safety Control Systems

Guarding of electrical hazards are what is accomplished by equipment enclosures.  Enclosures protect all people who are in close proximity to the equipment from interacting with the equipment.  However, when qualified employees need to conduct troubleshooting or testing, they need to have access to the exposed live (energized) circuits.

Safety control systems are typically devoted to keep employees out of a hazardous area and can be very loosely similar to guarding principles.  Common equipment associated with safety control systems include using light-curtains, pressure mats, interlocks, or other components tied into a safety rated programmable logic controller (PLC).

The substitution principle can be used by changing the operating voltage that the qualified employee is required to interact with.  This includes changing control voltages from 120V or 240V to 24V.  The 24V control circuit can be located in a separate cabinet that is isolated from any circuit that is 50V or greater.  Qualified employees working on system voltages of 24V are generally not exposed to shock or arc flash hazards.

To eliminate electrical hazards, designers and engineers can remove the need for people to interact with exposed live (energized) circuits.  This includes designing equipment such that user interface equipment is located on the front panel of the equipment.  Examples include using HMI’s, remote panels for SCRs or other industrial control components, remote communication interface ports, etc.  Eliminating qualified personnel from interacting with exposed live (energized) circuits can be achieved on new equipment that is in the design phase, but is not very practical for equipment that is already installed.

As the term Engineering Methods suggests, engineering activities are required to assess the risks of the activities, and to reduce or mitigate the hazards.  For qualified employees working on exposed live (energized) circuits, the implementation of engineering methods to reduce or mitigate arc flash hazards will result in a safer workplace.

Administrative Methods to Mitigating Electrical Hazards

The rules surrounding electrical safety continue to change.  There are three main components that are affecting change: scientific data, safety professionals, technology.  Researchers continue to develop and communicate new understanding of shock, arc flash, and other electrical hazards.  Safety professionals are working hard to set a safe working culture within the workplace.  Technology is being created to mitigate electrical hazards. 

There are multiple methods to reduce hazards.  Risk reduction techniques are commonly divided into engineering and administrative controls.  Reducing hazards through engineering methods (elimination, substitution, guarding, and safety controls) is preferred over administrative methods (operating procedures, training, and personal protective equipment).

However, most of the efforts to reduce employees to electrical hazards have been focused on administrative methods.  The use of administrative methods (operating procedures, training, PPE, signage) is not the same as eliminating the hazard, guarding the hazard, or using safety controls to eliminate access to the hazard.

Companies are implementing safe work practices, electrical safety training programs and procuring shock and arc flash personal protective equipment (PPE).  The Standard for Electrical Safety in the Workplace, NFPA 70E, provides guidance for standard operating procedure, training, and personal protective equipment (PPE) for qualified people working on or near exposed live (energized) circuits. 

Safe work practices associated with electrical safety include the control of hazardous energy (Lockout Tagout) procedures, procedures for working on exposed live (energized) circuits, and electrical hot work permits.  OSHA requires that each company is responsible for developing, implementing, auditing the safe work practices to ensure that their employees have safe work conditions.

Companies are ensuring that employees who are working on or near exposed live (energized) circuits complete electrical safety training programs.  The consensus is that comprehensive electrical safety training is to be conducted at least every 3 years, and annual competency of refresher training be conducted every year between the comprehensive electrical safety training.  Electrical safety training is required for everyone who works on or near exposed live (energized) circuits where the voltage is 50 V or greater, or if the energy available can expose employees to shock or arcing hazards.  The elements of an electrical safety training include definition of hazards, safe work practices, use of PPE, use of tools, and understanding arc flash labels.  Testing is required to ensure that employees understand the concepts taught.  Testing should include a written test and practical examination.

PPE is used to protect employees from shock and arcing hazards.  Shock hazard PPE include voltage rated gloves, blankets, and mats.  Arcing hazard PPE include hard hat, leather gloves, leather shoes, arc rated clothing, arc rated face shield or arc rated hood, and safety glasses.  The rating of the PPE is determined through the calculation of the voltage (shock) and incident energy (arcing) energies.  Shock hazard PPE is identified by Class.  Arcing hazard PPE is identified by Category or Incident Energy Rating.  Employees working on or near exposed live (energized) circuits are required to wear BOTH shock and arcing hazard PPE.

Companies have used administrative methods as these are well known and can be easily identified in the company budget.  When implementing any component of the administrative methods to reduce shock and arcing hazards, it is important to have experienced and knowledgeable professionals involved.  The writers of the safe work practices can only produce effective procedures is done by competent technical writers with knowledge of the process and how to write effectively.  Training employees can only be effective when the trainer is a trained professional experienced in the craft of teaching and electrical safety.  The PPE used must be certified, regularly tested, and verified it is serviceable prior to each use.

The use of operating procedures, training, and PPE can reduce accidents associated with electrical hazards.  However, administrative methods are not as effective at reducing accidents as engineering mitigation techniques.

NFPA Electrical Safety Standards Update

It is amazing how quickly time passes.  I had intended to put together a series of electrical safety topics that focused on the basics of electrical safety and then some mitigation techniques, but time got the best of me7.  So, before we get too far, I want to step back and briefly discuss the trilogy of electrical safety standards with updated information.

As you know from reading past blogs, there are three standards from the standards from the National Fire Protection Association (NFPA) that contribute to an organization’s electrical safety program: National Electric Code (NFPA 70), Recommended Practice for Electrical Equipment Maintenance (NFPA 70B), and The Standard for Electrical Safety in the Workplace (NFPA 70E).  Equipment that is not properly installed or properly maintained can create safety hazards.

The foundational standard of electrical safety is equipment design and installation.  The 2017 version of the National Electric Code (NEC) provides the minimum design and installation requirements for electrical equipment.  The 2017 version is available as a PDF download; hard copies will be available in October.  The NEC describes how to apply equipment, conductors, grounding, overcurrent protective devices, and other devices.  When equipment and components are designed and installed in accordance with the NEC, there are minimal potential for shock and arc flash hazards. 

Article 110.16 of the NEC requires that all equipment, other than those installed in swellings, that are likely to require examination, adjustment, servicing, or maintenance while energized to be marked to warn qualified persons of the potential arc flash hazards.  This includes switchboards, panelboards, motor control centers (MCCs) and industrial control panels.  This can also include transformers, UPSs, transfer switch equipment, and junction boxes where power distribution blocks are used to splice conductors.  Arc flash labels should meet American National Standards Institute (ANSI) standard Product Safety Signs and Labels, ANSI Z535.4-2011.

The second standard of electrical safety is maintenance.  The latest edition of the Recommended Practice for Electrical Equipment Maintenance (NFPA 70B), which was published in 2016, and provides details on the development of an electrical preventative maintenance program (EPM) and basic maintenance requirements for common electrical equipment.  NFPA 70B can be used when specific maintenance procedures from the equipment manufacturer are not available.

The third and final standard of electrical safety is The Standard for Electrical Safety in the Workplace(NFPA70E), which was last published in 2015.  NFPA 70E provides the basic requirements for working on or near energized equipment when the guards (enclosure doors or panels) are removed and electrical energy is present.  Shock and arcing hazards are present whenever qualified employees are working on or near equipment when enclosure doors or panels are removed, and electrical energy is present.  If the equipment is properly installed and properly maintained, then any work or troubleshooting that could be required while the equipment is energized should follow the guidelines of NFPA 70E. 

Standards are developed to provide people and organizations with basic knowledge and guidance.  Ensuring that equipment is properly designed and installed (NFPA 70), properly maintained (NFPA 70B) and people working on or near exposed live (energized) circuits are trained, have procedures, and protective equipment (NFPA 70E) will limit personnel to shock and arc flash hazards.

The Proper Installation of Equipment is the Foundation to Electrical Safety

As I noted in last month’s blog, there are three components to ensuring personnel are safe from workplace hazards associated with equipment:

• Proper Installation of Equipment (normal operation)
• Proper Maintenance of Equipment (maintenance)
• Proper Safety Procedures when working on or near Energized Circuits (abnormal operation)

The National Electrical Code (NFPA 70) describes the minimum requirements for the installation of equipment.  Components (e.g. circuit breakers, fuses, conductors, etc.), equipment (e.g. switchboards, industrial machines, control panels, surge protective devices, etc.), and systems (e.g. emergency power, etc.). All components, equipment, and systems have general and specific minimum requirements to ensure safe installation and operation.  While there are a number of general requirements, the three general requirements that I think are the most important to ensure that the equipment is safe for operation are Article 110.3, Article 110.10, and Article 110.16.

The first important requirements (NFPA 70, Article 110.3) is that equipment be suitable for the environment, of sufficient mechanical strength, and be installed and used in accordance with any manufacturer’s instructions, listing, or labeling requirements.  This broad requirement is intended to make sure that the equipment is used in accordance with its intended application.  For example, if an industrial machine is intended to be intended to be connected to a power source with a rated voltage of 208Y/120, 3-phase Delta, 4W+G, then connecting to a power source of another voltage can cause the machine to be inoperable or create a hazardous condition.

The second important requirement (NFPA 70, Article 110.10) is that the short circuit current rating (SCCR) of the equipment be equal to or greater than the short circuit (fault) current at the point of application.  If the analysis of the power system finds that the short circuit at a specific point in the power system is 33,500 A, then any equipment installed at that point must have a short circuit current must have a SCCR that exceeds 33,500 A.  Common values of SCCR range from 5,000 A to 200,000A.  The next closest SCCR value to 33,500 A is 42,000 A.

The third important requirement (NFPA 70, Article 110.16) is that specific equipment for use other than dwelling units shall be field marked to warn qualified persons of potential arcing hazards.  This includes switchboards, switchgear, panelboards, industrial control panels, motor control centers, and meter socket adapters.  Equipment labels should meet the requirements noted NFPA 70E, Standard for Electrical Safety in the Workplace, and ANSI Z535.4, Product Safety Signs and Labels.  The dangers associated with arc hazards are well documented. There are many changes that have been introduced and I will discuss those in more detail in the coming months.

Where I still see gaps related to electrical safety is ensuring that equipment is installed in accordance with the manufacturer’s requirements, and ensuring that the equipment has a SCCR that is equal to or greater than the short circuit (fault) current at the point of installation.  

If equipment is not installed properly and within its rating, then the foundation of electrical safety is on shaky ground.  Like any program, starting with a solid foundation provides the opportunity to be successful.  Ensuring that equipment is installed in accordance with the requirements detailed in the National Electric Code (NFPA 70) provides the solid foundation to ensure that your electrical safety program is successful.

If you have questions equipment design or installation, or issues related to electrical safety, send me an e-mail at cole3250@gmail.com.

The Trilogy of Electrical Safety

There are a number of changes that have been introduced in 2014 that will affect people working on or near exposed live (energized) circuits.  Over the next couple of months, I will explain a few of the most important changes detailed in NFPA 70E.  In general, the 2015 edition of The Standard for Electrical Safety in the Workplace (NFPA 70E) reflects changes that make sense.

Before looking at the details, one must consider a holistic approach to safety to obtain a complete picture.  There are three standards that affect the interaction of people with electrical hazards.  These are the National Electric Code (NFPA 70), The Standard for Electrical Safety in the Workplace (NFPA 70E), and Recommended Practice for Electrical Equipment Maintenance (NFPA 70B).  To workplace free from electrical hazards, one needs to make sure that all three standards are used.

The National Electric Code (NEC) provides the basic requirements to ensure that equipment is installed properly.  The NEC describes the “normal” operation of equipment.  When equipment is designed and installed in accordance with the NEC, at that point there is minimal potential electrical hazards: shock hazards or arcing hazards.  For example, an electrical panel installed in accordance with the articles in NFPA 70 Chapter 408 does not present a shock or arc flash hazard when the deadfront covers are properly installed. 

The Recommended Practice for Electrical Equipment Maintenance standard provides the basic requirements for properly maintaining equipment.  This includes the development of an electrical preventative maintenance (EPM) program and recommended practices for equipment and conductors.  NFPA 70B provides the requirements after the equipment has been installed and operated, and subsequently temporarily removed (de-energized) from service for maintenance.  For example, an electrical panel has been de-energized, locked out and tagged out, and is undergoing examination and testing of the panelboard itself, the internal molded case circuit breakers (MCCBs), and the conductors entering and exiting the panelboard.

The Standard for Electrical Safety in the Workplace provides the basic requirements for working on equipment in an “abnormal” condition.  It is an abnormal condition as the equipment is not being used as intended nor is it being maintained.  For example, an electrical panelboard undergoing voltage testing to determine if circuits are operating properly is an abnormal condition.  In this scenario, the deadfront covers are removed and personnel are exposed to live (energized) parts.  Because there is an interaction with exposed live (energized) circuits, there is a shock hazard risk and an arc flash hazard risk.

Many consider that the safety of personnel from shock and arc flash hazards are only associated with the practices detailed in The Standard for Electrical Safety in the Workplace.  However, this is not true.  Safety from electrical hazards starts with the proper installation of equipment, followed by the proper servicing and maintenance of the equipment.  When the equipment is properly installed and maintained, then qualified personnel following safe work practices and using proper personal protective equipment (PPE) can work on exposed live (energized) circuits under specific conditions.

Working IN Safety v. Working ON Safety – An Equipment Design Perspective

2014 was a very busy and exciting year for me.  I have helped a number of people and organizations this year in the control of hazardous energy (lockout tagout), lab equipment design, safety review of equipment.  Additionally, I have trained more than 300 people in basic electrical safety (including shock and arc flash hazards), arc flash hazard analysis, and electrical equipment design.

While I was putting together my plan for blog postings this year, I ran across a LinkedIN posting on “WorkingIn Safety v. Working On Safety” [1] that I thought was very informative and timely.  When we work in safety we are performing specific tasks.  Working IN Safety includes working on risk assessments, evaluating equipment to safety standards, performing functional safety testing, etc.

In contrast, Working ON Safety requires setting goals, establishing processes and procedures to ensure that the organization has the capabilities to meet the established goals.  This includes having the appropriate personnel and resources are dedicated to meet the established goals.

Goals should be established using the SMART system are:

• Specific
• Measureable
• Attainable
• Relevant
• Time bound

Organizations that design, manufacturer, or sell equipment should have an organization goal of ensuring that the equipment designed or sold in 2015, when used in accordance with the defined operating conditions, does not create any hazards that would result in more than minor first aid.  The establishment of the aforementioned goal is more than ensuring that their products meet the defined safety requirements (National Electric Code or UL Standards).

For safety leaders, Working ON Safety in meeting this goal can include:

• Obtaining and training the appropriate personnel
• Ensuring that sufficient financial resources are available
• Incorporation of equipment safety personnel into the design, development, manufacturing processes
• Defining the methodologies that will be used to determine the safety of the equipment
• Risk assessments
• Failure Modes Effects Analysis (FMEA)
• Process FMEA
• Defining, developing, and establishment of an equipment validation and verification process
• Creation of Product Safety review process

Organizations that design, manufacturer, or sell equipment play an important component in determining if people are injured while working.  Safety leaders who spend time Working ON Safety will play a pivotal role ensuring that ALL workplace injuries are reduced.

I hope everyone has a successful, prosperous and SAFE year! 

Reference:

1. http://www.safetycultureexcellence.com/e/working-in-safety-vs-working-on-safety/

Comparing An Arc Flash Hazard Analysis to An Alternative Approach [NFPA 70E Table 130.7(C)(15)]

My topic on how often you are required to conduct an Arc Flash Hazard Analysis has opened some eyes of facility engineers and those responsible for electrical safety (e.g. Safety Managers).  Many organizations have the resources, either financial or manpower, to conduct an Arc Flash Hazard Analysis.  However, there are some organizations that do not have those resources.

Luckily, the Standard for Electrical Safety in Workplace (NFPA 70E) provides some guidance for those organizations that need an alternative approach to conducting an Arc Flash Hazard Analysis.  NFPA 70E, Article 130.5 requires an Arc Flash Hazard Analysis be conducted and that analysis shall be reviewed and/or updated every five years or whenever a major modification occurs [1].  There is an exception that allows for the use of NFPA 70E Table 130.7(C)(15) and Table 130.7(C)(16) be permitted instead of conducting an Arc Flash Hazard Analysis to determine what protective methods are to be used by Qualified Employees who are working on or near exposed live (energized) circuits [1].

Table 130.7(C)(15) provides a description of various tasks for particular energized equipment and provides corresponding levels of arc flash personal protective equipment (PPE), whether or not insulated gloves (for shock protection) are required, and whether or not insulated tools are required.  Table 130.7(C)(16) provides a description of the levels of arc flash PPE.

The advantage of using Table 130.7(C)(15) and Table 130.7(C)(16) is that it can be easier to determine the PPE requirements for a particular task and location as compared to the arc flash hazard analysis.  When using these tables the notes associated with each section shall be followed.  This requires that the short circuit current and the opening time of the upstream overcurrent protective device be determined.  In many cases, this will require an engineer to conduct the evaluation.

The disadvantage of using the Table 130.7(C)(15) and Table 130.7(C)(16) is that this method can result in a more conservative level of PPE required for working on or near exposed live (energized) circuits than what would be required if an arc flash hazard analysis was conducted.  Additionally, if the short circuit current (SCC) or the opening time of the overcurrent protective device exceeds the values denoted in the notes of the table in NFPA 70E, then the tables cannot be used.  This condition would then require an arc flash hazard analysis.

Probably the best way to show the limitations of Table 130.7(C)(15) and Table 130.7(C)(16) is through an example.

This example will determine the incident energy, the arc flash boundary, the Class of Shock Hazard PPE, and the Category of an Arc Flash Hazard PPE at point FA, the power control cabinet.  The example will compare the data obtained from performing an arc flash hazard analysis to using the tables in NFPA 70E.

The SLD is shown in Figure A1.  A 2 MVA transformer steps down utility power voltage, sourced from a 20 MVA substation located 1 mile away, from 34.5 kV to 480Y/277 three-phase, 4W+G.  The impedance of the transformer is five percent.  The output of the transformer supplies two 480 V circuits through circuit breakers CB1 and CB2 located 10 feet away by two 1000 MCM conductors paralleled per phase (C1).  Circuit breaker CB2 is connected to a power control cabinet by fifty feet of # 4/0 AWG conductor.  The power control cabinet is protected by a 200 A thermal-magnetic circuit breaker (CB3) with shunt trip capability.

Through a short circuit current study, the short circuit current at location FA is 42,300 A and the calculated arcing current is 19,760 A.  The bolted fault power is 35.2 MVA.  The clearing time of circuit breaker CB2 is 0.1 seconds.

The calculation for the Flash Protection Boundary can be accomplished using EQ1.

where D_FPB is the flash protection boundary in feet, MVA_BF is the bolted fault power, voltage and current (applicable between 16,000 A and 50,000 A), and t is the duration of the fault (less than 0.6 seconds).

The calculation for the Incident Energy at 18 inches can be accomplished using EQ2.

where E_INC is the incident energy in Calories/cm², FA is the short circuit current (fault current) in kilo-amperes (applicable between 16,000 and 50,000 A), and t is the duration of the fault in seconds.

Performing the arc flash hazard analysis utilizing the above information, EQ1 and EQ2 yields a Flash Protection Boundary of 3.1 inches, and an Incident Energy of 11.7 calories/cm².  Based on these calculations, the PPE level required for the Power Control Cabinet is Category 3.

A summary is of the Arc Flash Hazard Analysis is shown in Figure A2:

As noted, an alternative to conducting an arc flash hazard analysis is to use Table 130.7(C)(15(a) from NFPA 70E.  Using NFPA 70E Table 130.7(C)(15)(a), the applicable task is “Panelboards or Other Equipment Rated > 240 V and up to 600 V”.  The particular applicable section is “Work on energized electrical conductors and circuit parts of utilization equipment feed directly by a branch circuit breaker of a panelboard”.

The notes indicate that the maximum short circuit current is 25,000 A, the maximum clearing time is 0.03 seconds (2 cycles) and the minimum working distance is 18 inches.  In this case, Table 130.7(C)(15(a) cannot be used as the short circuit current and the trip time exceeds the limiting parameters.  Trying to use Table 130.7(C)(15)(a) when the short circuit current and/or the trip time of the overcurrent protective device exceeds the amplitudes and/or duration stated in the notes can result in incident energy that exceeds the level of PPE stated.  This can create a hazardous condition that could result in an injury as severe as not wearing any PPE at all.