ES&H Manual --> Volume II: Health & Safety--Hazards and Controls -->
Part 4: Electrical


Source Document:
LLNL's Health & Safety Manual


Electrical Safety

Contents of Chapter 23

23.1 Introduction

23.2 Hazards

23.3 Controls for Electrical Work and Electrical Equipment

23.3.1 General
23.3.2 Electrical Equipment Conditions of Approval and Use
23.3.3 Work on Electrical Components and Systems
23.3.4 Clearances and Illumination for Electrical Enclosures
23.3.5 Temporary Wiring
23.3.6 Extension Cords/Multiple Outlet Boxes/Flexible Cords and Cables
23.3.7 Power Plugs and Receptacles
23.3.8 Ground-Fault Circuit Interrupters
23.3.9 Portable Electrical Tools, Equipment, and Instruments
23.3.10 Equipment Grounding
23.3.11 Static Electricity
23.3.12 Personal Protective Equipment
23.3.13 Reviews and Inspections
23.3.14 Emergency Assistance and Rescue
23.3.15 Minor Shocks
23.3.16 Analysis of Electrical Incidents
23.3.17 Specific Training
23.3.18 Supplementary Training

23.4 Responsibilities

23.4.1 Employees
23.4.2 Supervisors
23.4.3 Electrical Safety Advisory Board

23.5 Work Standards

23.6 Resources for More Information

23.6.1 Contacts
23.6.2 Lessons Learned
23.6.3 Other Sources

Appendix 23-A Terms and Definitions

Appendix 23-B Effects of Electrical Energy on Humans

23.1 Introduction

This document contains general requirements for all Laboratory work involving the use of electrical equipment and systems. Appendix 23-A contains terms and definitions and Appendix 23-B, the effects of electrical energy on humans. All managers, designers, users, installers, and others who service or operate electrical equipment--including those used for research and development (R&D)--shall comply with these requirements.

More specific information about electrical work can be found in "Work and Design Practices for Electrical Equipment" (H&SM S23.01) and "AHJ Policies and Requirements for Approving Electrical Equipment, Installation, and Work" (H&SM S23.02) in Volume II of the Environment, Safety, and Health (ES&H) Manual. In addition, Laboratory programs may consult the Electrical Safety Advisory Board (ESAB) for further guidance on electrical work. The ESAB was chartered on February 20, 1996, and is the Laboratory's technical resource for electrical safety issues. The Board comprises a chair and several members from Hazards Control, Electronics Engineering, Scientific Programs, and Plant Engineering who are knowledgeable in electrical safety. The chair is a member of the Technical Support and Policy Development Division and is appointed by the Hazards Control Department Head. The other members are nominated by the chair and approved by the Hazards Control Department Head.

23.2 Hazards

Electricity is used in many different ways at LLNL. Each application has its own combination of hazards that includes the potential of electric shock, fire, and burns. Thus, it is essential for all employees, including supplemental labor and subcontractor employees, to be aware of the hazards associated with electrical work and use appropriate protective methods to minimize the risk of an injury or accident.

Appendix 23-B contains more detailed information about the effects of electrical energy on humans.

23.3 Controls for Electrical Work and Electrical Equipment

23.3.1 General

Only qualified and authorized individuals are permitted to perform electrical work at LLNL. A qualified person is one who has the required skills and knowledge to perform electrical work safely. Such individuals must be aware of the hazards associated with electrical work (see Appendix 23-B for details) and the methods for reducing the risk of electrical accidents that can result from unsafe equipment, adverse environmental conditions, and unsafe acts.

Whenever possible, all circuits or equipment shall be de-energized before beginning any work. Work on energized circuits shall only be performed by authorized workers, as described in H&SM S23.01. In addition, these workers shall use

In support of Lab-wide electrical safety, management shall take a proactive approach when dealing with the root causes of employees' concerns, near-misses, and incidents or accidents involving electrical hazards.

23.3.2 Electrical Equipment Conditions of Approval and Use

All electrical equipment, components, and conductors should be listed, labeled, and approved by an NRTL for their intended purpose. Custom-made and installed equipment can be approved for use, by the Electrical Authority Having Jurisdiction (AHJ), if built according to specific standards (e.g., Underwriters Laboratories [UL] 508 or one of the ANSI C series standards). Appropriate documentation for such equipment shall be maintained on file.

When building, repairing, or modifying electrical systems, NRTL-approved equipment must be used if available. Non-NRTL-approved equipment (e.g., shop-made extension cords) shall be built in accordance with an approved design, as specified in H&SM S23.02.

23.3.3 Work on Electrical Components and Systems

Any live electrical parts shall be positively de-energized when working on or near electrical circuits, equipment, or systems. Circuits and equipment must be considered energized until isolated, locked out and tagged , and verified with an appropriate testing device as described in "Lockout and Tag Program" (H&SM S26.13) in Volume II of the ES&H Manual. Where it is possible for the circuits to be energized by another source, or where capacitive and/or inductive devices (including cables) may retain or build up a charge, circuits shall be grounded and shorted. Exceptions to this paragraph may be permitted when the requirements in H&SM S23.01 are fulfilled.

Additionally, the following precautions shall be observed to improve safety in the workplace:

23.3.4 Clearances and Illumination for Electrical Enclosures

A clear working space shall be maintained in the front, back, and on each side of all electrical enclosures and around electrical equipment for safe operation and to permit access for maintenance and alteration. Refer to the documents listed in this section as required. (NOTE: The National Electrical Code (NEC) is available from the Technical Information Department (TID) Library and the Plant Engineering Library. You may also contact Hazards Control for additional information about the NEC):

In addition to the NEC, the IES Lighting Handbook (latest edition) specifies the following requirements for electrical equipment:

23.3.5 Temporary Wiring

Construction Power and Lighting. Temporary wiring for electric power and lighting is permitted during periods of construction, remodeling, maintenance, repair, or demolition of equipment or structures and during emergencies. Temporary wiring does not mean a "reduced" level of safety or quality, as this wiring must still conform to certain criteria for electrical work.

Temporary wiring shall have a temporary wiring tag attached to it with the following information:

In addition, temporary wiring

Switches or other means shall be installed to permit the disconnection of all ungrounded conductors of each temporary circuit. All lamps used for temporary illumination shall have a suitable fixture or lamp holder with a guard to prevent damage or accidental contact with energized parts.

Experiments. Temporary wiring may be used for experimental and developmental equipment. There is no time limit on how long the wiring can remain in place, except that it must be removed upon completion of the experiment. Temporary wiring tags are not required for temporary wiring within experimental systems. However, they are required for the power feeder to the power distribution points of experimental systems. The wiring tag on these systems shall contain the same information as previously described.

23.3.6 Extension Cords/Multiple Outlet Boxes/Flexible Cords and Cables

Extension Cords. Observe the following precautions when using extension cords. Note that extension cords for normal office use do not require a temporary wiring tag.

Only high-visibility orange or yellow extension cords shall be used outdoors and with portable or integral ground-fault circuit interrupters (GFCIs).

Multiple Outlet Boxes. Observe the following precautions when using multiple outlet boxes:

Note that multiple outlet boxes used in offices, as well as those used to provide surge protection for computers, do not require a temporary wiring tag.

Flexible Cords and Cables. Flexible cords and cables shall comply with the requirements in NEC Article 400 (Flexible Cords and Cables). They shall not be

Individual conductors of a flexible cord or cable shall not be smaller than those listed in Table 400-5(A) and (B) of NEC Article 400.

Article 240-4 of the NEC (Protection of Flexible Cords and Fixture Wires) states that flexible cords, including extension cords, shall be protected against overcurrent in accordance with their amperage ratings (see Tables 400-5(A) and 400-5(B)). NEC Article 400-14 states that flexible cords and cables inserted through holes in covers, outlet boxes, or similar enclosures shall be protected by bushings or fittings.

23.3.7 Power Plugs and Receptacles

The Laboratory uses many different voltages, frequencies, and current (ac or dc) in power systems and equipment. Thus, it is essential to ensure that such equipment cannot be inadvertently connected to the wrong power source. For specific purposes, voltage, and current ratings, use a plug or receptacle that fully complies with the requirements in ANSI C73. See the configuration chart (from ANSI C73) in the NFPA National Electrical Code Handbook for information about general-purpose locking and nonlocking plugs and connectors. Use of the National Electrical Manufacturers Association (NEMA) connectors may not be appropriate for all research and development applications. Contact Electronics Engineering Specifications and Standards Group for guidance, if necessary.

23.3.8 Ground-Fault Circuit Interrupters

Ground-fault circuit interrupters-either circuit breakers or portable ground-fault interrupting receptacles-shall be used for

Unlike fuses or standard circuit breakers, which are designed to protect equipment from overcurrent, GFCIs are designed to protect personnel from serious injury or death.

Article 305-6 of the NEC (Ground-Fault Protection for Personnel) requires GFCI protection of all 125 V, single phase, 15, 20, and 30-Amp receptacles that are associated with temporary wiring on construction sites. LLNL requires the use of GFCIs for any type of construction work to ensure personnel protection, even if the receptacle is part of the permanent wiring of the building.

Laboratory practice is to provide its employees and subcontractors with at least the same level of protection from electric shock as they would have in their own homes. NEC Article 210-8 (Ground-Fault Circuit-Interrupter Protection for Personnel) specifies that GFCIs must be installed in the following locations:

Thus, all the aforementioned areas within LLNL shall have receptacles with GFCI protection.

Exceptions to these requirements are:

23.3.9 Portable Electrical Tools, Equipment, and Instruments

Portable electrical equipment or tools shall always be inspected to identify defects; defective equipment shall be removed from service immediately. Portable electrical equipment shall be connected to a portable GFCI (or a circuit that contains a GFCI) when used outdoors, in damp locations, in any unsafe environment, or for indoor or outdoor construction. Ordinarily, the casings for portable electrical equipment are grounded. If it is necessary to operate this type of equipment with other than a grounded equipment casing, suitable barriers, guards, or shields shall be installed to protect personnel while working on or near the equipment. In addition, a safety procedure shall be written describing the controls for safe operation of the equipment.

Receptacles and flexible cords can be used to connect electrical appliances and equipment (e.g., fans, machine tools, and pumps) to power sources. Receptacles used on a two-wire, single-phase portable generator (or vehicle-mounted generator) with a rating of not more than 5 kW (where the circuit conductors are insulated from the frame and all other grounded surfaces) do not need to be GFCI protected.

23.3.10 Equipment Grounding

All electrical apparatus, equipment, and systems shall be grounded in accordance with NEC Article 250 (Grounding) and ANSI standards. The conductor used for grounding shall meet the following criteria:

Guidelines for proper grounding of programmatic equipment and systems can be found in the Electronics Engineering Department Grounding Guidelines: Practical Examples for Power Systems at LLNL (UCID-19752).

23.3.11 Static Electricity

A static charge is an imbalance of electrons on objects (matter) that can build up on all matter and transfer from one object to another by conduction or induction. The discharge of static electricity can cause shock or a fire or explosion. Although this type of shock is painful, it is not normally physically hazardous and therefore is not considered reportable as an electric shock. It should be noted, however, that injuries may result from reaction to the shock (i.e., by a person rapidly pulling his/her hand away from a metal object and hitting an elbow against a wall or cabinet).

Equipment and Personnel Guidelines. When working with electrical equipment, employees shall follow the guidelines below for their own protection and that of the equipment:

NFPA Regulations for Fire and Lightning. NFPA 77 (Static Electricity) contains requirements for reducing the fire hazard of static electricity. Lightning, an example of static electricity, is covered in NFPA 78 (Lightning Protection Code). This document gives lightning protection requirements for ordinary facilities and for facilities containing flammable vapors, gases, or liquids.

Flammable Vapor. A flammable vapor source can be ignited by static electricity if the following conditions exist simultaneously:

Liquids. Electrostatic charges can be generated by the movement of liquid through pipes, funnels, pumps, filters, or by free-flowing through air. Static charges generated by flowing liquids can be reduced or eliminated by bonding or grounding, or both; by lowering the flow rate; or by reducing the amount of misting, spraying, free-fall, and splashing of the liquid. Pay particular attention to situations where the liquid stream may impinge on a connection to a capacitor, high-voltage bushing, or cable terminal. Static charge from the liquid can store hazardous quantities of electrical energy in a capacitor over time. This hazard is most likely to occur when filling electronic apparatus tanks with insulating oil.

23.3.12 Personal Protective Equipment

Personal protective equipment is required when installing, examining, adjusting, servicing, fabricating, testing, or maintaining electrical equipment. The work supervisor shall provide employees with the appropriate PPE, and shall ensure that the equipment is used properly. Alternatively, employees may contact the area ES&H Team for assistance in selecting the appropriate PPE for the operation. Protective footwear; hard hats; and insulated, nonmetallic-framed safety glasses shall meet the requirements of ANSI Z41, ANSI Z87.1, and ANSI Z89.2 (see Table 23-1 below).

Rubber-insulated (nonconductive) protective equipment shall be visually inspected at the beginning of each workday before use and after performing work that can cause damage to PPE. This inspection shall include an air test of the gloves used. Hot sticks, grounds, aerial-lift equipment and booms, hot rope, and hot ladders shall also be visually inspected.

23.3.13 Reviews and Inspections

Major modifications to new and existing facilities and projects may be inspected by the DOE (or authorized designee) to verify compliance with codes and standards in effect on the day that such work is approved by a final design review. If the modification involves a hazard to life, equipment, or property, current safety requirements shall be reviewed and used to mitigate the hazard.

Table 23-1. ASTM/ANSI standards for PPE.
Protective equipment or apparel ASTM
Rubber, insulating gloves D 120 --
Rubber, insulating matting D 178 --
Rubber, insulating blankets D 1048 --
Rubber, insulating covers D 1049 --
Rubber, insulating line hose D 1050 --
Rubber, insulating sleeves D 1051 --
Protective foot wear -- Z41
Eye and face protection -- Z87.1
Nonconductive hard hats (helmets) -- Z89.2
Leather protectors for rubber insulating gloves F 696 --

23.3.14 Emergency Assistance and Rescue

Anyone who witnesses or discovers a serious electric shock that results in any of the conditions listed below, at the Livermore site or at Site 300 shall immediately call the Fire Department Emergency Rescue (dial 911) (from a cell-phone, call 925-447-6880).

  1. Obvious serious injury (e.g., loss of consciousness, significant trauma).

  2. Altered mental status (e.g., confusion, slow/slurred speech).

  3. Other obvious injury (e.g., laceration, muscle strain, burn).

In addition to calling 911:

Refer to "Occupational Medical Program" (H&SM C5) in Volume IV of the ES&H Manual for additional information.

23.3.15 Minor Shocks

All other electric shock victims must be taken to Health Services for evaluation so that potentially damaging effects can be detected early and treated properly. It should be noted that such effects may not be immediately recognized and can appear later (see Appendix 23-B for details). Do not let the shock victim drive himself to Health Services.

23.3.16 Analysis of Electrical Incidents

Serious and potentially lethal incidents, including near misses that could result in a serious or potentially lethal shock, shall undergo an incident analysis in accordance with "Incidents-Notification, Analysis, and Reporting" (H&SM C4) in Volume I of the ES&H Manual. This analysis shall be determined by facility or program management and the responsible ES&H Team.

23.3.17 Specific Training

Electrical Workers. Employees who perform electrical work shall be trained to recognize the hazards associated with their work environment and use appropriate procedures and protective equipment to minimize the risk of an accident or injury. The payroll supervisor provides trained electrical workers. Work supervisors shall verify the qualifications and training of all electrical workers before they are permitted to perform electrical work. Training requirements are identified in the LLNL Training Program Manual and the Directorate Training Implementation Plan.

Employee training shall be documented with respect to the specific equipment and tasks for which the employee is qualified. Much of the experience required for an employee to be considered qualified is specific to the equipment and tasks involved. On-the-job training is always a necessary component of a qualification program. Classroom training, including courses offered by Hazards Control, is a useful way to ensure that employees share a common level of basic knowledge on which to build specific on-the-job training. Additionally, employees can gain knowledge and experience about how to perform their jobs safely and properly by taking courses offered by universities and trade schools or through apprenticeships, on-the-job training (OJT), or other formalized training. The depth of training and how training is provided shall be determined by the hazards associated with the employee's respective tasks.

Electrical workers shall be trained in and familiar with the following subject areas:

Hazards Control offers the following courses to fulfill some of these requirements:

Refresher training for electrical workers is required at intervals listed in the course catalog, and shall include a formal review of current regulations and safety practices.

Electrical workers should take HS1620, "Multimedia First Aid with CPR."

Nonelectrical Workers. The Occupational Safety and Health Administration requires training for nonelectrical workers whose job assignments require them to be close to exposed parts of electrical circuits operating at 50 V or more. Hazards Control offers the following course for this purpose:

23.3.18 Supplementary Training

In addition to the courses Hazards Control offers, both electrical and nonelectrical workers whose job assignment requires them to work close to exposed electrical circuits operating at 50 V or more to ground (in accordance 29 CFR 1910.332) should receive supplementary training in the following subject areas:

For additional training requirements, see the LLNL Training Program Manual and the Directorate Training Implementation Plan.

23.4 Responsibilities

The responsibilities of individuals with regard to electrical work are listed below each title.

23.4.1 Employees

23.4.2 Work Supervisors

23.4.3 Electrical Safety Advisory Board

23.5 Work Standards

29 CFR 1910, Subpart S, "Electrical."

29 CFR 1910, Subpart H, "Hazardous Materials."

29 CFR 1910, Subpart J, "General Environmental Controls." (Section 1910.147, "The control of hazardous energy lockout/tagout," specifically applies.)

29 CFR 1910, Subpart R, "Special Industries." (Section 1910.269, "Electrical power transmission, and distribution," specifically applies.)

29 CFR 1910, Subpart I, "Personal Protective Equipment."

29 CFR 1926, Subpart K, "Electrical."

DOE M 440.1-1, DOE Explosives Safety Manual.

DOE O 420.1, Facility Safety Section, "Nuclear Safety Design Requirements," 7, "Implementation Plans."

NFPA 70, National Electrical Code.

23.6 Resources for More Information

23.6.1 Contacts

For additional information about the topics covered this document, contact the following:

23.6.2 Lessons Learned

For lessons learned specific to electrical work areas or electrical equipment, refer to the following web site:

23.6.3 Other Sources

29 CFR 1910.268, "Telecommunications."

29 CFR 1926, Subpart V, "Power Transmission and Distribution" (latest edition).

ANSI C73, "American National Standard on Dimensions of Attachment Plugs" [configuration tables for general-purpose nonlocking and locking plugs and receptacles].

ANSI C84.1, "For Electric Power Systems and Equipment-Voltage Ratings (60 Hz)."

ANSI/IEEE Standard 18, "IEEE Standard for Shunt Power Capacitors."

ANSI/IEEE 80, "IEEE Guide for Safety in AC Substation Grounding."

ANSI/IEEE C2, "National Electrical Safety Code" (latest edition)."

ANSI/ISA-S82.01, .02, and .03, "Safety Standard for Electrical and Electronic Test, Measuring, Controlling and Related Equipment."

ANSI Z136.1, Section 7, "ANSI Standard for the Safe Use of Lasers" [Subsection 7.4, "Electrical Hazards."]

Charles F. Dalziel, "The Effects of Electric Shock on Man," Industrial Radio Engineers Transactions on Medical Electronics (May 1956).

DOE/EV/0051/1, Electrical Safety Requirements for R&D Activities.

DOE-HDBK-1092-98, Electrical Safety Handbook.

Electronics Engineering Department, Grounding Guidelines: Practical Examples for Power Systems at LLNL, Lawrence Livermore National Laboratory, Livermore, CA (UCID-19752).

FIPS PUB 94, "Guideline on Electrical Power for Automatic Data Processing Installations."

IEEE 450-IEEE, "Recommended Practice for Maintenance, Testing, and Replacement of Large Lead Storage Batteries for Generating Stations and Substations."

Illuminating Engineering Society, IES Lighting Handbook (latest edition).

NETA, International Electrical Testing Association, Inc., "Acceptance Testing Specifications for Electric Power Distribution Equipment and Systems."

NFPA 70B, Electrical Equipment Maintenance.

NFPA 70E, Electrical Safety Requirements for Employee Workplaces (latest edition).

NFPA 75, Electronic Computer/Data Processing Equipment.

NFPA 77, Recommended Practice on Static Electricity.

NFPA 78, Lightning Protection Code (latest edition).

NFPA 79, Electrical Standard for Industrial Machinery National Fire Protection Association (interpretations of current NFPA 70).

NFPA 110, A-Stored Electrical Energy Emergency and Standby Power Systems."

Ralph H. Lee, "Human Electrical Sheet" while an IEEE Fellow at E. I. duPont de Nemours & Co.; and "Electrical Safety in Industrial Plants," in IEEE Spectrum, June 1971.

Appendix 23-A

Terms and Definitions

The following terms and acronyms are used in this document and the supporting appendices.

Affected employee
Any employee (including subcontractors) whose job requires him/her to operate or use a machine or work in an area where service or maintenance of equipment is being performed.

Alternating current.

American National Standards Institute.

Authority having jurisdiction (AHJ)
An individual who interprets the requirements of all electrical codes and standards such as the National Electrical Code (NFPA 70); the National Electrical Safety Code (ANSI/IEEE C2); 29 CFR 1910, Subpart S; 29 CFR 1926, Subparts K and V; and H&SM S23.02. This individual also approves electrical equipment, wiring methods, electrical installations, and utilization of equipment for compliance.

Authorized person
Any employee (including subcontractors) with acquired skills and training who has been approved or assigned by the supervisor to perform specific work or tasks.

The permanent joining of metallic parts to form an electrically conductive path that will ensure electrical continuity and the capacity to conduct safely any current likely to be imposed.

Code of Federal Regulations.

Competent person
A person who is (1) capable of identifying existing and predictable hazards in workplaces; and (2) authorized and qualified by management to take prompt corrective measures to eliminate hazards, provide first aid, and notify the appropriate personnel when an accident or incident occurs.

Cardiopulmonary resuscitation.

Dead-front construction
Electrical equipment built so that, in NEC 70 Article 100's definition, it is "without live parts exposed to a person on the operating side of the equipment." Article 384 (Switchboards and Panel Boards), in paragraph 384-3.(a), requires that "barriers shall be placed in all service switchboards that will isolate the service bussbars and terminals from the remainder of the switchboard."

Direct current.

Electrical equipment
A general term for material, fittings, devices, appliances, fixtures, apparatus, and the like that are used as a part of or in connection with an electrical installation. The term applies to both power-generation equipment and electronics equipment.

Electrical hazard
Any situation in which an employee or any conductive tool or object in contact with the employee could contact or approach closer than the safe clearance distance of any live part or other energized conductor. Any situation in which electrical equipment is likely to cause a fire because of defective components or design. Examples of electrical hazards include inadequate working clearance while working on energized circuits, exposed energized parts, electrical equipment inadequately guarded or enclosed, electrical equipment in an unsafe environment, and unsafe electrical equipment. Generally, electrical equipment that is not in compliance with OSHA regulations or NEC standards presents a potential hazard.

Electrical worker
An electrical worker is a person trained, qualified, and authorized to work on electrical equipment. He/she is usually hired specifically for this purpose.

Facility power
Main disconnects, panel boards, switches, and associated wiring are considered facility/building power and are typically less than 600 V ac. These systems are designed and installed to operate facilities in these buildings (i.e., lighting, heating, air conditioning, or standby power supply and circuitry).

Facility Safety Plan.

Ground-fault circuit interrupter.

Connected to earth or to some conducting body that serves in place of the earth. Physically and intentionally connected to the earth through a ground connection of sufficient low impedance and with sufficient current-carrying capacity to prevent the buildup of voltages that may result in undue hazard to connected equipment or persons. (See ungrounded.)

Joule (J)
Watt-second (power x time); a unit of energy.

Equipment or materials to which a label, symbol, or other identifying mark has been applied by an NRTL.

Equipment or materials included in a list published by an NRTL.

Live/energized parts
The current edition of 29 CFR 1910 defines a "live part" as an electrically conducting part carrying more that 50 V ac or dc. (A part may be designated as "not live" if the current from the part to ground through 1500 ohms non-inductive resistance shunted by a capacitance of 0.15 f cannot exceed 0.5 mA, even though the part carries voltage equal to or greater than that specified for a live part.)

Lockout and tag procedure
LLNL's general procedure for affixing appropriate locks and tags to energy-isolating devices to prevent inadvertent energizing or start-up of machines or equipment while service and maintenance is being performed. Lockout devices prevent the release of energy that could cause injury or death. Refer to H&SM S26.13 for details on this procedure.

Minimum work distance or clearance
A minimum separation distance between a qualified electrical worker (or any conducting object touching the worker) and any energized component. Also, a mandatory separation distance between any energized component and vehicles or machinery. See H&SM S23.01, 29 CFR 1910.303, and 29 CFR 1910.304.

National Electrical Code.

National Electrical Manufacturers Association.

National Fire Protection Association.

Nationally recognized testing Laboratory (NRTL)
An organization that is concerned with product evaluation and maintains periodic inspection of listed equipment and materials. The NRTL ensures that the equipment or materials meet appropriate designated standards and that they have been tested and found to be suitable for use in a specified manner. (Refer to 29 CFR 1910.7, "Definition and Requirements for a Nationally Recognized Testing Laboratory.")

Nominal system voltage
A nominal value assigned to a circuit or system to conveniently designate its voltage class (e.g., 120/240 V, 480Y/277 V, 600 V). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of the equipment. (Refer to ANSI C84.1, "Electric Power Systems and Equipment--Voltage Ratings [60 Hz]" for details.)

On-the-job training.

Occupational Safety and Health Administration.

Operational Safety Plan.

Personal protective equipment.

Qualified person
A person who has been determined by his/her supervisor to have the skills, knowledge, and abilities to safely perform the work to which he/she is assigned. Qualifications may include a recognized degree, certificate, or professional standing--through extensive knowledge, training, and experience--or that one has successfully demonstrated the ability to resolve problems relating to the subject matter or work to the satisfaction of his/her supervisor.

Safety watch
A person specifically assigned to stand by (within visible and audible range of workers) and continually monitor equipment and personnel for safety.

Strain relief
A mechanical device that prevents force from being transmitted to the connections or terminals of a cable.

Temporary wiring
Electrical wiring that is temporarily installed for a limited time to complete a specific task (e.g., construction of a new facility or performance of R&D work). Temporary wiring methods must apply sound engineering practices to ensure adequate electrical safety of temporary wiring installations. Temporary wiring shall conform to the requirements in Section 23.3.5 of this document, Article 305 of the NEC, and the respective subparts of 29 CFR 1910 and 29 CFR 1926.

A condition having no physical connection or continuity with earth ground. A condition of insulation or isolation. (See grounded.)

Utility power
Utility, transmission, and distribution of electrical power systems typically above 600 V ac (i.e., substations, vaults, transformers, switch gear) prior to the final point of transformation and distribution. These electrical systems and equipment then furnish electrical power to buildings and facilities through an electric service entrance. Qualified Plant Engineering personnel (or their designees) are the only individuals authorized to work on these high-voltage systems.

Work supervisor
The person responsible for supervising and directing the work and ensuring the health and safety of workers. Specific responsibilities include

Appendix 23-B

Effects of Electrical Energy on Humans

B.1 Physiological Effects

Electricity flowing through the human body can shock, cause involuntary muscle reaction, paralyze muscles, burn tissues and organs, or kill. The typical effects of various electric currents flowing through the body on the average 150-lb male and 115-lb female body are given in Table 23B-1.

Burns. Although a current may not pass through vital organs or nerve centers, internal electrical burns can still occur. These burns, which are a result of heat generated by current flowing in tissues, can be either at the skin surface or in deeper layers (muscles, bones, etc.), or both. Typically, tissues damaged from this type of electrical burn heal slowly.

Burns caused by electric arcs are similar to burns from high-temperature sources. The temperature of an electric arc, which is in the range of 4,000-35,000F, can melt all known materials, vaporize metal in close proximity, and burn flesh and ignite clothing at distances up to 10 ft from the arc.

Table 23B-1. Effects of electric current on the human body (Ref. 1).
Effect/feeling Direct current
Alternating current (mA) Incident severity
60 Hz 10,000 Hz
150 lb 115 lb 150 lb 115 lb 150 lb 115 lb
Slight sensation 1 0.6 0.4 0.3 7 5 None
Perception threshold 5.2 3.5 1.1 0.7 12 8 None
Shock not painful 9 6 1.8 1.2 17 11 None
Shock painful 62 41 9 6 55 37 Spasm, indirect injury
Muscle clamps source 76 51 16 10.5 75 50 Possibly fatal
Respiratory arrest 170 109 30 19 180 95 Frequently fatal
>0.03-s vent. fibril. 1300 870 1000 670 1100 740 Probably fatal
>3-s vent. fibril. 500 370 100 67 500 340 Probably fatal
>5-s vent. fibril. 375 250 75 50 375 250 Probably fatal
Cardiac arrest -- -- 4000 4000 -- -- Possibly fatal
Organs burn -- -- 5000 5000 -- -- Fatal if it is a vital organ

Delayed Effects. Damage to internal tissues may not be apparent immediately after contact with the current. Internal tissue swelling and edema are also possible.

Critical Path. The critical path of electricity through the body is through the chest cavity. At levels noted in Table 23B-1, current flowing from one hand to the other, from a hand to the opposite foot, or from the head to either foot will pass through the chest cavity paralyzing the respiratory or heart muscles, initiating ventricular fibrillation and/or burning vital organs.

B.2 Biological Effects of Electrical Hazards

Influential Variables. The effects of electric current on the human body can vary depending on the following:

Source Characteristics. An alternating current (ac) with a voltage potential greater than 550 V can puncture the skin and result in immediate contact with the inner body resistance. A 110-V shock may or may not result in a dangerous current, depending on the circuit path which may include the skin resistance. A shock greater than 600 V will always result in very dangerous current levels. The most severe result of an electrical shock is death.

Conditions for a serious (potentially lethal) shock across a critical path, such as the heart, are

  1. More than 30-V root mean square (rms), 42.4-V peak, or 60 V dc at a total impedance of less than 5000 ohms.

  2. 10 to 75 mA.

  3. More than 10 J.

Conditions for a potentially lethal shock across the heart are

  1. More than 375 V at a total body impedance of less than 5000 ohms.

  2. More than 75 mA.

  3. More than 50 J.

The worst possible frequency for humans is 60 Hz, which is commonly used in utility power systems. Humans are about five times more sensitive to 60-Hz alternating current than to direct current. At 60 Hz, humans are more than six times as sensitive to alternating current than at 5000 Hz--and the sensitivity appears to decrease still further as the frequency increases. Above 100-200 kHz, sensations change from tingling to warmth, although serious burns can occur from higher radio-frequency energy.

At much higher frequencies (e.g., above 1 MHz), the body again becomes sensitive to the effects of an alternating electric current, and contact with a conductor is no longer necessary; energy is transferred to the body by means of electromagnetic radiation (EMR). For a discussion on the effects of EMR and the controls required for these sources, refer to "Nonionizing Radiation and Fields" (H&SM S26.12) in Volume II of the ES&H Manual.

Body Impedance. Three components constitute body impedance: internal body resistance and the two skin resistances at the contact points with two surfaces of different voltage potential. One-hand (or single-point) body contact with electrical circuits or equipment will prevent a person from completing a circuit between two surfaces of different voltage potential. Table 23B-2 provides a listing of skin-contact resistances encountered under various conditions. It also shows the work area surfaces and wearing apparel effects on the total resistance from the electrical power source to ground. This table can be used to determine how electrical hazards could affect a worker in varying situations.

Table 23B-2. Human resistance (Q) for various skin-contact conditions (Ref. 2).
Body contact condition Dry (ohms) Wet (ohms)
Finger touch 40,000-1,000,000 4,000-15,000
Hand holding wire 15,000-50,000 3000-5000
Finger-thumb grasp 10,000-30,000 2000-5000
Hand holding a pliers 5000-10,000 1000-3000
Palm touch 3000-8000 1000-2000
Hand around 1.5-in. pipe or drill handle 1000-3000 500-1500
Two hands around 1.5-in. pipe 500-1500 250-750
Hand immersed -- 200-500
Foot immersed -- 100-300

Life-Threatening Effects. Charles F. Dalziel,1 Ralph H. Lee,2 and others have established the following criteria for the lethal effects of electric shock:

The most dangerous current flow via the chest cavity is through the heart when the shock occurs in the time relative to the normal heart rhythm. This current may cause ventricular fibrillation, which is defined as repeated, rapid, uncoordinated contractions of the heart ventricles. Ventricular fibrillation that alters the heart's normal rhythmic pumping action can be initiated by a current flow of 75 mA or greater for 5 seconds (5-s) or more through the chest cavity.

Probability of Ventricular Fibrillation. To determine the 5-s current flow (in mA) necessary to cause a 0.5% probability of ventricular-fibrillation, multiply a person's weight (in lb) by 0.49. To determine the 5-s current flow (in mA) necessary to cause a 99.5% probability of ventricular fibrillation, multiply a person's weight (in lb) by 1.47.

B.3 Determining How Much Current Is Passing through a Body

Use the information in Tables 23B-l through 23B-3 to project how electrical hazards could affect a worker in varying situations when protective equipment and apparel are in series with current flowing through a body. To determine how much current, I, is passing along a body path, use the formula I = E/R. The voltage, E, can be obtained using an appropriate voltmeter. The total body resistance, R, can be determined by combining the appropriate resistance from Table 23B-2 with that from Table 23B-3.

Table 23B-3. Resistance values for equal areas (130 cm2) of
various work-area materials (Ref. 2).
Material Resistance (Q)
Rubber gloves or soles 2.0 x 107
Dry concrete above grade 1.0 x 106 to 5.0 x 106
Dry concrete on grade 2.0 x 105 to 1.0 x 106
Leather sole, dry, including foot 1.0 x 105 to 5.0 x 105
Leather sole, damp, including foot 5.0 x 103 to 2.0 x 104
Wet concrete on grade 1.0 x 103 to 5.0 x 103


  1. Charles F. Dalziel, "The Effects of Electric Shock on Man," Industrial Radio Engineers Transactions on Medical Electronics (May 1956).

  2. Ralph H. Lee, "Human Electrical Sheet" while an IEEE Fellow at E. I. duPont de Nemours & Co.; and "Electrical Safety in Industrial Plants," in IEEE Spectrum, June 1971.

Revision Definitions
Approval date: February 27, 1996
Last minor revision: November 30, 1999

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