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Electrical Safety    from WE DON'T

This article provides WE DON'T fans an overview of basic electrical safety  with electrical hazards. The concepts and principles  presented will help further an understanding of OSHA's electrical safety  standards - Title 29 Code of Federal Regulations (CFR),   Part 1910.302, Sub-part S-Design Safety Standards for Electrical Systems, and  1910.331 Electrical Safety-Related Work Practices Standard (1990).  WE DON'T uses high-voltage equipment every week and has had a few "close calls" over the years.  So now we take our power seriously!

OSHA's electrical  standards address concerns that electricity has long been recognized as a   serious workplace hazard, exposing employees to such dangers as electric  shock, electrocution, burns, fires, and explosions. In 1992, for example, the   Bureau of Labor Statistics reported that 6,210 work-related deaths occurred   in private sector workplaces employing 11 workers or more. Six percent of the   fatalities, or around 347 deaths, were the direct result of electrocutions at   work. What makes these statistics more tragic is that, for the most part,   these fatalities could have been easily avoided.

OSHA'S electrical   standards help minimize these potential hazards by specifying safety aspects in   the design and use of electrical equipment and systems. The standards cover   only those parts of any electrical system that an employee would normally use   or contact. For example, the exposed and/or operating elements of an   electrical installation-lighting, equipment, motors, machines, appliances,   switches, controls, and enclosures-must be constructed and installed so as to   minimize workplace electrical dangers.

For employers and   employees in the 25 states operating OSHA'S approved workplace safety and health   plans, their states may be enforcing standards and other procedures that   while "at least effective" federal standards are not always   identical to federal requirements.

How Electricity Acts

Electricity is   essential to modem life, both at home and on the job. Some employees work   with electricity directly, as is the case with engineers, electricians,   electronic technicians, and power line workers. Others, such as office   workers and sales-people, work with it indirectly. As a source of power,   electricity is accepted without much thought to the hazards encountered.   Perhaps because it has become such a familiar part of our surroundings, it   often is not treated with the respect it deserves.

To handle electricity   safely, it is necessary to understand how it acts, how it can be directed,   what hazards it presents, and how these hazards can be controlled. Operating   an electric switch may be considered analogous to turning on a water faucet.   Behind the faucet or switch there must be a source of water or electricity,   with something to transport it, and with pressure to make it flow. In the   case of water, the source is a reservoir or pumping station; the   transportation is through pipes; and the force to make it flow is pressure,   provided by a pump. For electricity, the source is the power generating   station; current travels through electric conductors in the form of wires;   and pressure, measured in volts, is provided by a generator.

Resistance to the flow   of electricity is measured in ohms and varies widely. It is determined by   three factors: the nature of the substance itself, the length and   cross-sectional area (size) of the substance, and the temperature of the   substance.

Some substances, such   as metals, offer very little resistance to the flow of electric current and   are called conductors. Other substances, such as bakelite, porcelain,   pottery, and dry wood, offer such a high resistance that they can be used to   prevent the flow of electric current and are called insulators.

Dry wood has a high   resistance, but when saturated with water its resistance drops to the point   where it will readily conduct electricity. The same thing is true of human   skin.

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When it is dry, skin   has a fairly high resistance to electric current; but when it is moist, there   is a radical drop in resistance. Pure water is a poor conductor, but small   amounts of impurities, such as salt and acid (both of which are contained in   perspiration), make it a ready conductor. When water is present either in the   environment or on the skin, anyone working with electricity should exercise   even more caution than they normally would.

How Shocks Occur?

Electricity travels in   closed circuits, and its normal route is through a conductor. Electric shock   occurs when the body becomes a part of the electric circuit. The current must   enter the body at one point and leave at another. Electric shock normally   occurs in one of three ways. Individuals-while in contact with the ground-   must come in contact with both wires of the electric circuit, one wire of an   energized circuit and the ground, or a metallic part that has become   "hot" by contact with an energized conductor.

The metal parts of   electric tools and machines may become energized if there is a break in the   insulation of the tool or machine wiring. The worker using these tools and   machines is made less vulnerable to electric shock when there is a   low-resistance path from the metallic case of the tool or machine to the   ground. This is done through the use of an equipment grounding conductor- a   low-resistance wire that causes the unwanted current to pass directly to the   ground, thereby greatly reducing the amount of current passing through the   body of the person in contact with the tool or machine. If the equipment   grounding conductor has been properly installed, it has a low resistance to   ground, and the worker is protected.

Severity of the Shock

The severity of the   shock received when a person becomes a part of an electric circuit is   affected by three primary factors: the amount of current flowing through the   body (measured in amperes), the path of the current through the body, and the   length of time the body is in the circuit. Other factors that may affect the   severity of shock are the frequency of the current, the phase of the heart   cycle when shock occurs, and the general health of the person.

The effects of electric   shock depend upon the type of circuit, its voltage, resistance, current,   pathway through the body, and duration of the contact. Effects can range from   a barely perceptible tingle to immediate cardiac arrest. Although there are   no absolute limits or even known values that show the exact injury from any   given current, the table shows the general relationship between the degree of   injury and amount of current for a 60-cycle hand-to-foot path of one second's   duration of shock.

The table also   illustrates that a difference of less than 100 milliamperes exists between a   current that is barely perceptible and one that can kill. Muscular   contraction caused by stimulation may not allow the victim to free himself or   herself from the circuit, and the increased duration of exposure increases   the dangers to the shock victim. For example, a current of 100 milliamperes   for 3 seconds is equivalent to a current of 900 milliamperes applied for .03   seconds in causing ventricular fibrillation. The so-called low voltages can   be extremely dangerous because, all other factors being equal, the degree of   injury is proportional to the length of time the body is in the circuit. LOW   VOLTAGE DOES NOT IMPLY LOW HAZARD!

A severe shock can cause considerably more damage to the body than is visible. For example, a   person may suffer internal hemorrhages and destruction of tissues, nerves,   and muscles. In addition, shock is often only the beginning in a chain of   events. The final injury may well be from a fall, cuts, burns, or broken   bones.

Effects of Electric Current in the Human Body

Current

Reaction

1 Milliampere

Perception level. Just   a faint tingle.

5 Milliamperes

Slight shock felt; not   painful but disturbing.    Average individual can let go. However, strong involuntary reactions to   shocks in this range can lead to injuries.

6-25 Milliamperes   (women)

Painful shock, muscular control is lost.

9-30 Milliamperes (men)

This is called the freezing current

50-150 Milliamperes

Extreme pain,   respiratory arrest, severe muscular contractions.*    Individual cannot let go. Death is possible.

1,000-4,300   Milliamperes

Ventricular   fibrillation. (The rhythmic pumping action of the heart ceases.) Muscular   contraction and nerve damage occur. Death is most likely.

10,000-Milliamperes

Cardiac arrest, severe   burns and probable death.

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*If the extensor   muscles are excited by the electric shock, the person may be thrown away from   the circuit.    Source: W.B. Kouwenhoven, "Human Safety and Electric Shock," Electrical   Safety Practices, Monograph, 112, Instrument Society of America, p. 93.   (Papers delivered at the third presentation of the Electrical Safety Course   given in Wilmington, DE, in November 1968.)

Burns and Other Injuries

The most common   shock-related injury is a burn. burns suffered in electrical accidents may be   of three types: electrical burns, arc burns, and thermal contact burns.

Electrical burns are   the result of the electric current flowing through tissues or bone. Tissue   damage is caused by the heat generated by the current flow through the body.   Electrical burns are one of the most serious injuries you can receive and   should be given immediate attention.

Arc or flash burns, on   the other hand, are the result of high temperatures near the body and are   produced by an electric arc or explosion. They should also be attended to promptly.

Finally, thermal   contact burns are those normally experienced when the skin comes in contact   with hot surfaces of overheated electric conductors, conduits, or other   energized equipment. Additionally, clothing may be ignited in an electrical   accident and a thermal burn will result. All three types of burns may be   produced simultaneously.

Electric shock can also   cause injuries of an indirect or secondary nature in which involuntary muscle   reaction from the electric shock can cause bruises, bone fractures, and even   death resulting from collisions or falls. In some cases, injuries caused by   electric shock can be a contributory cause of delayed fatalities.

In addition to shock   and burn hazards, electricity poses other dangers. For example, when a short   circuit occurs, hazards are created from the resulting arcs. If high current   is involved, these arcs can cause injury or start a fire. Extremely   high-energy arcs can damage equipment, causing fragmented metal to fly in all   directions. Even low-energy arcs can cause violent explosions in atmospheres   that contain flammable gases, vapors, or combustible dusts.

Preventing Electrical Hazards

Electrical accidents   appear to be caused by a combination of three possible factors- unsafe   equipment and/or installation, workplaces made unsafe by the environment, and   unsafe work practices. There are various ways of protecting people from the   hazards caused by electricity. These include: insulation, guarding,   grounding, electrical protective devices, and safe work practices.

Insulation

One way to safeguard   individuals from electrically energized wires and parts is through   insulation. An insulator is any material with high resistance to electric   current.

Insulators-such as   glass, mica, rubber, and plastic-are put on conductors to prevent shock,   fires, and short circuits. Before employees prepare to work with electric   equipment, it is always a good idea for them to check the insulation before   making a connection to a power source to be sure there are no exposed wires. The   insulation of flexible cords, such as extension cords, is particularly   vulnerable to damage.

The insulation that   covers conductors is regulated by Subpart S of 29 Code of Federal   Regulations (CFR) Part 1910.302, Design Safety Standards for Electrical   Systems, as published in the Federal Register on January 16, 1981.

Subpart S generally   requires that circuit conductors (the material through which current flows)   be insulated to prevent people from coming into accidental contact with the   current. Also, the insulation should be suitable for the voltage and existing   conditions, such as temperature, moisture, oil, gasoline, or corrosive fumes.   All these factors must be evaluated before the proper choice of insulation   can be made.

Conductors and cables   are marked by the manufacturer to show the maximum voltage and American Wire   Gage size, the type letter of the insulation, and the manufacturer's name or   trademark. Insulation is often color coded. In general, insulated wires used   as equipment grounding conductors are either continuous green or green with   yellow stripes. The grounded conductors that complete a circuit are generally   covered with continuous white or natural gray-colored insulation. The   ungrounded conductors, or "hot wires," may be any color other than   green, white, or gray. They are often colored black or red.

Guarding

Live parts of electric   equipment operating at 50 volts or more must be guarded against accidental   contact. Guarding of live parts may be accomplished by:

·  location in a   room, vault, or similar enclosure accessible only to qualified persons;

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·  use of   permanent, substantial partitions or screens to exclude unqualified persons;

·  location on a   suitable balcony, gallery, or platform elevated and arranged to exclude unqualified   persons; or

·  elevation of 8   feet (2.44 meters) or more above the floor.

Entrances to rooms and   other guarded locations containing exposed live parts must be marked with   conspicuous warning signs forbidding unqualified persons to enter.

Indoor electric wiring   more than 600 volts and that is open to unqualified persons must be made with   metal-enclosed equipment or enclosed in a vault or area controlled by a lock.   In addition, equipment must be marked with appropriate caution signs.

Grounding

Grounding is another   method of protecting employees from electric shock; however, it is normally a   secondary protective measure. The "ground" refers to a conductive   body, usually the earth, and means a conductive connection, whether   intentional or accidental, by which an electric circuit or equipment is   connected to earth or the ground plane. By "grounding" a tool or   electrical system, a low-resistance path to the earth is intentionally   created. When properly done, this path offers sufficiently low resistance and   has sufficient current carrying capacity to prevent the buildup of voltages   that may result in a personnel hazard. This does not guarantee that no one   will receive a shock, be injured, or be killed. It will, however,   substantially reduce the possibility of such accidents - especially when used   in combination with other safety measures discussed in this booklet.

There are two kinds of   grounds required by Design Safety Standards for Electrical Systems (Subpart   S). One of these is called the "service or system ground." In this   instance, one wire-called "the neutral conductor" or "grounded   conductor" - is grounded. In an ordinary low-voltage circuit, the white   (or gray) wire is grounded at the generator or transformer and again at the   service entrance of the building. This type of ground is primarily designed   to protect machines, tools, and insulation against damage.

To offer enhanced   protection to the workers themselves, an additional ground, called the   "equipment ground," must be furnished by providing another path   from the tool or machine through which the current can flow to the ground.   This additional ground safeguards the electric equipment operator in the   event that a malfunction causes the metal frame of the tool to become   accidentally energized. The resulting heavy surge of current will then   activate the circuit protection devices and open the circuit.

Circuit   Protection Devices

Circuit protection   devices are designed to automatically limit or shut off the flow of   electricity in the event of a ground-fault, overload, or short circuit in the   wiring system. Fuses, circuit breakers, and ground-fault circuit interrupters   are three well-known examples of such devices.

Fuses and   circuit-breakers are over-current devices that are placed in circuits to monitor   the amount of current that the circuit will carry. They automatically open or   break the circuit when the amount of current flow becomes excessive and   therefore unsafe. Fuses are designed to melt when too much current flows   through them. Circuit breakers, on the other hand, are designed to trip open   the circuit by electro-mechanical means.

Fuses and circuit   breakers are intended primarily for the protection of conductors and   equipment. They prevent over-heating of wires and components that might otherwise   create hazards for operators. They also open the circuit under certain   hazardous ground-fault conditions.

The ground-fault   circuit interrupter, or GFCI, is designed to shutoff electric power within as   little as 1/40 of a second. It works by comparing the amount of current going   to electric equipment against the amount of current returning from the   equipment along the circuit conductors. If the current difference exceeds 6   milliamperes, the GFCI interrupts the current quickly enough to prevent electrocution.   The GFCI is used in high-risk areas such as wet locations and construction   sites.

Safe Work   Practices

Employees and others   working with electric equipment need to use safe work practices. These   include: deenergizing electric equipment before inspecting or making repairs,   using electric tools that are in good repair, using good judgment when   working near energized lines, and using appropriate protective equipment.   Electrical safety-related work practice requirements are contained in Subpart   S of 29 CFR Part 1910, in Sections 1910.331-1910.335.

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Training

To ensure that they use   safe work practices, employees must be aware of the electrical hazards to   which they will be exposed. Employees must be trained in safety-related work   practices as well as any other procedures necessary for safety from   electrical hazards.

Deenergizing   Electrical Equipment. The accidental or unexpected sudden starting of electrical   equipment can cause severe injury or death. Before ANY inspections or repairs   are made -- even on the so-called low-voltage circuits-the current must be   turned off at the switch box and the switch padlocked in the OFF position. At   the same time, the switch or controls of the machine or other equipment being   locked out of service must be securely tagged to show which equipment or   circuits are being worked on.

Maintenance employees   should be qualified electricians who have been well instructed in lockout   procedures. No two locks should be alike; each key should fit only one lock,   and only one key should be issued to each maintenance employee. If more than   one employee is repairing a piece of equipment, each should lock out the   switch with his or her own lock and never permit anyone else to remove it.   The maintenance worker should at all times be certain that he or she is not   exposing other employees to danger.

Overhead   Lines

If work is to be   performed near overhead power lines, the lines must be deenergized and   grounded by the owner or operator of the lines, or other protective measures   must be provided before work is started. Protective measures (such as   guarding or insulating the lines) must be designed to prevent employees from   contacting the lines.

Unqualified employees   and mechanical equipment must stay at least 10 feet (3.05 meters) away from   overhead power lines. If the voltage is more than 50,000 volts, the clearance   must be increased by 4 inches (10 centimeters) for each additional 10,000   volts.

When mechanical   equipment is being operated near over-head lines, employees standing on the   ground may not contact the equipment unless it is located so that the   required clearance cannot be violated even at the maximum reach of the   equipment.

Protective Equipment. Employees whose occupations   require them to work directly with electricity must use the personal   protective equipment required for the jobs they perform. This equipment may   consist of rubber insulating gloves, hoods, sleeves, matting, blankets, line   hose, and industrial protective helmets.

Tools. To maximize his or her own   safety, an employee should always use tools that work properly. Tools must be   inspected before use, and those found questionable, removed from service and   properly tagged. Tools and other equipment should be regularly maintained.   Inadequate maintenance can cause equipment to deteriorate, resulting in an   unsafe condition.

Tools that are used by   employees to handle energized conductors must be designed and constructed to   withstand the voltages and stresses to which they are exposed.

Good Judgment. Perhaps the single most   successful defense against electrical accidents is the continuous exercising   of good judgment or common sense. All employees should be thoroughly familiar   with the safety procedures for their particular jobs. When work is performed on   electrical equipment, for example, some basic procedures are:

·  Have the equipment deenergized.

·  Ensure that the equipment remains deenergized by using some type of lockout and tag procedure.

·  Use insulating  protective equipment.

·  Keep a safe distance from energized parts.

Conclusion

The control of  electrical hazards is an important part of every safety and health program.   The measures suggested in this article should be of help in establishing such   a program of control. The responsibility for this program should be delegated   to individuals who have a complete knowledge of electricity, electrical work   practices, and the appropriate OSHA standards for installation and   performance.

Everyone has the right  to work in a safe environment. Through cooperative efforts, employers and  employees can learn to identify and eliminate or control electrical hazards.

Footnote(1)0SHA'S   Construction Standards, 29 CFR 1926, Subpart K-equivalent to those in Subpart-S but contain fewer safety-related work practices-comprise electrical safety   requirements. OSHA'S Maritime Standards, 29 CFR Parts 1915, 1917, 1918, and 1919 contain fewer electrical requirements.

Footnote(2)   Fatal Workplace Injuries in 1995: A Collection of Data and Analysis, Table A- 15. Bureau of   Labor Statistics Report 913. U.S. Department of Labor, Washington, DC.

Footnote(3)   Section 18(b), P.L.   95-596, encourages states to develop and operate under OSHA guidance, job   safety and health plans. An OSHA-approved state plan must have safety and   health requirements a least as effective as those of Federal OSHA and must   adopt, within 6 months of promulgation of federal standards, comparable state   standards.

This informational article is intended to provide a   generic, non-exhaustive overview of a particular standards-related topic.   This publication does not itself alter or determine compliance   responsibilities, which are set forth in OSHA standards themselves and the   Occupational Safety and Health Act. Moreover, because interpretations and   enforcement policy may change over time, for additional guidance on OSHA   compliance requirements, the reader should consult current administrative   interpretations and decisions by the Occupational Safety and Health Review   Commission and the courts.

Material contained   in this publication /article is in the public domain and may be reproduced,   fully or partially, without permission of the Federal Government. Source   credit (OSHA) is requested but not required.

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