Occupational electrocutions continue to be a serious problem throughout the United States. Data obtained from the Bureau of Labor Statistics' Annual Survey indicate that approximately 10% of all occupational fatalities are due to electrocutions.¹

If you are not a qualified electrician you should not be servicing any electrical equipment. If you are a qualified individual, always be aware of your work environment and exercise safe working procedures.

Basic Electrical Safety Guidelines

·         Keep your work area clean and orderly. This reduces the chance of accidents and prevents the accumulation of combustibles as well as flammable materials in the workplace.

·         Never work around a source of electricity when you, your surroundings, your clothing, or your tools are wet.

·         Remove all metal jewelry, rings, and watches before working on electrical equipment.

·         Inspect all tools before use for damaged housing and frayed or damaged power cords.

·         Use insulated hand tools and double insulated power tools.

·         Never remove the 3^rd grounding prong from an electrical cord.

·         Permanently remove frayed or defective extension cords from the workplace.

·         Use Ground Fault Interrupters (GFI’s) when working outside, near wet areas or when using extension cords. GFI’s help to protect you from serious electrical shocks and burns by sensing the amount of current going into the piece of equipment and the amount of current going out. If this current differs by as much as 5 milliamps the GFCI will trip within 1/40 of a second. To learn more about GFI’s click on "When to use GFI’s and how they work".

·         Maintain at least 10 feet clearance while working near overhead power lines.

·         Obey proper lockout/tagout procedures to ensure the safety of everyone.

Lockout/Tag-out

Whenever you must work on electrically powered equipment at CHESS, you must the follow appropriate CHESS LNS Lockout/Tag-out procedures outlined below.  If you  have not been trained in CHESS-specific Lockout/Tag-out procedures, contact the CHESS Operator or Dave Jones to receive training before you attempt to use Lockout/Tag-out tags or work on any electrically powered equipment or device.

If you see a piece of equipment with a red lockout/tag-out tag attached, you may not attempt to start, use, or energize that piece of equipment.

Equipment-specific procedures for CHESS equipment are kept in the procedures notebook (also available from Steve Grayat LNS) on the Operator Desk, along with Lockout tags and locks. You must sign out tags and locks in the log book provided.

Procedures that effect the control of hazardous energy require:

LNS/CHESS Lockout/Tag-out Policy

Click here for Cornell EH&S Self-Inspection Checklist for appropriate Lockout/Tagout Procedures

Dangers and Injuries Associated with Electricity

There are several ways in which personal injury may be caused:

1. Personal Injury

(a) Shock

Electric shock is the effect produced on the body, particularly its nervous system, by electric current passing through it, and its effect depends on current strength (which in turn depends on voltage) the path the current takes through the body, the surface resistance of the skin and several other factors.

A voltage as low as 15V can produce discernible shock effects and 70V has been known to cause death. Generally speaking however, fatalities occur from this cause at the normal domestic and industrial voltage of 240V A.C. and from currents of 25-30 milliamps.

The consequences of electric accidents are first of all related to the type of electric risk to which a person is exposed. In second place, to the physical characteristics of the person involved, and, finally, to the context of the installations and the environment, which can escalate from a simple scare by contractions caused by a brief touch, up to loss of life.

RESULTS OF PHYSICAL CONTACT WITH CURRENT/VOLTAGE

Consequences of Low-Voltage Contacts

Contrary to their name, low voltages in normal service are very risky due to their intensive use in all daily activities, which increases the probability of accidents.

·         The most dangerous Direct Contacts, are those which occur under humid conditions, followed by dry contacts. In both cases, a prolonged contact of more than 3 seconds causes, first of all, ventricular fibrillation and then death by asphyxia and/or cardiac arrest. The blood and lymph liquids and muscular water continue boiling and vaporizing until carbonization occurs.

·         The insertion of a resistance, in the case of Indirect Contacts, usually permits an instinctive evasive reaction by the person involved, causing only sharp contractions and distensions of the striated muscles, giving the impression of having been strongly "thrown", which could cause another type of accident due to the fall.

Consequences of Medium and High Voltage Discharges

Despite the gradients that originate the discharge process, Medium and High Voltages in normal service are statistically a lower risk probability because they are not massively used and involves crossing safety or security barriers. Nevertheless, their consequences, although not always lethal, can be disastrous for the victim.

·         In discharges from an energized conductor, the electric power arc that is formed has a current equivalent to that of a short Grounding-Phase circuit, but it closes at the end of its action time, which permits speedy rescue.

·         In discharges from a charged but out-of-service conductor, the electric arc involves transmission of a large amount of electric power in a brief instant, with a current that diminishes drastically and tends to remain at low intensity. Rescue must be carried out very carefully.

Consequences of Voltages due to a Major Grounding Fault

Accidents by potentials due to the dispersion of soil grounding faults, both in substations and in electric line structures, have a low case history and low probability of occurrence, both due to adequate designs of grounding systems and because they are sometimes distant from the pedestrian traffic in such installations, which are also surrounded by clearance or easement areas. However, accidents by poor control of these potentials are usually lethal due to shock or cardiac arrest for the people and any large animals involved.

http://www.procobreperu.org/ingles/PUB_RED_Elec992.htm#2

Death

The most common cause of death from shock is suffocation and it is highly desirable that persons dealing with electricity should be trained in resuscitation, with practice in both artificial respiration and in cardiac massage.

Minor shocks may not in themselves be serious, but can lead to serious consequences, for example, the muscle contraction which they cause may lead to falls from working platforms or ladders.

 (b) Burns

These are caused by the passage of heavy current through the body or by direct contact with an electrically heated surface. They may also be caused by the intense heat generated by arcing from a short-circuit. All cases of burns require immediate medical attention.

(c) Explosion

Where flammable gases or vapours are present, special care is necessary in the design and selection of electrical equipment. In such areas, all equipment should be fully flameproof.

In some cases it is simpler and more economic to isolate the electrical equipment from the flammable vapours - for example with refrigerators used to store flammable solvents the thermostat should be mounted external to the cabinet so that any sparking which occurs is harmless. DO NOT STORE SOLVENTS IN NON-SPARK PROOF REFRIGERATORS OR FREEZERS.

2. Fires

Fires may be caused by any of the following:

(a) Sparks

A spark arises from a sudden discharge through the air between two conductors, or from one conductor to earth. The current produced is usually small, so that serious fires are unlikely unless explosive gases or vapours are present, or highly flammable material is in contact with the conductor.

(b) Short Circuits

A short circuit is formed when the current finds a path from the outward conductor wire to the return wire other than through the equipment to which it is connected. The current flow may be large because of the low resistance of the leads, and arcing often occurs at the contact between the conductors. Insulation may, therefore, be burned and set fire to adjacent flammable material.

(c) Overloading and Old Wiring

Wiring must not be overloaded, otherwise it will overheat and the insulation will be damaged. This can lead to a short circuit at some point in the length of the conductor, or more likely at connection points.

The insulation of wiring which has been in use for a number of years tends to become brittle, and where alterations or additions are required, the installed cable must always be checked by a competent electrician, and replaced completely if there are indications of failure of the insulation.

3. Safety Measures

(a) Protection

Cables must be of sufficient size to carry the current which can flow through them in both normal and abnormal conditions and must be adequately insulated for reasons of safety and of preventing mechanical damage. Those cables which provide the basic services within a building are normally housed in conduit or troughs: particular care is required where apparatus is wired up from socket outlets, and where no such permanent protection is feasible. Such cable must be sufficiently robust to withstand the wear and tear of laboratory use, and fully waterproof where water supplies may be available within the vicinity of the apparatus. Protection against insulation failure must be provided by either fuse or circuit breaker.

Fuse

This device will open a circuit when a predetermined excess of current flows. It may be the rewirable type, or alternatively, may incorporate a wire embedded in insulating powder within a cartridge case. The cartridge fuse is generally more satisfactory.

Circuit Breaker

This is a form of switch which opens automatically if the circuit it controls is overloaded: it may operate on either a thermal or magnetic principle. It is essential to select the correct rating of fuse or circuit breaker for any particular current.

(b) Earthing

The external metal casing of electrical apparatus, cables and conduit must be earthed as a legal requirement. The reasons for this are:-

(i) to prevent the casing rising to a dangerous voltage if some fault arises, for example, a short-circuit between conductors and casing;

(ii) to conduct any current away by a safe path;

(iii) to ensure that a faulty circuit is automatically disconnected from the supply by drawing sufficient current to blow the fuse or operate the circuit breaker.

New equipment should always be checked to ensure that it is properly earthed before putting it into use.

(d) Obstruction

The circulation space in laboratories and workshops must be kept clear to prevent hazards from tripping.

(e) Small Equipment and Tools

Electrical equipment and tools in laboratories and workshops should be regarded as being in normal industrial use, and every precaution for safe handling must be taken. This category would include:

In all instances the connection of these items of equipment to the mains must be correctly made by a competent person.

If you are connecting a plug, make sure the wires are connected to the correct terminals.

Remove only the required amount of insulation so that no bare conductors are exposed when the connections are made, and remove any "whiskers" which may be present.

In general, permanent apparatus having an incidental use in experimental and research work should be:

i) Fully insulated, with switches and terminals enclosed and protected.

ii) Correctly fused, so that the maximum current required can be supplied by any fault is limited to the minimum possible.

iii) Correctly connected to the supply, the line being fused and switched with the earth pin connected. The switch must be inserted into the line or live lead.

iv) Inspected and tested at regular intervals of about a year for earth continuity and general condition.

v) Provided with isolating switches, fuses or plugs, so that they may be removed before the equipment is dismantled.

iv) Not overloaded, a proper consideration of the load magnitude should be made before the apparatus is connected to the supply.

Do not take chances, if in doubt seek assistance and advice.

Reference: http://www.cryst.bbk.ac.uk/~ubcg17a/safety/jim006.html

Case Studies 1:

1. A worker was changing the bulb in a light fixture that had been incorrectly wired (polarity was reversed). He inadvertently touched the metal base of the bulb while it was in contact with the socket. He received a severe shock and later died in hospital.

http://www.csao.org/news/magazine/archives/Spring2000/shock.htm

2. On July 29, 1985, a 29-year-old welder was electrocuted when he inserted the "male" end of an electrical plug on a portable arc welder into a broken "female" connector of an extension cord. As in the previous case, the victim inserted the ground prong of the welder cord 90 degrees clockwise away from the appropriate ground terminal of the extension cord, and the metal casing of the welder connector became energized. It appeared that the connector on the extension cord had been damaged by everyday use or abuse (being thrown down on and dragged across concrete floors, being run over by industrial equipment, etc.)²

Conclusions:

Caution should be used around ALL electrical circuits and equipment. The potential for electric shock should never be underestimated. Employers and other groups should regularly emphasize the safe use of electricity in the workplace. Continuous efforts must be made to prevent electrical injuries and deaths due to damaged receptacles and connectors.

Case Studies 2:

Case #1--SUCCESSFUL RESUSCITATION

A 30-year-old construction worker was working on a fire escape in a building being renovated. Another worker handed the victim a metal pipe, and he was holding it with both hands when it contacted a nearby high voltage line, completing a path-to-ground. The worker instantly collapsed from this contact with electrical energy. Approximately 4 minutes after he collapsed, the fire department rescue squad arrived and began CPR. Within 6 minutes, a paramedic unit was on the scene providing defibrillation and other ACLS measures. They were able to establish a heartbeat and pulse, but the individual continued to require respiratory support during transport to the hospital. He regained consciousness and was discharged within two weeks. He did have to return for further medical care for burns he received on his hands (current entrance) and buttocks (current exit) [6].

Case #2--UNSUCCESSFUL RESUSCITATION

An 18-year-old male restaurant worker contacted electrical energy when he kneeled to plug a portable electric toaster into a 100-120 V/20 amp floor outlet. After a scream was heard, the victim was found convulsing on the damp floor, with one hand on the plug and the other on the receptacle box. The assistant manager went to the electrical panel, but was unable to locate the appropriate circuit breaker. A coworker attempting to take the victim's pulse received an electrical shock, but was not injured. After telephoning the emergency medical service, the assistant manager returned to the panel and de-energized all of the circuits (3 to 8 minutes after the worker contacted electrical energy). The injured worker was covered with a coat to "keep him warm." After about 5 minutes, another call was placed to the emergency squad, and the assistant manager "yelled" for an off-duty employee who lived in an apartment across the lot, who came and began CPR. The emergency service was on the scene 10 minutes after receiving the first call. ACLS measures were available but the resuscitation was unsuccessful and the worker was pronounced "dead on arrival" at the local hospital. The exact time span between the worker contacting electrical energy and the beginning of CPR is unknown, but it is reasonable to assume that it was longer than 4 to 6 minutes. Paramedics with ACLS capability arrived 10 minutes after receiving the call, but more than 10 minutes after the accident occurred [7].

CONCLUSIONS

In Case #1, basic life support was begun within 4 minutes by the fire department rescue squad who happened to be stationed nearby. They were experienced and had up-to-date knowledge in CPR techniques. In this case, CPR was begun within the 4-minute recommendation. An ambulance, equipped and staffed to provide ACLS, arrived within 6 minutes. The standards and guidelines [5] for CPR within 4 minutes, and ACLS within 8 minutes, were met and the worker did survive.

In Case #2, the worker's contact with electrical energy was prolonged and a coworker who aided him received an electrical shock, because coworkers did not know how to de-energize the circuit. The optimal times for CPR and ACLS were exceeded, and the resuscitation was unsuccessful. Providing appropriate medical care after an electrical energy incident will not guarantee success. However, it has been reported elsewhere [5] and supported in the NIOSH case reports, the chance for successful resuscitation after cardiopulmonary arrest is best when the criteria for providing emergency medical care are met.

Niosh Recommendations for Electrical Safety in the Workplace

NIOSH makes the following recommendations in these areas:

1. PROPER UTILIZATION OF ELECTRICAL SYSTEMS

All receptacles and connectors should be used only in accordance with the manufacturers' specifications, and the specific listing for the item as set forth by nationally recognized testing laboratories. Users should be advised of the importance of using receptacles and connectors only for applications for which they have been designed. When a component is selected for use, it should be evaluated to determine if it can tolerate the environment to which it will be exposed. Physical abuse and stress on these components should be minimized by the selection of a safe location and by the use of stress/strain relief devices.

2. AWARENESS AND RECOGNITION OF HAZARDS

Policies that address the proper use of receptacles and connectors should be developed and implemented by qualified safety personnel. Safety training should emphasize awareness and recognition of electrical hazards associated with receptacles and connectors (i.e., broken receptacles and connectors, improper electrical connections, damaged cords, the importance of grounding, etc.). Immediate corrective action should be taken when damaged components or safety hazards are encountered. When safety policies and procedures are developed, they should be enforced.

3. PERIODIC INSPECTION AND MAINTENANCE OF ELECTRICAL SYSTEMS

Periodic inspections should be conducted for all electrical system equipment and components in order to identify all electrical hazards present. Records should be kept of any electrical hazards identified, and appropriate corrective action should be taken immediately. These periodic inspections should be supplemented with daily inspections by the personnel using this equipment.

Citations:

1. NIOSH Electrical Safety Pages

2. Cornell University Lockout/Tag-out Procedures

ADDITIONAL RESOURCES