There are many safety hazards to be found in the electrical shop or in the field. The most obvious are electrical hazards and all the things you can see and hear. Other hazards that must be considered may be confined spaces, oil and other fire hazards, and compressed gas and air systems.
A common phenomenon of high-voltage electricity is electrostatic coupling. This is the static voltage or charge impressed upon nearby equipment by an energized high voltage line or bus. The electrical field that is created by current in one conductor can induce voltages into nearby, otherwise de-energized conductors. '''Figure 1''' illustrates this coupling.
'''Figure 1: Electrostatic Coupling'''
This can have several effects. First, the coupling that occurs in the isolated cable is a path for current. Second, it can build a charge because of the capacitive effect and discharge when contacted by a technician. Although this in itself is rarely of sufficient capacity to harm the individual, it can startle you and cause you to make contact with another circuit that is energized from a live source. Again, the use of temporary grounds eliminates this effect.
Capacitors are far too often overlooked as a source of voltage when checking circuits de-energized. Since capacitors store energy, voltage may still be present even after the circuit has been de-energized. When preparing to service a circuit that contains capacitors, it should be done in the following sequence:
Electrical arcs are an extremely dangerous hazard. Too many times, personnel injury has occurred from exposure to an arc that should not have happened and was not expected. This occurrence should always be prepared for by use of the correct protective clothing and eye protection. Severe burns and permanent eye damage can be avoided by simply using protective clothing and eye protection.
Besides the hazards of burns from being near arcs, many injuries occur from direct contact with overheated electrical equipment. A good method to check electrical equipment for overheating is to use the back of your hand to check surfaces. A thumb rule to remember is - if you can not hold the back of your hand to a surface for more than ten seconds - it is hotter than 150 degrees.
A storage battery is constantly alive electrically and is a source of electrical shock. Care must be taken to avoid contacting the positive and negative terminals. Tools and test equipment should never be laid down on top of batteries because of the danger of extreme short circuit currents.
Smoking should never be permitted in a battery charging room or sub-station control house, since all storage batteries generate hydrogen gas during a charge. Ventilation should always be maintained in these areas to prevent a build of explosive gas concentration. The NEC states that provisions will be made for sufficient diffusion and ventilation of gases from the battery to prevent the accumulation of an explosive mixture.
Always avoid contact with the battery acid (electrolyte). The acid is highly corrosive to any material contacted, and dangerous if ingested. It can also irritate soft tissue, such as the face or eyes. If contact with the eyes occurs, an emergency eyewash facility should be used to flush the acid from the eyes. A good neutralizer to use in washing it away from metals, floors, and the tops of the battery cases is a solution of bicarbonate of soda and water.
In almost all cases of fire in electrical equipment, removing the power from the component circuit will stop the fire. Removing the power is the same as removing the fuel. If an electrical fire continues after removing the power, insulation material or debris in the vicinity are usually burning. In any case, you should always extinguish any other material on fire and then cool the area to prevent a re-ignition of the fire.
The most effective extinguisher for use in an electrical fire is a fire extinguisher rated for a Class C fire. The C02and dry chemical extinguishers are both rated Class C. The biggest advantage of using a C02extinguisher is that it will not severely damage any of the electrical circuits it contacts.
A dry chemical extinguisher is corrosive and if it is not completely and immediately removed from all surfaces, it will damage any metal it contacts.
The use of water should be restricted to an extreme emergency, and then only by trained fire fighters capable of dealing with an out of control fire.
Important safety points to remember about the C02and dry chemical extinguishers:
If a transformer containing PCBs is on fire, leave the area and report the fire. When heated above 175° F, PCBs produce phosgene gas. Phosgene gas is toxic and you should not take any action to try to extinguish it yourself. In addition, you should warn the Fire Department of this when they arrive to fight the fire. This will ensure they are wearing the proper respiratory equipment.
If you find a fire, no matter what the cause, you should '''''immediately''''' report it. Always try to remember the plant's emergency number to report a fire or any accident. This emergency number should be posted close to the telephone, if not directly on it. Other emergency actions you can perform for an electrical fire are:
The obvious need for electrical safety is to prevent personnel from being exposed to electricity in an uncontrolled manner that may result in injury or death. Some other concerns are preventing damage to equipment and maintaining power service stability and continuity, but the most personal view is that of the effects of electrical current and high electrical potentials on the human body.
Most people are aware of the fact that the principal danger from electricity is electrocution, but few people understand just how small an amount of current flow is actually required for serious injury or death to occur. To understand these effects, we must look at the factors that affect the severity of a shock.
When current flows through the human body, the person is subjected to an electrical shock. Electrical shock can range from a slight tingling sensation to a feeling of a severe blow. The amount of current flow through the body and the duration of the current flow affects the body in different ways. Have you ever wondered why you can touch both posts of a 12-volt car battery that can produce an electrical current of several hundred amperes, and not feel any sensation of electrical shock The answer is resistance. Dry skin has a resistance level of 100,000 to 600,000 Ω. Recall from Ohm's law that current flow is calculated by dividing the voltage level by the total resistance. If we divide the battery voltage (12V) by the lower figure of skin resistance (100,000 Ω), we find that the current flow is .00012 amperes. Although there is current flow, it is of such a small value that it is not felt. Figure 2 below shows typical body resistances and the expected current flow through various paths through the human body when the voltage level is 100 volts.
Figure 2: Typical Body Resistances and Current Flows
The best way to prevent an electrical shock is to maintain proper distance between current-carrying conductors and any part of your body. This is not always possible. During routine operations, operators and technicians are often required to operate or work on electrical equipment. Because of the possibility of an electrical shock, special precautions are observed:
Follow proper electrical safety precautions while working on or around potentially energized circuits.
In learning about protective equipment that you should wear, some discussion must be made about personal items that you should not wear and the tools that you should not use.
The following personal items should not be worn when working on or around electrical equipment:
The following tools are prohibited for use around electrical equipment due to their conductive nature and the potential for shock hazard should they contact an energized circuit:
There are acceptable substitutes for each of the prohibited items. Ladders made of wood or fiberglass are non-conductive and approved for use around electrical equipment. Tape measures made of cloth or plastic, and fish tapes made of plastic should be used instead of metal. Plastic or rubber-cased flashlights and work lamps are a safe alternative to the metal-cased lights.
OSHA addresses the use of protective equipment, apparel, and tools in article 1910.335a. This article is divided into two parts: ''Personal Protective Equipment'' and ''General Protective Equipment and Tools.''
The first section, ''Personal Protective Equipment'', proposes the following requirements:
The second section, ''General Protective Equipment and Tools'', proposes the requirements listed below:
Electrical safety gloves should always be worn while working on or around energized equipment. It is always safer to de-energize the equipment before performing any work; however, that is not always possible. It may be necessary, while troubleshooting, to check for proper voltages and current levels.
Electrical safety gloves are designed to insulate the user from electrical shock. To guarantee that the user will not receive a shock, the gloves must not only meet stringent manufacturer specifications, but must be properly maintained and inspected prior to each use.
The following terms are frequently used when discussing electrical safety gloves:
'''Figure 3: Rubber Insulating Glove Working Area'''
There are several glove classifications. Each classification is for a specified voltage range. The higher the voltage rating, the thicker the insulation, and the more difficult the gloves will be to use. Class 0 meets all shipboard electrical work voltage rating. See Table below.
'''Proof-Test/Use Voltage Relationship'''
Prior to use, inspect the rubber gloves for defects by stretching a small area at a time (see figure below). Defects include:
Inspect for signs of deterioration caused by:
Additional defects may be identified by inflating the glove with air as follows ('''Figure 4'''):
'''Figure 4: Glove Inspection'''
Leather protector gloves are worn to prevent cutting the rubber glove. Like any work glove they may get dirty or worn. The following guidelines are for leather protectors:
Insulating blankets ('''Figure 5''') are used to insulate a work area to allow work to be performed on energized equipment. They are subject to the same rigorous manufacturing specifications and also require inspection prior to use.
'''Figure 5: Insulating Blanket'''
The most important piece of safety equipment in a performing work in an electrical environment is common sense. All areas of electrical safety precautions and practices draw upon common sense and attention to detail. One of the most dangerous conditions in an electrical work area is a poor attitude toward safety. As stated in article 1910.333a:
'''''Safety-related work practices shall be employed to prevent electric shock or other injuries resulting from either direct or indirect electrical contacts, when work is performed near or on equipment or circuits that are or may be energized. The specific safety related work practices shall be consistent with the nature and extent of the associated electrical hazards.'''''
The following are considered some basic and necessary attitudes and electrical safety precautions that lay the groundwork for a proper safety program. Before going on any electrical work assignment, the following safety precautions should be reviewed and adhered to:
'''All work on electrical equipment should be done with circuits de-energized and cleared or grounded.'''
Obviously, working on energized equipment is much more dangerous than working on equipment that is de energized. Work on energized electrical equipment should be avoided if possible. OSHA 1910.333a.1 states that:
'''''Live parts to which an employee may be exposed shall be de energized before the employee works on or near them, unless the employer can demonstrate that de-energizing introduces additional or increased hazards or is infeasible due to equipment design or operational limitations.'''''
'''All conductors, buses, and connections should be considered energized until proven otherwise.'''
As stated in article 333b.l, conductors and parts of electric equipment that have not been locked out or tagged out according to paragraph (b) of this section (1910.333b.2, ''Lockout and tagging'') shall be treated as energized parts, and paragraph (c) of this section (1910c, ''Working on or near energized parts'') applies to work on or near them.
Furthermore, article 1910.333b.2.iv states that equipment can only be considered de energized when several requirements have been met. One of the requirements states that a qualified person shall use test equipment to test the circuit elements and electrical parts of equipment to which employees will be exposed and shall verify that the circuit elements and equipment parts are de energized.
'''Know the work to be done and how to do it.'''
This is a very broad statement. This common sense rule implies that the work should be done by or under direct supervision of a qualified person. Knowing the results of your every action before you act is a major key to being safe.
'''Check out the entire area you will be in beyond the scope of your work.'''
This precaution is another common sense rule that is very important. This type of attitude will help prevent unexpected conditions near your work area.
'''Use safety apparel and rubber gloves.'''
While working in situations where there are potential electrical hazards, OSHA requires that employees be safeguarded from injury by appropriate protective equipment. All protective equipment shall be maintained in a safe, reliable condition. Protective equipment shall be routinely tested and inspected.
'''Always block off your work areas and never leave your work area unattended unless everything is in a secure condition.'''
As mentioned in article 1910.335b, there are three methods of alerting personnel about hazards:
Safety signs, safety symbols, or accident prevention tags shall be used where necessary to warn employees about any electrical hazards that may endanger them.
In conjunction with safety signs, barricades shall be used where it is necessary to prevent or limit employee access to work areas that may expose them to uninsulated energized conductors or circuit parts.
If signs and barricades do not provide sufficient warning and protection from electrical hazards, an attendant shall be stationed to warn and protect employees.
'''Do not perform work on energized circuits/equipment without direct authorization of your supervisor.'''
When work on energized circuits/equipment has been authorized, use complete planning methods and sufficient precautions to ensure personnel safety. This should be automatic if work is on energized equipment since the OSHA requirement previously stated that equipment shall be de energized. The exceptions to that rule should only be exercised with the supervisor's knowledge of the work.
'''Always stay aware of work conditions and equipment status.'''
Inform your supervisor and other workers of any changes. This ensures that everyone involved is aware of the conditions. When the supervisor is informed of a situation, he or she should immediately inform everyone associated with the work that conditions have changed and assess the need for any additional safety requirements.
'''Never directly touch an unconscious fellow worker that may be in contact with an energized circuit.'''
This rule is a good one for obvious reasons. Instead of being a part of the solution to this situation - you could become part of the problem. There are many ways to remove personnel from live circuits without touching them.
'''Do not perform or continue to perform any work when you are in doubt about the safety procedure to be followed, the condition of the equipment, or potential hazards.'''
In applying these precautions and philosophies in performing your work, you should never overlook the use of common sense and attention to detail. Taking your time and assessing situations and conditions prior to beginning an assignment will go far toward eliminating many possible hazards. Additionally, whenever you are performing any task - routine and frequent or difficult and infrequent - always prepare yourself for the unexpected.