After completing this topic, the student will be able to:

• Identify the dangers of working with electricity.

• Understand how to handle a situation when someone is getting shocked.

• Work confidently on electrical circuits and equipment, following guidelines.

• Identify two techniques to prevent electrical shock.

• Understand the purpose of a ground fault circuit interrupter (GFCI).

• Know what labels to look for when using electrical tools and equipment.

• Identify the dangers of static electricity with semiconductor devices.

• List precautions required to minimize electrostatic discharge (ESD).

• Know how to work safely with electricity.

• Understand the purpose of a material safety data sheet (MSDS).

When working with electricity, it is the technician’s responsibility to prevent electrical shock and on-the-job injuries and know how to identify the dangers of working with electricity. Static electricity is an electrical charge at rest on a surface. The static charge becomes larger through the action of contact and separation or by motion. The electrostatic discharge takes place when the charged body comes near or touches a neutral surface.

The following safety precautions are not intended as a replacement for information given in class or lab manuals. If at any time you question what steps or procedures to follow, consult your teacher.

GENERAL SAFETY PRECAUTIONS

Because of the possibility of personal injury, danger of fire, and possible damage to equipment and materials, all work on electrical and electronic circuits should be conducted following these basic safety procedures.

1. Remove power from the circuit or equipment prior to working on it. Never override interlock safety devices. Never assume the circuit is off; check it with a voltmeter.

2. Remove and replace fuses only after the power to the circuit has been deenergized.

3. Make sure all equipment is properly grounded.

4. Use extreme caution when removing or installing batteries containing acid.

5. Use cleaning fluids only in well-ventilated spaces.

6. Dispose of cleaning rags and other flammable materials in tightly closed metal containers.

7. In case of an electrical fire, deenergize the circuit and report it immediately to the appropriate authority.

Work smart and safe when dealing with electricity. You can help protect yourself and everyone around you from painful or even lethal shock. You can also help prevent fires. During the winter months, the skin dries out, offering some insulation. When the skin becomes wet through water or sweat, the body resistance drops. The low resistance allows more current to pass through the body, resulting in impairment.

HIGH VOLTAGE SAFETY PRECAUTIONS

As people become familiar with working on circuits, it is human nature to become careless with routine procedures. Many pieces of electrical equipment use voltages that are dangerous and can be fatal if contacted. The following precautions should be followed at all times when working on or near high-voltage circuits:

1. Consider the result of each act. There is absolutely no reason for individuals to take chances that will endanger their life or the lives of others.

2. Keep away from live circuits. Do not work on or make adjustments with high voltage on.

3. Do not work alone. Always work in the presence of another person capable of providing assistance and first aid in case of an emergency. People who are considering a career working in the electricity and electronics field should become CPR certified.

4. Do not tamper with interlocks.

5. Do not ground yourself. Make sure you are not grounded when making adjustments or using measuring instruments. Use only one hand when connecting equipment to a circuit. Make it a practice to put one hand in your rear pocket.

6. Use an isolation transformer when working on AC-powered circuits/equipment. An isolation transformer isolates the circuit/equipment from the power source, adding an additional safety factor.

7. Never energize equipment in the presence of water leakage.

• Voltage is the pressure behind electrical current, which can result in electrical shock.

• The higher the body resistance, the less current will flow through it.

• When dealing with someone who is experiencing severe electrical shock, send for help; locate and remove the source of power.

• Do not work on any circuit or equipment unless the power is secured.

• Insulating and grounding are two techniques for preventing electrical shock when working with electrical tools and equipment.

• A GFCI is a fast acting circuit breaker that is sensitive to very low levels of current leakage to ground.

• An Underwriters Laboratories label and a Canadian Standards Association label on a product indicate that it is safe to use as intended without any response to its quality.

• When a charged substance discharges through a conductor, an electric current flows to ground potential and is referred to as electrostatic discharge (ESD).

• A person can feel a shock from an electrostatic discharge of 3500 to 4000 volts.

• Components on printed circuit boards can be damaged by static electricity, referred to as electrostatic discharge (ESD).

• Antistatic workstations are designed to provide a ground path for static charges that could damage a component

One technique to reduce current flow is to increase body resistance. Body resistance is high when the skin moisture content is low, and the skin has no cuts or abrasions at the point of electrical contact. In these situations, very little current flows, with a mild shock resulting. If the situation were reversed, with high skin moisture content lowering the body resistance, a large current would flow. If the current flows through the chest region, the heart could go into ventricular fibrillation, resulting in rapid and irregular muscle contractions and leading to cardiac arrest and respiratory failure.

Factors that influence the effects of electrical shock are listed here:

• Intensity of the current

• Frequency of the current

• Current path through the body

• Length of time current passes through the body

Remember, it is the amount of current flow through the body, not the amount of voltage contacted, which determines the severity of a shock. The larger the current flow through the body, the greater the effect of the shock.

When dealing with someone who has experienced severe electrical shock, do not become part of the problem. First, send for help; then remove the source of power. Do not attempt to touch or pull the victim away without removing the power source, or you will also get yourself shocked.

If the power source cannot be secured, use a nonconducting material to remove the victim from the circuit. Once the victim is free, check for signs of breathing and pulse. If trained, begin cardiopulmonary resuscitation (CPR) if necessary. CPR is an emergency procedure performed by trained personnel to manually pump blood to the brain until further action can be taken by a qualified medically trained team to restore blood circulation and breathing for a person in cardiac arrest and respiratory failure.

PERSONAL SAFETY PRECAUTIONS

Take time to be safe when working on electrical and electronic circuits. Do not work on any circuits or equipment unless the power is secured.

1. Work only in clean, dry areas. Avoid working in damp or wet locations because the resistance of the skin will be lower; this increases the chance of electrical shock.

2. Do not wear loose or flapping clothing. Not only may it get caught, but it might also serve as a path for the conduction of electricity.

3. Wear only nonconductive shoes. This will reduce the chance of electrical shock.

4. Remove all rings, wristwatches, bracelets, ID chains and tags, and similar metal items. Avoid clothing that contains exposed metal zippers, buttons, or other types of metal fasteners. The metal can act as a conductor, heat up, and cause a bad burn.

5. Do not use bare hands to remove hot parts.

6. Use a shorting stick to remove high-voltage charges on capacitors. Capacitors can hold a charge for long periods of time and are frequently overlooked.

7. Make certain that the equipment being used is properly grounded with polarized plugs. Ground all test equipment to the circuit and/or equipment under test.

8. Remove power to a circuit prior to connecting alligator clips. Handling uninsulated alligator clips could cause potential shock hazards.

9. When measuring voltages over 300 volts, do not hold the test prods. This eliminates the possibility of shock from leakage on the probes. Safety is everyone’s responsibility. It is the job of everybody in and out of class to exercise proper precautions to ensure that no one will be injured and no equipment will be damaged.

Every class in which you work should emphasize and practice safety.

There are two techniques to prevent electrical shock when using electrical tools and equipment. They are insulating and grounding. Insulating refers to using a material that does not support current flow. Copper wire conductors are normally insulated. Hand and power tools and appliances contain layers of insulating material between the interior parts and the exterior housing. grounding helps to provide a path to carry the current to ground. All appliances are grounded. Three-prong plugs are an efficient way to ground tools or appliances, A ground fault circuit interrupter (gfci) is a fast-acting circuit breaker that is sensitive to very low levels of current leakage to ground. GFCIs are designed to limit electrical shock to prevent serious injury. The disadvantage with GFCIs is that they operate only on line-to-ground fault currents.

Typically, these are currents leaking through insulation or current that flows during an accidental contact with a hot wire.

An underwriters laboratories (ul) label on a device implies that the product bearing the label is safe for use as intended. Tests completed by Underwriters Laboratories determine whether a product meets the minimum safety standards. When purchasing a product, check to determine whether it has the UL label on it. The UL label has nothing to do with the quality of a product, only its safety. A CSA certification mark indicates that a product has been tested and meets the requirements of recognized standards used as a basis for certification.

Only when a product has been certified to an applicable standard does it bear the appropriate CSA certification mark. Certification marks appear on a product’s packaging as well as on, or adhered to, the product itself. For consumers, the mark provides increased assurance of safety.

A CSA Group Mark with the indicators “C” and “US” or “NRTL/C” means that the product is certified for both the U.S. and Canadian markets, to the applicable U.S. and Canadian standards. A canadian standards association (csa) mark with the indicator “US” or “NRTL” means that the product is certified for the U.S. market only to the applicable U.S. standards. A number of insurance companies have formed a group known as the National Fire Protection Association. Every few years, this group publishes a summary of electrical-wiring codes under the general heading of the National Electrical Code (NEC). The purpose of this code is to provide guidelines for safe wiring practices in residential and commercial buildings.

State and local municipalities may require even more stringent codes than the NEC that must be followed. In many states, all wiring must be done or approved by a master electrician. These codes are published for both your own and your neighbor’s protection. Electrical fires can and do happen, and they can spread to adjacent homes or apartments. The rules in the NEC guidebook help to minimize electrical fires and to provide safety in electrical wiring.

The Philippine Standard (PS) Quality and/or Safety Mark and Import Commodity Clearance (ICC) Sticker serve as the consumers' guide and assurance that what they purchase are certified quality and safety products conforming to the relevant Philippine National Standards (PNS).

Safety Practices

Effective safety habits are necessary to succeed in the electronics field. Practicing good safety habits promotes a safe work environment. Everyone needs to be aware of and support a safe work environment. A primary concern in the field of electronics is electrical shock, which is the passage of current through the body. Current can flow through the body just as it does through an electrical circuit. How much current flows depends on these factors:

• Body resistance is high if the skin is dry and there are no cuts or abrasions at the point of electrical contact. This results in little current flow with only a mild shock.

• Body resistance is low if the skin is moist. This results in a high current flow, and if the current flow is through the chest region, the heart can receive a lethal dose of current. The heart may go into fibrillation and breathing may be stopped.

Small amounts of current through the body can be dangerous to one’s health. Large amounts of current through the body can be fatal. A shock of 1 to 20 mA can cause a painful sensation. At a shock of approximately 20 to 30 mA, breathing stops. A shock above 100 mA results in electrocution. The work environment should be reviewed to identify problem areas. Maintaining a safe work environment is easy when you observe the following guidelines:

1. Keep the work area neat and orderly.

2. Be alert and attentive at all times.

3. Know the correct operation and safety procedures of test equipment, tools, and machinery.

4. If an accident occurs, know what action to take.

Personal safety when working with electricity requires the following:

• Work with one hand in your back pocket or behind your back when working on live circuits. This technique avoids a complete path for current flow that passes through the heart region.

• Use an isolation transformer when working on AC-powered equipment. The transformer isolates the powered equipment from the power source.

• Make sure all capacitors are discharged before beginning troubleshooting. Use a capacitor discharge tool to discharge the capacitor.

• Use grounded line cords and polarized plugs with AC-operated equipment and circuits. They help to reduce the danger from hot chassis.

• Keep hands off live circuits. Test all circuits with a voltmeter or test lamp before working on them.

Before handling toxic and hazardous chemicals, read the material safety data sheet (MSDS) to know the best protection and first-aid procedures in case of emergency. When around these types of chemicals, be concerned about inhaling vapors, swallowing liquids, acid burns on the skin, contact with the eyes, and danger of fire and explosions. Follow these guidelines to minimize risk:

• Read the labels of all chemicals being used, paying special attention to the printed warnings.

• Work in well-ventilated areas, especially when working with paint and chemical sprays.

• Wear safety glasses when working with hazardous chemicals.

• Wear rubber gloves when working with acids and acid solutions.

• Use tongs or rubber gloves when placing or removing printed circuit boards from the acid solution.

• Clean all tools that contact hazardous chemicals in case anyone accidentally touches them.

FIRE SAFETY

There are three categories of fire, with each requiring special extinguishing techniques.

Class A

Combustible materials such as wood, paper, or cloth. Extinguish this type of fire by cooling it with water or smothering it with a CO2 (carbon dioxide) extinguisher.

Class B

Flammable liquids such as gasoline, kerosene, greases, or solvents. Extinguish by smothering with foam or CO2 extinguisher.

Class C

Electrical equipment. Extinguish by removing power source and use nonconducting dry power or CO2 extinguisher.

ELECTRICAL SHOCK

A major hazard when working with electricity and electronic circuits is electrical shock. Electrical shock occurs when an electric current flows through the body when a complete circuit exists.

Different levels of current produce the following results:

0.001 Ampere (1 mA) - A mild tingling sensation that can be felt.

0.010 Ampere (10 mA) - Start to lose muscular control.

0.030 Ampere (30 mA) - Breathing becomes upset and labored. Muscular paralysis.

0.100 Ampere (100 mA) - Death if the current lasts for more than a second.

0.200 Ampere (200 mA) Severe burns, breathing stops. Death.

One technique to reduce current flow is to increase body resistance. Body resistance is high when the skin moisture content is low with no cuts or abrasions at the point of electrical contact. In these situations, very little current will flow, with a mild shock resulting.

If the situation were reversed with high skin moisture content, lowering the body resistance, a large current would flow. If the current flows through the chest region, the heart could go into ventricular fibrillation, resulting in rapid and irregular muscle contractions and leading to cardiac arrest and respiratory failure.

The factors that influence the effects of electrical shock include:

• Intensity of the current

• Frequency of the current

• Current path through the body

• Length of time current passes through the body

Remember, it is the amount of current flow through the body, not the amount of voltage contacted, that determines the severity of a shock. The larger the current through the body, the greater the effect of the shock.

BREAKING CONTACT WITH ELECTRICITY

1. Before beginning any treatment, look first, do not touch. If the casualty is still in contact with the electrical source, she will be “live” and you risk electrocution.

2. Turn off the source of electricity, if possible, to break the contact between the casualty and the electrical supply. Switch off the current at the mains or meter point if possible. Otherwise remove the plug or wrench the cable free.

3. Alternatively, move the source away from both you and the casualty. Stand on some dry insulating material, such as a wooden box, plastic mat or telephone directory. Using a wooden pole or broom, push the casualty’s limb away from the electrical source or push the source away from her.

4. If it is not possible to break the contact using a wooden object, loop a length of rope around the casualty’s ankles or under the arms, taking great care not to touch her, and pull her away from the source of the electrical current.

5. Once you are sure that the contact between the casualty and the electricity has been broken, perform a primary survey and treat injuries in order of priority.

HAZARDOUS CHEMICALS

Concerns with hazardous chemicals include breathing vapors, contact with skin and eyes, injecting liquids, and danger of fire or explosions. Chemicals found in the electronics laboratory include adhesives, cleaning solvents, etching solutions, photographic developing solutions, screenprinting developing and cleaning solutions, solder fumes, and spray paints.

Observe the following safety practices when working with chemicals:

1. Always wear safety glasses when working with hazardous chemicals.

2. Wear protective rubber/vinyl gloves when working with acids.

3. Use tongs when handling printed circuits being etched.

4. Read the label on all chemicals being used.

5. Work in a well-ventilated space.

6. Wash all tools that contact any hazardous chemical.

7. Always label containers with chemicals.

8. Do not store chemicals in glass containers if possible.

9. Store all chemicals in a flammable metal storage cabinet.

In case of contact with a hazardous chemical, read the label and follow instructions and send for expert medical help.

Various hazardous materials are used throughout the electronics industry. These materials are clearly identified and classified through the MSDS system. Handling and disposing procedures and information can be obtained from specific manufacturer’s websites or through many online resources, such as http://www.ilpi.com/msds/ and http://www.msdssearch.com

ELECTROSTATIC DISCHARGE (ESD)

Static electricity is an electrical charge at rest on a surface. The static charge becomes larger through the action of contact and separation or by motion. The electrostatic discharge takes place when the charged body comes near or touches a neutral surface.

A surface can become charged through three means. The most common means is an electrical charge generated by friction. Rubbing two dissimilar materials together will generate an electrical charge. Walking across a floor or removing a garment will develop a voltage in excess of 5000 volts. It takes approximately 5000 volts to jump approximately 1/4 of an inch.

Induction is a second means of developing a charge. When a person handles a printed circuit board or electronic component wrapped in a plastic material, they induce a charge into the contents of the plastic wrap. When another person removes the plastic wrap, the sudden discharge results in ESD damage.

Capacitance is the third means of generating a static charge. Capacitance is inversely related to the distance between two surfaces. A low voltage can become harmful as one surface is removed further from the other surface or ground. When a circuit is picked up from a table its relative capacitance decreases and voltage increases. When the circuit is grounded again, damage will occur by the large voltage discharging that was generated when the circuit was originally lifted.

Metal oxide semiconductors (MOSs) are extremely sensitive to static charges, as are CMOSs, FETs, VLSI ICs, NMOSs, PMOSs, Schottky diodes, and ECL and linear ICs devices.

High humidity can increase surface conductivity, which reduces friction-generated static electricity. The increased humidity spreads the charge over a larger surface area, reducing the field intensity, and allows the charge to bleed off to ground.

Manufacturers have designed protective circuitry to help dissipate ESD using zener diodes and limiting resistors. ESD prevention requires the awareness and practice of the following procedures.

1. Treat all electronic components and circuits as static sensitive.

2. Do not touch the leads, pins, or components of printed circuit board traces.

3. Before handling a component or circuit, discharge yourself by touching a grounded metal surface.

4. Keep components in original packing materials until needed.

5. Never slide static components over any surface.

The following list identifies precautions required to minimize electrostatic discharge:

1. Before starting work on sensitive electronic equipment or circuits, the electronics technician should be grounded using a wrist strap to discharge any static electric charge built up on the body.

2. Always check manuals and package materials for ESD warnings and instructions.

3. Always discharge the package of an ESD-sensitive device before removing it. Keep the package grounded until the device is placed in the circuit.

4. Minimize the handling of ESD devices. Handle an ESD device only when ready to place it in the circuit.

5. When handling an ESD device, minimize physical movement such as scuffing feet.

6. When removing and replacing an ESD device, avoid touching the component leads.

7. Do not permit an ESD device to come in contact with clothing or other ungrounded materials that could have an electrostatic discharge.

8. Before touching an ESD device, always touch the surface on which it rests for a minimum of 1 second to provide a discharge path.

9. When working on a circuit containing an ESD device, do not touch any material that will create a static charge.

10. Use a soldering iron with the tip grounded. Do not use plastic solder suckers with ESD devices.

11. Ground the leads of test equipment momentarily before energizing the test equipment and before probing an ESD device.

HAND TOOLS

When using hand tools, always observe the following precautions:

1. Always use the proper tool for the job. Use the right type and size tool for each application.

2. When carrying tools, always keep the cutting edge down.

3. Keep hands clean when using tools. Avoid grease, dirt, or oil on hands when using any tool.

4. Clamp small pieces when using a hacksaw, screwdriver, or soldering iron.

5. Avoid using chisels and punches with mushroomed heads.

6. Never use a file without a handle.

7. Never use plastic-handled tools near an open flame.

8. Keep metal rules clear of electrical circuits.

9. Disconnect all electrical devices by pulling directly on the plug, never the cord.

10. When cutting wire, always cut one wire at a time to avoid damaging the cutting tool.

POWER TOOLS

When using power tools, always observe the following precautions:

1. Only the operator starts or stops a machine. When stopping a machine, wait until it comes to a complete stop before leaving the machine.

2. Make all adjustments to the machine prior to turning it on.

3. Never have any loose hand tools, rags, or brushes in the work area when applying power.

4. Keep all safety guards in their proper position at all times.

5. Never force a cutting or drilling tool into a workpiece.

6. Only one person in the work zone at all times power is applied.

7. Have instructor check any special setups prior to applying power.

8. Use only grounded power tools with three prong plugs or UL (Underwriters Laboratories)

-approved housing power tools.