Safety Precautions PDF

# SAFETY PRECAUTIONS 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 injur...

# SAFETY PRECAUTIONS 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. ## 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. ## 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. ## FIRE SAFETY There are three categories of fire, with each requiring special extinguishing techniques. | **Class** | **Combustible materials** | |---|---| | **A** | Combustible materials such as wood, paper, or cloth. Extinguish this type of fire by cooling it with water or smothering it with a $CO_2$ (carbon dioxide) extinguisher. | | **B** | Flammable liquids such as gasoline, kerosene, greases, or solvents. Extinguish by smothering with foam or $CO_2$ extinguisher. | | **C** | Electrical equipment. Extinguish by removing power source and use nonconducting dry power or $CO_2$ 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: | **Amperes (mA)** | **Result** | |---|---| | 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. ## FIRST AID With 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 CPR (cardiopulmonary resuscitation) if necessary. ## 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/](http://www.ilpi.com/msds/) and [http://www.msdssearch.com](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. ## 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. ## SOLDERING When soldering, always observe the following precautions: 1. Always assume the soldering iron is hot. Never touch the tip to see if it is hot. 2. Always place the soldering iron in its holder when idling. 3. Never shake excess solder off the tip; wipe it on a damp sponge or approved tip cleaner. 4. Never pass a soldering iron to another person; place it in the holder and let the other person take it from there. 5. Never solder on a circuit that has power applied to it. 6. Always use a grounded-tip soldering iron. ## STANDARDS 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 if a product meets the minimum safety standards. When purchasing a product, check to determine if it has the UL label on it. The UL label has nothing to do with the quality of a product, only its safety. The Canadian Standard Association (CSA) is similar to the UL safety test. It also has very strict safety codes. The CSA label appears on all types of products, including electrical products. CSA also does on-site inspections of manufacturers on a frequent basis. If a device has both the UL and CSA labels on it, it can be assumed that the device is safe. 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 NEC guidebook helps to minimize electrical fires and to provide safety when doing electrical wiring.