Safety
Execution of lab work in a safe manner is even more important than performing accurate electronic measurements and construction of neat circuits. The first step is always to become familiar with the lab itself. You should know where the fire extinguishers and the emergency exits are located. Equally as important is the location of nearest phone to call for help. You should also know all equipments and substances that are used in the lab to take the necessary precautions.
The ever-present hazard in an electronics lab is the electric shock. Most people equate the severity of electric shock with the voltage, i.e., a 1,000-V shock is deadlier than a 100-V shock. This is not true. The real measure of a shock is the amount of current that flows through the body. Table below lists the impact of ac (alternating) current on the body:
| Current | Effect |
| 1-5 mA | Threshold of sensation |
| 5-20 mA | Involuntary muscle contraction ("can't let go") |
| 20-100 mA | Pain, breathing difficulties |
| 100-300 mA | Ventricular fibrilation, possible death |
| >300 mA | Respiratory paralysis, burns, unconsciousness |
The amount of the current flowing through the body during an electric shock depends on the voltage and the resistance between the terminals of the voltage source. This resistance consists of: (1) resistance of the contact point between body and circuit (e.g., a ring or a watch), (2) skin resistance at the point the current flows into the body, (3) internal resistance of body, (4) skin resistance where current flows out of the body (e.g., shoes). Obviously, the larger the resistance, the smaller would be the current. Therefore, in order to minimize the electric shock hazard:
- Always power down the electrical equipment, disconnect the power cord, and wait for a few seconds before touching exposed wires. Remember that circuit breakers are usually set for much larger currents (e.g., household breakers are at 15 A and higher) than the current that kill a person (200-300 mA). Do not assume that because your circuit is powered with 5 V, it is not dangerous. In some circuits, capacitors can be charged to a much higher voltage and give you a nasty surprise. Death by electrocution has been reported at a voltage as low as 42 V (DC).
- Do not wear rings, watches, necklace, and any any other loose metallic objects. Rings and watches are specially dangerous as the skin beneath them is wet by sweat, making the resistance of skin much lower.
- Make sure that your hand are dry. Resistance of wet skin can be as low as 1 kOhm as opposed to dry skin which is about 500 kOhm.
- Make sure that your shoes are dry (specially in rainy days). Do not lean on metallic objects (like legs of the bench tables) as you are providing a very large contact area for the current to flow out of your body to ground.
In case of electric shock, cut the power and/or remove the victim as quickly as possible without endangering yourself. If the power switch is not readily available (remember the lab emergency shut-off power switch near the door), use an insulting material such as dry wood, rope, belt, etc. The resistance of body decreases during a shock so action should not be delayed. Send someone to call for help immediately.
If the victim is unconscious and has stopped breathing, start artificial respiration at once. Do not stop until a medical authority has arrived and taken over. Do not stop even if the victim does not have a pulse.
Additional Lab Safety Rules
- Each group is responsible for the their lab bench. After the lab exercise is over, all equipment should be powered down and all probes, cords, etc. returned to their proper position. Do not cut and drop wires on the lab bench. Lose cut wires have caused many short circuits. Your lab grade will be affected if your bench is not tidy when you leave the lab.
- Always get instruction on how to use the tools and instruments. Use only the tool designed to do the job in hand. One tool that requires special attention is the soldering iron. Careless use can result in painful burns and fire. Always put the hot iron in its holder. Turn the iron one only when you need to use it and turn it off when you are done (even if you may need it in 5 minutes). The short warm-up time is a small price to pay for the prevention of potential fire and burn hazards.
- Do not wear rings, watches, necklace, and any any other loose metallic objects (electric shock hazard). Do not wear lose clothing. They cause all sort on un-intentional accidents (from dropping equipments to being set on fire with a soldering iron).
- No open drinks and/or food is allowed near the Lab benches. Spilled drinks have caused many accident.