Lab Safety Quiz

When must safety glasses be worn?

When soldering, using power tools such as drills

What happens after you have finished soldering and why?

Students should wash their hands with soap and water to remove any residual lead

Are prescription eyeglasses sufficient?

No, they do not offer sufficient protection

Where do you get safety glasses?

Students are responsible for purchasing them and bringing them to each lab class where they will be needed

What happens if you don’t follow the safety standards? If you flagrantly don’t follow them?

Violation of safety standards will not be tolerated. Minor infractions may only incur a verbal warning, but continued failure to follow safe practices may result in removal from the laboratory.

Immediate removal from the lab.

What is forbidden from the laboratory?

Smoking, eating, drinking, and horseplay

What causes many accidents? How should you behave instead?

Haste and inattention. You should work deliberately and carefully, plan your activities prior to the laboratory, familiarize yourself with equipment prior to actual operation, and verify your work as you progress.

What should you learn the location of?

Power switches and ground fault interrupters

Does anything need to be reported?

Report potential hazards and suspected faulty equipment to the instructor immediately. Do not attempt to perform any diagnosis, maintenance, or repairs yourself.

What could happen if you remove or open the case from any apparatus?

It may expose parts at line voltage

Minimize what? What is your last step? What is your first step?

Exposure to live circuits. When wiring a circuit, connecting the source of power. Disconnecting from the power source when disassembling a circuit.

What should you do when adjusting energized circuits?

Exercise caution. All powered circuits are dangerous

How to behave safely and cautiously with circuits?

Use only one hand as far as practical, keeping the other hand disengaged from the circuitry. Do not permit any part of your body to complete a circuit.

Understand handling dangers. Keep watches, rings, and other metallic objects out of contact with live parts. Wet, sweaty, or bleeding hands increase shock hazard.

Watch for exposed wires and other potential shock hazards

What should you do when closing switches?

Close switches quickly and positively. Do not reach for switch handles with your head turned away.

Don’t use what?

Damaged or misapplied parts. Wires that have poor insulation, setscrews that are loose, and insecure connections that may come apart are hazards. Safety devices, coverings, interlocks, etc. must be operational at all times.

Don’t use tools or instruments for other than their original purpose.

What are the three main rules?

Follow procedures, minimize hazards, and avoid unsafe behavior.

What are the three ways electric current damages the body?

1) It harms or interferes with proper functioning of the nervous system and heart

2) It subjects the body to intense heat

3) It causes the muscles to contract

What is the worst case scenario of electric shock?

It can be lethal. The hazards must be understood and general safety rules must be followed.

What kills?

Current. Voltage is not a reliable indication of danger because the body’s resistance varies so widely it is impossible to predict how much current will result from a given voltage.

What current range is especially dangerous?

100-200 mA. It is particularly dangerous because it is almost certain to result in lethal ventricular fibrillation.

Do Victims of high voltage or low voltage shock respond better to artificial respiration?

Victims of high voltage shock. Probably because the higher current clamps the heart and hence prevents fibrillation.

Which is more dangerous? AC or DC? 60Hz current or high frequency current?

AC is more dangerous than DC, 60Hz is more dangerous than high frequency current.

When does skin resistance decrease?

When the skin is wet or when the skin area is in contact with a voltage source increases. It also decreases rapidly with continued exposure to electric current.

What does prevention of electric shock require?

Having a healthy respect for all voltage sources and always following safety procedures when working on electrical equipment. Minimize exposure to live circuits and do not permit any part of your body to complete a circuit.

What happens if someone does suffer a severe shock?

It is important to free the victim from the current as quickly as can be done safely. Do not touch the person until the electric power is turned off. You cannot help by becoming a second victim. The victim should be attended to immediately by a person trained in CPR and an ambulance should be called immediately.

What does the amount of shock-current vary based off of?

It depends on the body’s resistance between the points of contact. A very small current can produce a lethal electric shock (any current over 10 mA).

What happens at each current level?

Shock is more severe as the current rises. At values as low as 20 mA, breathing becomes labored, at values below 75 mA, breathing may cease completely, as current approaches 100 mA, ventricular fibrillation of the heart occurs (an uncoordinated twitching of the walls of the heart’s ventricles). Above 200 mA, the muscular contractions are so severe that the heart is forcibly clamped during the shock which improves survival, yet there will then be other effects.

AC is how much more dangerous than DC?

4 to 5 times more dangerous. AC causes severe muscular contractions and it can lower skin resistance and thereby increase shock-current.

What’s wrong with the standard electrical power frequency?

At 60 Hz, it is in the most harmful range. At this frequency, as little as 25 V can kill. (On the other hand, people have withstood 40,000 volts at a frequency of a million Hertz or so without fatal effects.)

What does the damage?

Current. The resistance of the human body varies so it is impossible to state that one voltage is dangerous and another is safe.

What are some good safety habits?

Using only one hand and standing or sitting on an insulating material. The path through the body has much to do with the shock danger. (A current passing from finger to elbow through the arm may produce only a painful shock, but the same current passing from hand to hand or from hand to foot may well be fatal.) The condition of the skin at the points of contact are critical.

Common protection technologies include what?

Isolation and grounding

Circuit breakers and fuses do not provide what?

Reliable protection upon failure of isolation and grounding. Circuit breakers and fuses are sized to protect equipment and conductors from excessive line currents. They will not protect you.

In some situations it is possible to what?

Isolate energized equipment so that the operator does not come in contact with it. Sometimes equipment is "double insulated," meaning that the operator is separated from current-carrying parts by a double system of insulation. Many handheld power tools are constructed in this manner. Such devices may still present a shock hazard if they are subjected to abuse which damages the insulating materials.

What is the most common method of protecting against electrical shock?

Grounding. All exposed non-current-carrying metal parts of electrical equipment should be grounded. This includes the cases for meters, power supplies, oscilloscopes, etc. used in the laboratory. The case is connected by a grounding conductor to the third prong of a grounding plug which (when inserted into a grounding receptacle) is connected to the building's grounding system..

Proper equipment grounding does what?

It will eliminate high voltages between the equipment and other grounded conducting surfaces. Also, if an energized conductor does touch the grounded case (due to insulation failure, for example) the resulting large current through a low impedance ground path will open the branch circuit fuse or circuit breaker. Without the grounding conductor, the case could be raised to line voltage and the current path to ground might be through the next person to touch it, resulting in a lethal shock.

What is a GFI?

Ground Fault Interrupter. It is a device designed specifically to protect against lethal currents from line-to-ground shocks. The device is generally installed at the electrical receptacle. Various trip settings are available in the range of 5-20 mA. It may be easily reset. The most common type utilizes a differential transformer to detect small differences between line and neutral currents. Most of the receptacles in our laboratories do not have a GFI.