nd in a confined space. However, they can be even more confined space\" is a con
ID: 2079125 • Letter: N
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nd in a confined space. However, they can be even more confined space" is a confined space that has specific health ardous in a confined space than in a regular worksite and safety hazards associated with it. Permit-required con zards in confined spaces can include poor air quality, fined spaces require assessment of procedures in compli e hazard, noise, moving parts of equipment, temperature ance with Occupational Safety and Health Administration tremes, poor visibility, and barrier failure resulting in a (OSHA) standards prior to entry PART 1 Review Questions Define each of the following terms associated with or 1. Does the severity of an electric shock increase an arc flash decrease with each of the following changes Bolted fault a. A decrease in the source voltage An increase in body current flo Arcing fault Arc blast c. An increase in body resistance d. A decrease in the length of time of exposure Explain why an arc flash is so potential dangerous. 2. a. Calculate the theoretical body current flow (in amperes and milliamperes) of an electric shock State the piece of electrical safety equipment that victim who comes in contact with a 120 V energy should be used to perform each of the following tasks source. Assume a total resistance of 15,000 n a. A switching operation where there is a risk of injury to the eyes or face from an electric arc (skin, body, and ground contacts). b. Using a multimeter to verify the line voltage on a 3-phase 480 volt system b. What effect, if any, would this amount of current likely have on the body? c. opening a manually operated high-voltage dis connect switch. 3. Normally a 6 volt lantern battery capable of deliver- ing 2 A of current is considered safe to handle. Why? 9. outline the safety procedure to follow when you are 4. Why is AC of a 60 Hz frequency considered to be 0. connecting shorting probes across deenergized circuits. List three pieces of personal protection equipment required to be worn most potentially more dangerous than DC of the same voltage and current value? 5. What circuit fault can result in an arc flash? lllllllllllllllllllllllllluu,,,,Explanation / Answer
The severity of electric shock is dependent on the electric current that passes through the body, which inturn is dependent on the voltage and resistance of the path it takes through the body.
1.
a. When the source voltage decreases, the current flowing through the body also decreases as the resistance of the body remains the same. Thus the severity of the shock decreases.
b. An increase in the body current flow, increases the severity of the shock since the current in the body has increased.
c. An increase in body resistance reduces the current flowing through the body for the same source voltage. Hence the severity of shock reduces.
d. The severity of shock is dependent on the duration for which the high current flows through the body. Thus decrease in length of time of exposure, reduces the severity of shock.
2.
a. Current flow = Voltage / Body resistance = 120V/15000 ohms = 0.008Amps = 8mA
b. A current in the range of 10-20mA for 1 second contact would cause an onset of sustained muscular contraction. Since 8mA is very close to this range, the muscular contraction will start when exposed to this range of current for 1 second.
3. A 6V lantern battery capable of delivering 2A of current is considered safe since the voltage is too low to overcome the body’s surface resistance and to drive enough current into the body to be dangerous. For the current to pass through, a large surface area, good conductivity and skin penetration are needed which are very unlikely with this kind of lantern batteries.
4. An AC of 60Hz is considered more dangerous than a DC of the same voltage and current due to the following:
a. Although AC is said to be 120V, it is the RMS value that is specified and not the peak voltage. The peak voltage will be higher than 120V.
b. AC can get into our body more easily than DC. Since the voltage alternates in AC and since our body has capacitance, our body can easily transfer this AC to ground resulting in shock.
c. Also,the alternating nature of AC has the tendency to take the heart to a condition of fibrillation, which is difficult to recover from.
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