Electrical Safety
What is the Ventricular fibrillation current? (current value and what it is)
Ventricular fibrillation: 75-400 mA -Rapid disorganized cardiac rhythm
What is one way to check for a proper ground?
• A voltmeter can be used to verify a proper ground • Test an outlet by inserting one voltmeter probe in the incoming slot (shorter slot) and the other in the ground slot • If the ground is working properly, the measured voltage should be very close to the line voltage (can be measured between the two vertical slots)
Which is more dangerous: AC or DC?
AC is more dangerous than DC.
What is over-current protection (OCP) and why is it used?
- Excessive current in wires can cause power dissipation in heat - Proper wire gauge (diameter) and circuit breaker protection are required by NEC to reduce or mitigate those risks (aka over-current protection)
What are two simple protection methods against electrical shocks?
- Insulating Completely all electric current sources and grounded objects - Keeping all conductive surfaces at human reach, at the same potential
What do isolation transformers do within power distribution plants? (How do they create better protection?)
-Isolation transformers transfer electric power while isolating the device from the power source -Isolation transformers have no conductive connection between the transformer secondary (device side) and the ground
What is Microshock?
All the current applied through, and intracardiac catheter flows through the heart
What can AC current interfere with?
Alternating current (AC) can interfere with the natural electrical pulses of the heart.
How does an electric arc occur?
An electric arc occurs when two conductors having large potential difference are in close proximity.
What is a AFCI? What does it stand for? What does it do?
Arc Fault Circuit Interrupters (AFCI): - Special circuit breakers that detect arcs in electrical circuits - Arcs occurs when there is a significant amount of current flow through a very heated air - AFCI's are required in circuits feeding living rooms, bedrooms, family rooms etc. - They are not necessary in places where GFCIs are required (such as in bathrooms)
What is electric shock caused by?
Electric shock caused by is caused by bodily connection to two points that have different potentials.
What is the main cause of death?
Electrical current passing through the body is the main cause of death.
SUMMARY
• Electric shock is caused by the contact of two points with different electric potential • High-frequency RF radiation can cause cancer. High RF energy can burn biological tissue • Exposure to strong magnetic fields around the high- tension power lines is not safe • All equipment should be electrically connected to a ground • GFCIs are required in areas where electricity is used close to water or dampness • AFCIs are used to prevent arc faults, which result in fire hazards • Explosive material and the spark hazard must be reduced in order to prevent explosions • Proper wire gauge and circuit breakers are also used to prevent fire hazards
What should equipment have to provide protection?
• Protection By Equipment's Design: - Reduction of leakage current in the chassis of equipment - Double insulated equipment - Appropriate grounding - Operation at low voltages - Electrical insulation
What are 4 things that you can do to avoid RF hazards?
• Use of "hands free" device instead of cell phones directly to your head • Store cell phone away from your head whenever possible • Avoid standing near radio antennas or transmitters • Avoid living close to high tension power lines
What is an example of Electric-Safety Codes and Standards?
-NEC (National Electrical Code) also known as NFPA (National Fire Protection Association)
What current value causes burns and physical injury?
Burns and physical injury: 10 A
What could happen to gas cylinders in a lab in the presence of an arc?
Explosive gas cylinders in labs (if they're leaking) can cause blasts and explosions in presence of an arc.
What are some explosive materials/gases?
Explosive materials/gases include (but are not limited to): acetylene, ethyl ether, gasoline, methane, alcohol, propane, acetone, hydrogen, oxygen
Extended exposure to RADAR signals causes various health problems. What are they?
Extended exposure to RADAR signals causes various health problems: - leukemia, head aches, brain tumors, internal bleeding, heart conditions, jaundice
What effect does body weight have on the fibrillation threshold?
Generally, the fibrillation threshold increases with body weight
What is a GFCI? What does it stand for? What does it do?
Ground Fault Circuit Interrupters (GFCI): Provides protect from electrical shock by interrupting the power source when a ground fault current between 4mA and 6mA appears. The ground fault current is detected by comparing the amount of current going from and returning to the power source.
What can High frequency RF radiation cause?
High frequency RF radiation can cause cancer.
What do High-frequency RF signals, above 1017Hz cause?
High-frequency RF signals, above 1017Hz cause DNA and biological tissue damage.
What is the Let-go current? (current value and what it is)
Let-go current: 6 mA. It is the maximal current at which the subject can withdraw voluntarily.
What are some hazards caused by low-frequency radiation?
Low-frequency hazards include small added risk of miscarriage, childhood leukemia, brain cancer and greater incidence of suicide.
What is Macroshock?
Only part of the current flows through the heart during Macroshock.
What kind of thermal effects can High-frequency RF energy cause?
RF energy can cause thermal effects such as heating of tissues and burns.
What is a cause of low frequency radiation? (aka What emits it?)
RF radiation at a low frequency (~60Hz) is emitted by high-tension power lines
What current value causes respiratory paralysis, pain, and fatigue?
Respiratory paralysis, pain, and fatigue: 18-22 mA
What happens to the resistance of skin when it is wet?
Skin has less resistance when it is wet. Other info: - Most of the resistance of the skin is in the outer, horny layer of the epidermis - 15 kΩ - 1 MΩ /cm2 (dry, intact skin) - drops to as low as 1% of the value for wet skin
What is the sustained myocardial contraction current value? (and what happens?)
Sustained myocardial contraction: 1-6 A - Entire heart muscle contracts
Are there any federal regulations on EM radiation? Are there any state regulations on EM radiation?
The US Federal government does not acknowledge electromagnetic radiation as dangerous, hence has not issued any regulations concerning building near power lines. However, some US states limit radiation to 200mG (1Tesla=10,000 Gauss).
The effect of power lines on the safety of people depends on what?
The effect of power lines on the safety of people depends on the voltage and current through the power lines.
Why does the Let-go current value rise with frequency?
The let-go currents rise because the muscles can partially relax during part of each cycle. And at frequencies above several hundred hertz, the let-go currents rise again.
What is the most common electrical cause of an explosion ignition?
The most common electrical cause of an explosion ignition is arcs.
What can a power distribution plant do to have better protection?
The power distribution plant can have an isolated system to have better protection. This is obtained by using isolation transformers for large ground currents.
What is the Threshold of Perception? (current value)
Threshold of perception: 2-10 mA.