Electrical Flashcards
What is injury/death rate for electrical hazards?
*while a fraction of total workplace injuries, likely to result in death
*Electrical hazards cause approximately 4000 injuries per year
*Average of 13 days away from work and nearly one fatality every day
*Over 400 electrocutions in the US a year
What are the main causes of electrocution?
*20% wiring
*9% ladders contacting power lines
*9% power tools
*7% landscaping, gardening, and farming equipment
How does electricty work? (see notes for picture)
a complete circuit is maintained between the tool and the energy source
- if the tool is damaged, the person may come in contact with electricity and can become a path for the current
*The person will be shocked
What is the first electrical hazard?
electrical shock
- when the human body becomes a conductor, completing the path for the current to flow
- Like water, electricity will take the path of least resistance. Current will most likely flow through a circuit instead of a human body, unless the body presents a path of lower resistance.
What are the major causes of eletrical shock?
- exposed electrical parts
- not properly grounded equipment
- Wet or damp surfaces
- Damaged insulation
- Overloaded circuit
- Overhead power lines
What are the rules for exposed electrical parts?
- outer insulation on electrical cord must be intact
- Never use an electrical panel that has exposed wires
- All openings must be closed
What is improper grounding?
- the ground pin safely returns leakage current to ground
- Never remove the ground pin
How do wet conditions effect electrical components?
- water increases the risk of electrical shock
- Always avoid using tools in wet locations
How does damaged insulation effect electrical equipment?
- defective, or inadequate insulation is a hazard
- Never use tools or extension cords with damaged insulation
- Insulation prevents conductors from contacting each other or you
- Never hang extension cords from nails or sharp objects
What are ground faults?
- occurs when current flowing to the load (drill, saw, etc) does not return by the prescribed route
- Current travels through the black (ungrounded) wired to the load and returns to the source through the white (grounded) wire
- a persons body can act as the path to ground when a fault occurs
How do you avoid grounding hazards? (2 steps)
- Electrical circuit or system grounding
* ground all power supply systems, electrical, circuits, and electrical equipment
* do not remove ground pins/prongs from cord
* use double insulated tools - Electrical equipment grounding
* all metal frames and enclosures of equipment are grounded by a permanent connection or bond
* The equipment, grounding conductor provides a path for dangerous fault current to return to the system, ground at the supplies or should occur
What are ground fault circuit interrupters (GFCI’s)
- to send an imbalance and current flow
- at the current flow differs by over 5MA +/- 1MA, the GFCI will quickly open the circuit
- it is not an overcurrent device like a fuse or circuit breaker
What is the second electrical hazard?
Arc flash/arc blast
a phenomenon where a flashover of electric current leaves its intended path and travels through the air from one conductor to another, or to the ground
What is arc flash/blast caused by?
dust, dropping tools, accidental touching, condensation, material failure, corrosion, faulty installation
What are results of arc flash?
burns, fire, flying objects
What is the 3rd electrical hazard?
Burns
result when a person touches electrical wiring or equipment that is energized
What are thermal contact burns?
skin comes in contact with overheated, electrical equipment, or when clothing is ignited in an electrical incident
What are electrical burns?
- causes tissue damage
- Result of heat generated by the flow of electric through the body. Is one of the most serious body injuries you can receive
- High temperature is near the body, produced by an electrical arc or explosion. cause arc flash burns.
What are injuries that can occur from electrical hazards?
Internal
* we small amounts of current and extra current leads to serious damage
* Internal bleeding, tissue destruction, and nerve or muscle damage
* May not be immediately apparent to the victim/observers; however, if left
untreated, they can result in death
Involuntary muscle contraction
* muscle violently contracts when stimulated by excessive electricity
What are the 4th and 5th hazards that can occur from explosions and fires?
Explosions
* explosions occur when electricity provide a source of ignition for an
explosive mixture in the atmosphere
Fires
* electricity is one of the most common causes of fires both both in the
home and in the workplace. Defective or misuse electrical equipment is a
major cause.
How is low-voltage still hazardous?
- the degree of injury increases with the length of time the body is in the circuit
- Even relatively low voltages can be extremely dangerous
- an exposure of 100 mA for three seconds, can cause the same amount of
damage as an exposure of 900 mA for .03 seconds
How does water and conduction work?
- Water influences the conductive properties of some materials
- use extreme caution when working with electricity, where there is water in the environment or on the skin
- Example: Dry wood is a poor conductor and Wood saturated with water becomes a ready conductor. Dry conditions means human skin is resistant
How is two control stage applied to electrical hazards?
- Two stage control (stage one cannot be used)
- Identify the purpose of various engineering controls designed for electrical safety
- The preferred method to control electrical hazards is to engineer controls
into the design of equipment - Engineered safeguards can be as simple as a light switch cover or a door on the breaker panel
What are adminstrative control examples when it comes to electrical hazards?
- warning signs, labels, tags
- Procedures
- Work planning/control documents
- Work related training, and certifications
- Lockout/tag out
When are internal barriers required?
- ground fault circuit interrupters are required under the following conditions
- damp or wet location
- within 6 feet of exterior door
- Outdoors
- Rooftops
What is the control of hazardous energy?
- referred to as the lock-out/tag-out
- The purpose of this regulation is to protect people from hazardous energy while performing service/maintenance on machines, tools, and equipment
- Safeguards against unexpected start up of equipment or process
What are sources of energy?
-Electrical
-Water
-steam
-Pneumatic
-natural gas
-hydraulic
-mechanical
What are the basic steps for a lock-out/tag out?
Step one: detailed procedures for equipment Step two: notify affected employees
Step three: shut down equipment properly
Step four: disconnect all primary energy sources Step five: address all secondary sources
Step six: verify the lockout
Step seven: keep it in force during shift changes
Step eight: bring the equipment back online
What are some points to remember about electrical hazards?
- if you see a lock on equipment, do not attempt to operate
- to gain access to a locked and tagged out circuit contact the person named on the tag
- do not remove the tag or restore without an approval
- electrical locking devices may be installed on a cord, switch, breaker or disconnect device: look before you operate the equipment
- qualified person – NFPA 70E
