In the United States, enforcement of safety work rules resides with the
Occupational; Safety and Health Administration OSHA
A worker neglecting to wear cut resistant chaps while operating a chainsaw is committing an unsafe ____, while an employee failing to provide is creating an unsafe _____
Act, condition
The ______ - ________ rule suggested that workers should take time before starting a job to check for potentially unsafe conditions and confer about them.
Two - minute
According to ANSI Z133, the minimum approach distance for persons other than qualified line-clearance arborists for 7.2 kV is ____ feet / ___ m.
10 feet
3.05 meter
Surface temperatures at the point of contact with high voltage can reach ____C /. _____’ F
1000, 1832
____ _____ occurs when someone touches an energized fixture. ___ ___ can occur when a person touches a conductive object that is in contact with an energized fixture.
Direct
Indirect
The difference in voltage between 2 objects someone simultaneously contacts is termed ___ ____.
Touch potential
____ _____ is the difference in voltage on the ground between 2 of a persons body parts near where electricity goes into they ground.
Step potential
An energized human body, tree, or climbing rope are all examples of ___ ____ threats.
Indirect contact
The safety acronym S.T.A.R stands for
Stop
Think
Act
Review
T/F - There are no published safety data related specifically to utility arboriculture.
T
Why is over reliance on discipline counterproductive to a safety program?
“Bad things happen to bad people” discourages employees to come forward.
Why should arborists be aware of back feed, and under what circumstances does it occur?
Back feed is electrical flow in an unintended direction through a transformer. Home generators can cause this.
Kinetic energy is dependent on ____ and ____
Mass and velocity
Kinetic energy formula
KE = (weight / 2) x speed squared
With kinetic energy doubling the weight ____ the energy and doubling the speed _____ the energy
Doubles
Quadruples
The death threshold where even small objects can kill
40ft, 12m
Anyone struck by branch falling more than _____or someone fallen more than _____ ft might be suffering from serious injury.
A few feet
15ft or 5m
Passage of electrical current through human body
Electrical shock
Death from electrical shock is
Electrocution
Contact with only _____ can disrupt a persons nervous system to the point they can’t release their grasp.
_____ can cause respiratory paralysis.
_____ can trigger ventricular fibrillation leading to death
____ can cause cardiac arrest and internal organ damage
____ will kill upright
16 milliamps
20 milliamps
100 milliamps
2 amps
15 to 20 amps
Someone contacting high voltage l can create a fault current the build to. _______
Thousands of amps
Human skin is a ___ conductor
Poor
Bones are ____ to electrical conduction
Resistant
ANSI Z133 defines electrical hazard as existing any time a worker, tool, tree, or other conductive object is closer than ___ ft form energized overhead conductor rated ___ kV or less
American standard for aboriculture operations
10
50
Qualified vs incidental line clearance
Qualified - done on behalf of utility
Incidental - work not being done for utility. MAD is slightly more. Lines must be de energized.
Tree on line: in order to avoid the risk of step potential, stay at least. _____ away from base of tree, tree part, or other potentially energized object on the ground.
35 ft
Surprising to many, is that if the electrified worker is not immediately electrocuted by the contact, they often survive to be rescued ___ to ___ minutes later after line has been de energized
20 to 40
Protective grounds
Provide defense against inadvertent re-energization, which can result from back feed, contact with neighboring circuits, or lightning.
During re - energization, grounds cause a. __________, directing the current to ________
Short circuit
Ground
Lines should not be considered de-energized unless
Visible grounds are present.
For intact lines, _____ of grounds is considered sufficient for most utilities
Single. Set
Single point grounding -
Setting grounds between the conductors, the system neutral, (on wye configuration), and the ground (a tower or pole ground) that establishes a equipotential zone.
Equipotential zone -
A work area at a near identical state of electrical potential and is safe to work.
When lines are downed how should grounds be placed?
A set of grounds on either side of the break
Bracket grounding
Installing one set of grounds on either side of a work site
A common cause of incidents when grounding -
Neglecting to ground across open points in a conductor, such as when lines are broken, even when grounds are installed on both sides of the break or open point.
Lines down across occupied vehicles.
People inside vehicle are usually safest to stay inside
Circumstances were occupant of an energized vehicle is safer to evacuate than to stay inside -
Fire- they must jump out as to avoid touch potential and evade step potential by landing with feet together without falling down. Then clear MAD by hopping with feet together or shuffle
Distribution transformer steps down energy to ____
120 volts
Behavior based safety principles that still apply today were pioneered by ___ in the 1930’s
Herbert Heinrich
The operative safety standard in the US that has the force of law insofar as it is a document often referenced by OSHA compliance officers in issuing citation for safety violation
ANSI Z133
Multiple causation theory
Refinement of behavioral based theory that severe injuries caused a focus of unusual non routine work, non production activities, work associeated with high energy, height, some construction activities.
In behavior based principles of accident prevention ___ percent of all industrial accidents are caused by people committing unsafe acts
88
Illistration of Herbert henrich principles of accident prevention compromising untold thousands of unsafe acts or conditions at the base of the pyramid
Accident pyramid
High reliability organizations ex.
Aircraft carriers, nuclear power plants
Stored energy ready to be released
Potential energy
Type of energy that involves the weight and height of and object
