BOSH - Lecture 7 - Electrical Safety
BOSH - Lecture 7 - Electrical Safety
BOSH - Lecture 7 - Electrical Safety
Introduction:
Electrical safety is closely related to fire safety, so we hope you do not mind hearing some things twice. Fires
are often caused by electrical trouble, as we all know, although we also know that electrical trouble can also mean
other things like electrocution and other such accidents. This module aims to introduce you to the basic terms in
electricity, occurrence mechanism of electric shock accidents and preventive measures for electric shock.
We already know that electrical safety has to do with understanding voltage, current and resistance. You and
all the other people in the workplace must understand electrical safety in order to prevent accidents/ injuries/
deaths/ property damage. Unsafe practices related to electricity have adverse effects to the human body and
property, and are the primary causes of fire.
There are practical measures that you can follow to ensure electrical safety.
Electricity
Electricity is essential and considered as among the basic needs of everybody. Electricity
had made our houses into homes, changed the mode of transportation from kalesas into taxis
and Metro Railway Transport Systems (MRTS), and improved shops to malls and factories. It is
hard to imagine if we had no electricity until now. However, it is also among the common
causes of occupational accidents resulting to injuries, death and property damage.
More than a thousand workers are killed each year by electrical shock and thousands
more are burned or maimed. More than 90% of the fatalities occurred when a person
who
was grounded made contact with live wire or an energized equipment housing. Line to line contact
accounted for fewer than 10% of the deaths.
Electrical safety requires understanding of what electricity is, how electrical energy is transferred and how the
path through which electrical current travels can be controlled.
Electricity can be defined as the flow of electrons along a conductor. Electrons are
negatively charged particles distributed in orbits around the nuclei of atoms, which
are the smallest units of an element than can exist either alone or in combination. In
an atom, the negative charge of the electrons is neutralized by the positive charge of
particles called protons, so that the atom is electrically neutral. If an external force is
applied so that the electrons are removed from their orbit and directed to a given
direction, electric current is produced in that direction.
Electric current requires a suitable circuit to provide the energy needed for lighting,
heating, etc. An electrical circuit usually contains a power source and an electrical
load. Suitable conducting material connects the power source to the load in order to
complete the electrical circuit. These conductors are covered with a suitable insulating material to prevent the
current from leaking out.
TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES – MANILA COURSE: BOSH 101
INDUSTRIAL ENGINEERING DEPARTMENT ENGR. MARIA JESSICA EBIO
Some materials such as metals have loosely bonded electrons, and the amount of thermal energy available at
room temperature is sufficient to generate free electrons. Materials that have a relatively large number of free
electrons at room temperature, which are called conductors, are capable of conducting electricity (the movement
of electrons in a given direction). On the other hand, materials that do not have a large number of free electrons
at room temperature (such as plastics), which are called insulators, are incapable of conducting electricity.
Materials that fall in between the two extremes are termed semi-conductors.
Elements of electricity
• Voltage. In order for electrons to move between two points, a potential difference must exist. The potential
difference between two points in a circuit is measured in terms of volts. The higher the potential difference, the
easier it is for the electrons to move from one point to another, and the higher the electric current.
• Resistance. The flow of electrons is also governed by the resistance offered by the conducting materials. It is
measured in Ohms.
• Current. The current flow in a circuit is measure in terms of amperes. One ampere, by definition, is the flow of
18
6.28 x 10 electrons per second past a given point in a circuit. Sometimes it is necessary to use smaller units of
measurement for the current flow, the most commonly- used units being the milliampere (0.001 ampere).
Ohm’s Law
The relationship between the elements of electricity was introduced by Mr. Georg Simon Ohm. It has been
known as the Ohm’s Law.
TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES – MANILA COURSE: BOSH 101
INDUSTRIAL ENGINEERING DEPARTMENT ENGR. MARIA JESSICA EBIO
Electrical resistance
Hazards of electricity:
• Electric shock
• Burns
• Fire
Electric shock occurrence
Electrical shock is a common hazard encountered by people involved in the installation, maintenance, and
operation of electrical equipment. Electric shock occurs once the worker’ body becomes part of an electrical
circuit when it comes in contact with a live internal conductor at the point of insulator breakdown.
The more common sources of electric shock are refrigerators and electric fans. Defective and poorly
maintained electrical device will generate electrical leak.
This leak passes all over the conductive materials of the device and if someone touches the device he will
receive electric shock.
Below are the common causes of electrical injuries/accidents:
(a) touching of live parts
(b) short circuit
(c) inadequate guarding
(d) overloading
(e) breakingofconnections
When the electric current has sufficient potential difference to overcome the body’s resistance, it results in
shock burns or even death. Although potential difference determines whether the body’s resistances will be
overcome, the damaging factor in electrical shock is the current flow.
TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES – MANILA COURSE: BOSH 101
INDUSTRIAL ENGINEERING DEPARTMENT ENGR. MARIA JESSICA EBIO
Based on the research of Charles F. Dalziel, professor at the University of California, the effects of alternating
current (60Hz) on the human body are generally accepted to be as follows:
• Let go current – the maximum current that a person can tolerate when holding a conductor and can
still free himself/herself by muscular stimulation.
• Ventricular fibrillation – most death by electric shock are caused by ventricular fibrillation. It is a
condition wherein the heart will not pulse regularly causing the heart to cease functioning. Once this
occurs, the victim will be dead in a few minutes even if the electric source is interrupted.
• Even small amounts of current can cause minor shock sensations and result to secondary accidents.
(Source: http://www.ccohs.ca/oshanswers/safety_haz/electrical.html)
There are four main types of injuries caused by electric currents – electrocution (fatal), electric shock,
burns, and falls. These injuries can happen in various ways:
• direct contact with the electrical energy.
• when the electricity arcs (jumps) through a gas (such as air) to a person who is grounded (that
would provide an alternative route to the ground for the electricity).
• thermal burns including flash burns from heat generated by an electric arc, and flame burns from
materials that catch fire from heating or ignition by electric currents. High voltage contact burns can
burn internal tissues while leaving only very small injuries on the outside of the skin.
• muscle contractions, or a startle reaction, can cause a person to fall from a ladder, scaffold or aerial
bucket. The fall can cause serious injuries.
TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES – MANILA COURSE: BOSH 101
INDUSTRIAL ENGINEERING DEPARTMENT ENGR. MARIA JESSICA EBIO
Hazardous Locations
Hazardous locations are areas where explosive or flammable gases or vapors, combustible dust, or
ignitable fibers are present or likely to become present. Such materials can ignite as a result of electrical
causes only if two conditions co-exist:
1. The proportion of the flammable substance to oxygen must permit ignition and the mixture must
be present in a sufficient quantity to provide an ignitable atmosphere in the vicinity of electrical
equipment.
2. An electric arc, flame escaping from an ignited substance in an enclosure, heat from an electric
heater, or their source, must be present at a temperature equal to or greater than the ignition
point of the flammable mixture.
Classification of Hazardous Locations
Class I – locations where flammable gases or vapors are present or likely to become present.
Class II – applies to combustible dusts.
Class III – locations are those where easily ignitable dust such as textile fibers are present but not likely to
be suspended in the air in sufficient concentration to produce an easily ignitable atmosphere.
Explosion Proof Apparatus - A device enclosed in a case that is capable of:
• withstanding an explosion of a specified gas or vapor that may occur within it
• preventing the ignition of a specified gas or vapor outside the enclosure that may be caused by
sparks, flashes or explosion of the gas or vapor inside the apparatus.
(Source: http://www.ccohs.ca/oshanswers/safety_haz/electrical.html)
A Ground Fault Circuit Interrupter (GFCI) - works by detecting any loss of electrical current in a circuit.
When a loss is detected, the GFCI turns the electricity off before severe injuries or electrocution can occur. A
painful shock may occur during the time that it takes for the GFCI to cut off the electricity so it is important to use
the GFCI as an extra protective measure rather than a replacement for safe work practices.
TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES – MANILA COURSE: BOSH 101
INDUSTRIAL ENGINEERING DEPARTMENT ENGR. MARIA JESSICA EBIO
GFCI wall outlets can be installed in place of standard outlets to protect against electrocution for just that
outlet, or a series of outlets in the same branch. A GFCI circuit breaker can be installed on circuit breaker electrical
panels to protect an entire branch circuit. Plug-in GFCIs can be plugged into wall outlets where appliances will be
used.
Test the GFCI monthly. First plug a "night light" or lamp into the GFCI-protected wall outlet (the light
should be turned on), then press the "TEST" button on the GFCI. If the GFCI is working properly, the light should
go out. If not, have the GFCI repaired or replaced. Reset the GFCI to restore power. If the "RESET" button pops out
but the light does not go out, the GFCI has been improperly wired and does not offer shock protection at that wall
outlet. Contact a qualified electrician to correct any wiring errors.
Summary:
Remember these simple safety rules to follow:
a) Do not guess
b) use proper instruments
c) always use safety device
d) lock out and tag out (LOTO)
e) never work alone
f) use danger signs
g) keep temporary electrical wiring safe
h) strictly observe rules of Philippine Electrical Code(PEC)
i) work with qualified men only
j) ensure proper maintenance
k) never bridge a fuse
l) conduct periodic electrical inspection
We hope you have become more aware of electrical safety as a result of this module.
Reference:
Department of Labor and Employment (DOLE) – Occupational Safety and Health Center (OSHC). Basic
Occupational Safety and Health Training Manual
Quote to Ponder:
“Work harder today than you think you did yesterday.” – Alex Elle