List of scientists whose names are used as SI units is the list of those scientists whose names are assigned as the names of the international units by the International Committee for Weights and Measures. The International System of Units (abbreviated SI from French: Système international d'unités) is the most widely used system of units of measurement. There are seven base units and 22 derived units[1]
(excluding compound units). These units are used both in science and in
commerce. Two of the base units and 17 of the derived units are named
after scientists.[2] By this convention, their names are immortalised. Below is the list of the scientists whose names are used as SI units.
Napier and decibel are two dimensionless units used to define relative amplitudes in logarithmic scales.[Note 4] They are not SI units, but their usage together with SI units is permitted.
Avoid contact with energized electrical circuits. Please don’t make fun of this rule if you already know this (and you probably already know if you are reading these lines) and remember that if something bad occurs – you probably won’t have second chance. That’s not funny.
Rule no. 2
Treat all electrical devices as if they are live or energized. You never know.
Rule no. 3
Disconnect the power source before servicing or repairing electrical equipment. The only way to be sure.
Rule no. 4
Use only tools and equipment with non-conducting handles when working on electrical devices. Easy to check.
Rule no. 5
Never
use metallic pencils or rulers, or wear rings or metal watchbands when
working with electrical equipment. This rule is very easy to forget,
especially when you are showing some electrical part pointing with
metallic pencil. Always be aware.
Rule no. 6
When
it is necessary to handle equipment that is plugged in, be sure hands
are dry and, when possible, wear nonconductive gloves, protective
clothes and shoes with insulated soles. Remeber: gloves, clothes and shoes.
Safety clothes, gloves and shoes
Rule no. 7
If
it is safe to do so, work with only one hand, keeping the other hand at
your side or in your pocket, away from all conductive material. This
precaution reduces the likelihood of accidents that result in current
passing through the chest cavity.
If you ever read about current passing through human body you will know, so remember – work with one hand only. If you don’t clue about electric current path through human body, read more in following technical articles:
Minimize the use of electrical equipment in cold rooms or other areas where condensation is likely. If equipment must be used in such areas, mount the equipment on a wall or vertical panel.
Rule no. 9
If water or a chemical is spilled onto equipment, shut off power at the main switch or circuit breaker and unplug the equipment. Very logical. NEVER try to remove water or similar from equipment while energized. Afterall, it’s stupid to do so.
Rule no. 10
If
an individual comes in contact with a live electrical conductor, do not
touch the equipment, cord or person. Disconnect the power source from
the circuit breaker or pull out the plug using a leather belt.
Tricky situation, and you must be very calm in order not to make the situation even worse. Like in previous rules – Always disconnect the power FIRST.
Always disconnect the power FIRST
Rule no. 11
Equipment producing a “tingle” should be disconnected and reported promptly for repair.
Rule no. 12
Do
not rely on grounding to mask a defective circuit nor attempt to
correct a fault by insertion of another fuse or breaker, particularly
one of larger capacity.
Rule no. 13
Drain capacitors before working near them and keep the short circuit on the terminals during the work to prevent electrical shock.
Rule no. 14
Never touch another person’s equipment or electrical control devices unless instructed to do so. Don’t be too smart. Don’t try your luck.
Rule no. 15
Enclose all electric contacts and conductors so that no one can accidentally come into contact with them. If applicable do it always, if not be very carefull.
Rule no. 16
Never handle electrical equipment when hands, feet, or body are wet or perspiring, or when standing on a wet floor. Remeber: Gloves and shoes
Rule no. 17
When it is necessary to touch electrical equipment (for example, when checking for overheated motors), use the back of the hand. Thus, if accidental shock were to cause muscular contraction, you would not “freeze” to the conductor.
Rule no. 18
Do not store highly flammable liquids near electrical equipment.
Rule no. 19
Be
aware that interlocks on equipment disconnect the high voltage source
when a cabinet door is open but power for control circuits may remain
on. Read the single line diagram and wiring schemes – know your switchboard.
Rule no. 20
De-energize open experimental circuits and equipment to be left unattended.
Rule no. 21
Do not wear loose clothing or ties near electrical equipment. Act like an electrical engineer, you are not on the beach.
Example of human stupidity and ignorance of basic safety
Electrical safety, come on… I guess we’ll never know did the cord extension drop into water… Hope not.
Example of stupiditySource:http://electrical-engineering-portal.com/21-safety-rules-for-working-with-electrical-equipment
Electric current passing through the body, particularly alternating current
at power frequencies of 50 Hz and 60 Hz, may disrupt the nervous
system, causing muscular reaction and the painful sensation of electric shock. The most common reaction is to be thrown off the conductor as a result of the muscular contraction.
However,
in a small number of instances, the consequence is death from cardiac
arrest, or from ventricular fibrillation (where the heart muscle beats
in a spasmodic and irregular fashion) or from respiratory arrest.
The psychological effects
are largely determined by the magnitude and frequency of the current,
the waveform (for example, continuous sine wave, or half wave rectified
sine wave, or pulsed waveform), its duration, and the path it takes
through the body.
An authoritative guide on the topic is published in IEC 60479. The following text concentrates on the most common situation of a shock from a continuous power frequency ac waveform.
The
magnitude of the current is the applied voltage divided by the
impedance of the body. The overall circuit impedance will comprise the
body of the casualty and the other components in the shock circuit,
including that of the power source and the interconnecting cables. For
this reason, the voltage applied to the body, which is commonly known as
the touch voltage, will often be lower than the source voltage.
The impedance of the body is determined by the magnitude of the touch voltage (there being an inverse relationship between impedance
and voltage) and other factors, such as the wetness of the skin, the
cross-sectional area of contact with the conductors, and whether or not
the skin is broken or penetrated by the conductors.
As a general rule of thumb, at an applied voltage of 230 V at 50 Hz,
the total body impedance for a hand-to-feet path will be in the range
1000 Ω to 2500 Ω for most of the population, falling to around 750 Ω at
voltages in excess of about 1000 V. Figure 16.1 - Depiction of a typical indirect contact electric shock The path that the current takes through the body has a significant effect on the impedance.
For example, the impedance for a hand-to-chest path is in the order of
50 per cent of the impedance for a hand-to-foot path. Moreover, the
current’s path through the body is a significant determinant of the
effect on the heart.
Table 16.1 summarizes the physiological effects of current passing through the body.
The effects relate to a hand-to-hand shock exceeding 1 s for a person in good health. If the duration were less than 1 s, greater currents could be tolerated without such adverse reactions.
Electric shock accidents are most common on low-voltage systems
and are usually subdivided into two categories of direct contact and
indirect contact shocks. A direct contact shock occurs when conductors
that are meant to be live, such as bare wires or terminals, are touched.
An indirect contact shock occurs when an exposed conductive part that
has become live under fault conditions is touched, as depicted in Fig.
16.1.
Examples of an exposed conductive part are the metal casing
of a washing machine and the metal casing of switchgear. This type of
accident, which requires two faults to occur (the loss of the earth connection followed by a phase-to-earth fault), is quite common.
Physiological Effects
Table 16.1 The effect of passing alternating current (50 Hz) through the body from hand-to-hand
Current (mA)
Physiological effect
0.5–2
Threshold of perception
2–10
Painful sensation, increasing with current. Muscular contraction may occur, leading to being thrown-off
10–25
Threshold
of ‘let go’, meaning that gripped electrodes cannot be released once
the current is flowing. Cramp-like muscular contractions. May be
difficulty in breathing leading to danger of asphyxiation from
respiratory muscular contraction
25–80
Severe
muscular contraction, sometimes severe enough to cause bone dislocation
and fracture. Increased likelihood of respiratory failure. Increased
blood pressure. Increasing likelihood of ventricular fibrillation
(unco-ordinated contractions of the heart muscles so that it ceases to
pump effectively). Possible cardiac arrest
Over 80
Burns
at point of contact and in internal tissues. Death from ventricular
fibrillation, cardiac arrest, or other consequential injuries
First Aid with Emergency Defibrillator
First aid - Emergency defibrillator When
providing first aid to an electric shock casualty, the first action
should be to remove the cause by switching-off the supply or otherwise
breaking contact between the casualty and the live conductor. Cardiopulmonary resuscitation may be required.
If
the casualty is suffering from ventricular fibrillation, the only
effective way to restore normal heart rhythm is by the use of a
defibrillator.
Where a defibrillator is not immediately
available, the first aider should carry out cardiopulmonary
resuscitation until either the casualty recovers or professional
assistance arrives. SOURCE: J.M. Madden
