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SourceMaterialTomerge/tsysShopmanual/safety.md

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+**Lab Safety**
+
+
+**Acquaint yourself with the location of the following safety items
+within the lab.**
+ 
+
+1.   Fire extinguisher
+2.   First aid kit
+3.   Telephone and emergency numbers : Make sure that you have handy
+    emergency phone numbers to call for assistance if necessary. The
+    number for  emergencies is on campus is **511**. (No need to dial 8
+    for this number). If any safety questions arise, consult the lab
+    instructor or staff for guidance and instructions.
+
+\
+Observing proper safety precautions is important when working in the
+laboratory to prevent harm to yourself or others. The most common hazard
+is the electric shock which can be fatal if one is not careful.
+
+### Electric shock
+
+Shock is caused by passing an electric current through the human body.
+The severity depends mainly on the amount of current and is less
+function of the applied voltage. The threshold of electric shock is
+about 1 mA which usually gives an unpleasant tingling. For currents
+above 10 mA, severe muscle pain occurs and the victim can\'t let go of
+the conductor due to muscle spasm. Current between 100 mA and 200 mA (60
+Hz AC) causes ventricular fibrillation of the heart and is most likely
+to be lethal.
+
+What is the voltage required for a fatal current to flow? This depends
+on the skin resistance. Wet skin can have a resistance as low as 150 Ohm
+and dry skin may have a resistance of 15 kohm. Arms and legs have a
+resistance of about 100 Ohm and the trunk 200 Ohm. This implies that 110
+V can cause about 160 mA to flow in the body if the skin is wet and thus
+be fatal. In addition skin resistance falls quickly at the point of
+contact, so it is important to break the contact as quickly as possible
+to prevent the current from rising to lethal levels.
+
+ 
+
+Equipment grounding
+
+Electric instruments and appliances have equipment cases that are
+electrically insulated from the wires that carry the power. The
+isolation is provided by the insulation of the wires as shown in the
+figure a below. However, if the wire insulation gets damaged and makes
+contact to the case, the case will be at the high voltage supplied by
+the wires. If the user touches the instrument he or she will feel the
+high voltage. If, while standing on a wet floor, a user simultaneously
+comes in contact with the instrument case and a pipe or faucet connected
+to ground, a sizable current can flow through him or her, as shown in
+Figure b. However, if the case is connected to the ground by use of a
+third (ground) wire, the current will flow from the hot wire directly to
+the ground and bypass the user as illustrated in figure c.
+
+![shockimage](shock.gif){width="423" height="331"}
+
+Equipment with a three wire cord is thus much safer to use. The ground
+wire (3rd wire) which is connected to metal case, is also connected to
+the earth ground (usually a pipe or bar in the ground) through the wall
+plug outlet.
+
+**Safety Precautions**\
+ 
+
+-   -Do not work alone while working with high voltages or if you are
+    using electrically operated machinary like a drill.
+-   -Never leave high voltages on when you are not present.
+-   -Keep one hand in your pocket when probing high voltage circuits or
+    discharging capacitors.
+-   -Make sure all high voltage connections are adequately taped or
+    otherwise insulated to prevent accidental contact by you or
+    neighboring students.
+-    -After switching power off, discharge any capacitors that were in
+    the circuit. Do not trust supposedly discharged capacitors. Certain
+    types of capacitors can  build up a residual charge after being
+    discharged. Use a shorting bar across the capacitor, and keep it
+    connected until ready for use.
+-   -If you use electrolytic capacitors, do not
+-   -   put excessive voltage across them
+    -   put ac across them
+    -   connect them in reverse polarity
+
+-   -Take extreme care  using tools that can cause short circuits if
+    accidental contact is made to other circuit elements. Only tools
+    with insulated handles should be used.
+-   -If a person comes in contact with a high voltage, immediately shut
+    off power. Do not attempt to remove a person in contact with a high
+    voltage unless you are insulated from them.
+-   -In the event of an electrical fire do not use water. The lab fire
+    extinguishers are specifically charged for electrical fires. Vacate
+    the lab and close the door. Do not breath toxic smoke or fumes. Ring
+    the fire alarm, if one is available.
+-    -Check wire current carrying capacity if you will be using high
+    currents. The lab power wiring can only handle 15 Amperes
+    continuously.
+-   -Make sure your leads are rated to withstand the voltages you are
+    using. This includes instrument leads.  Common wire insulation is
+    rated for 600 Volts.
+-   -Avoid simultaneous touching of any metal chassis used as an
+    enclosure for your circuits and any pipes in the laboratory that may
+    make contact with the earth, such as a water pipe. Use a floating
+    voltmeter to measure the voltage from ground to the chassis to see
+    if a hazardous potential difference exists.
+-   -Make sure that the lab instruments are at ground potential by using
+    the ground terminal supplied on the instrument.