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VI. Safe Handling of Equipment Proper use and maintenance of
laboratory equipment are essential to laboratory safety. Equipment should be
regularly inspected to ensure proper maintenance. Many laboratory accidents
can be attributed to improperly maintained or improperly used laboratory
equipment.
1. Type Use the
correct type of glass. a. When heating
glassware, make sure to use only glassware made of borosilicate glass (Pyrex®
brand or Kimax® brand). Common glass can break,
explode or shatter very easily when subjected to heat shock. b. Make sure to use
test tubes made of borosilicate glass when heating. Not all test tubes are
made of borosilicate glass. 2. Proper Use Each
type of glassware has its proper use and should be used only for its intended
purpose. a. For measuring
volume:
b. For storing
solids and liquids:
c. For containing
reactive chemicals during experiments:
d. For transferring
liquids and gases:
e. For measuring
temperature:
3. Cleaning Keep
glassware clean. a. Clean immediately
after use. The longer glassware sits, the harder it is to clean. b. Use
laboratory-grade detergents for cleaning glassware. Chromic Acid
(dichromate/sulfuric acid mixture) should never be used to clean glassware. c. Be sure to rinse
glassware well. d. When using
brushes, make sure the metal part of the brush does not scratch the glass. 4. General Cautions a. Use glassware
that is without defect and has smooth edges. b. Glassware should
have no cracks, chips, or scratches. In particular, be wary of “star cracks”
that can form on the bottom of beakers and flasks. Any glassware with such
cracks should be properly disposed of immediately. c. All glass tubing
should be fire-polished. d. Never set hot
glassware on cold surfaces or in any way change its temperature suddenly.
Even a Pyrex® or Kimax® beaker will break if cold
water is poured into a hot beaker. 5. “Frozen” Glass Be
careful with glassware that is “frozen.” Only teachers, wearing goggles and
gloves, should try to release the “frozen” glassware. If this fails, discard
the glassware. Some common cases of “frozen” glassware are: a. nested beakers that have been jammed together. b. stoppers that cannot be removed from bottles. c. stopcocks that cannot be moved. 6. Hot Glass a. Use care when
working with hot glass. Hot glass looks exactly the same as room temperature
glass. b. Do not leave hot
glassware unattended, and allow ample time for the glass to cool before
touching. c. Check the
temperature of the glassware by placing your hand near, but not touching, the
potentially hot glass. d. Have hot pads,
thick gloves, or beaker tongs available for grasping hot glassware. 7. Glass Tubing a. Breaking. Use
gloves or towels to protect hands when breaking glass tubing. Use goggles to
protect the eyes. Here are the steps for properly breaking glass tubing.
i.
Scratch the glass once with a file or score.
ii.
Wrap the glass in a towel.
iii.
Place the thumbs together opposite the scratch.
iv.
Pull and bend in one quick motion.
v.
Fire polish the broken ends:
hold the glass so that the sharp end is in the top of the flame of a gas
burner. Rotate the tube so all sides are heated evenly, causing the sharp
edges to melt and become smooth. Place the glass on insulating material to
cool. b. Bending. Bending
glass tubing is often necessary. Follow these procedures:
i.
Place a wing-top attachment on a gas burner and heat the area
of the glass to be bent while holding it with one hand on each end, rotating
to ensure even heating.
ii.
When the glass is soft and pliable, remove it from the flame
and quickly bend to the desired shape. Results will improve with practice.
iii.
Place on insulating material until cool. 8. Disposal Defective
glassware should be disposed of correctly. a. Glassware should
be disposed of in a separate container from normal trash. Such container
should be clearly labeled BROKEN GLASSWARE ONLY. b. When handling
broken glassware, wear gloves or use a dustpan and broom. Do not pick up
broken glass with bare hands. 1. Proper Stoppers a. Use corks for
sealing organic solvents. b. Use rubber
stoppers for sealing aqueous solutions. 2. Inserting
Thermometers and Glass Tubing a. Check that the
hole is the correct size. b. Protect your
hands with leather gloves. c. Lubricate the
hole with glycerin or soapy water before inserting thermometers or glass
tubing. d. During the
insertion process, keep a short distance between the stopper and the hand
holding the glass. e. Use a rotary
motion to guide the glass through the stopper. f. Remove
thermometers immediately after use. If they are difficult to remove,
carefully cut away the cork or stopper. 1. Alcohol
Thermometers If glass
thermometers are being used, it is highly recommended that they be alcohol
filled. Mercury thermometers should be phased out as quickly as possible. If
mercury thermometers must be used for purposes of higher accuracy, it is
recommended that Teflon® coated thermometers be used. •See
Chapter VIII.B.4, Mercury Spills. 2. Resistance
Thermometers Resistance
thermometers, or temperature probes, should be considered as alternatives to
glass thermometers. 3. Rules for Using
Thermometers a. Never use a
thermometer as a stirring device. b. Never swing or
shake down a thermometer. c. Never use an open
flame on a thermometer bulb. d. Use extreme care
when inserting or removing a thermometer from a rubber stopper. e. Mercury
thermometers should not be used in heated ovens where breakage might easily
occur. f. Don’t place thermometers
where they are likely to roll or be knocked off a table. All thermometers
should have anti-roll devices. g. Make sure you
choose a thermometer with an appropriate temperature range. Overheating a
thermometer can cause breakage of its reservoir. Where possible, use electric hot
plates in place of gas burners (Bunsen, portable propane, and butane).
Alcohol burners should never be used as a heat source. 1. Safety Rules for
Using Gas Burners a. Make sure you
know the location of the master gas shut-off valve. b. Match the type of
burner to the type of gas available. c. Make sure all
students know how to operate the burner safely. d. Make sure there
are no leaks in rubber hoses connecting the source to the burner. e. Keep rubber hoses
away from the flame f. A soft rubber
hose connection from a gas burner to the gas outlet is better than a
semi-rigid, woven cover type connector, as this lessens the danger of
tipping. g. Use a ceramic-centered (not asbestos-centered) wire gauze
under the object to be heated to distribute the heat evenly. h. Use matches or
lighters instead of strikers for lighting burners. Light matches or lighter
before turning on the gas. Bring flame to the side of the top opening of the
barrel while slowly turning on the gas. i. Turn off the gas
if the gas “flashes back” or burns at the burner base. j. Do not lean
toward or reach across a flame. k. Never leave
anything unattended while it is being heated or is reacting rapidly. l. Remember that the
gas burner barrel remains hot long after use. m. If wing tops
(flame spreaders) are used, allow time for these to cool before removing them
from the gas burner. n. Turn off gas
valves before leaving work area. 2. Safety Rules for
Using Electric Hot Plates a. Use a hot plate
with a smooth, clean surface. b. Hot plates appear
exactly the same whether hot or at room temperature. Always assume they are
hot and act accordingly. c. Keep the
electrical cord of a hot plate away from water and the heating surface. d. The cord of the hot
plate should be checked periodically for frays and faults. Any hot plate with
faulty wiring should not be used. It should be repaired or replaced
immediately. 3. Safety Rules for
All Heating Processes a. Never heat a
closed container. b. Never point the
open end of a test tube toward anyone. c. Never look into
the open end of a heated test tube. d. Test tubes should
be held with a test tube holder and heated gently along the side, not at the
bottom, to minimize superheating. e. Any set-up should
be designed to allow for fast removal of the heat source. f. Do not clamp test
tubes or flasks more tightly than necessary to hold them in place when
heating. Expanding glass may break if clamped too tightly. 1. Refrigerators and
freezers used for the storage of chemical reagents and/or biological
materials should never be used for the storage of food. 2. Flammable
materials should be stored in the flammable material cabinet and not in the
refrigerator. 3. A sign should be
placed on the refrigerator as a warning not to store flammable and other
inappropriate materials inside. 1. Treat all
circuits as though they were energized. 2. Make sure power
is off when connections are made. 3. All electrical
equipment should be grounded through three-prong plugs. 4. Use ground fault
circuit interrupters (GFCIs) throughout all laboratories. 5. Test all
electrical receptacles and emergency cutoff switches annually for correct
wiring and functioning. 6. Test all electrical
apparatus annually for voltage leaks. 7. Inspect all
electrical cords annually for defects and damage. 8. Keep work areas
dry when working with electrical apparatus. Pipets are useful for measuring
and dispensing liquids. The following rules apply to all types of pipets,
including volumetric pipets, graduated pipets, Pasteur pipets, micro-pipets,
and automatic dispensing pipets. 1. Never put a pipet
in your mouth. 2. Draw the liquid
into the pipet using a rubber bulb or pipet pump. 3. Never withdraw a
liquid from a near-empty container. If you attempt to fill a pipet under
conditions where air can enter the pipet, the liquid will shoot up into the
bulb or pump. 4. Never lay a pipet
flat on a table or turn upside down with the bulb or pump attached. The
liquid will flow into the bulb/pump, contaminating the bulb/pump. 5. Dispose of broken
pipets in the appropriate glass-disposal container. Vacuums occur in the laboratory
usually in two situations: using a vacuum pump or by condensing vapors in a
closed system (e.g., “crushed soda can” demonstration). 1. Place guards
around glass containers in which a vacuum might be created. 2. Always design a
relief device such as a stopcock into any vacuum system. The device should
allow the slow infusion of air into a system under vacuum. 3. Avoid reactions
or procedures in completely closed systems. 4. Any glassware
that will be subjected to a vacuum should be specifically designed with heavy
walls. 5. Properly handle
and maintain vacuum pumps: a. change the oil on
a regular basis; b. always have a
trap attached; c. have belt guards around belts and pulleys. I. Centrifuges (Macro and Micro) The centrifuge should always be securely
anchored by use of suction cups or wheel brakes. The centrifuge should have a
safety shield and a top disconnect switch. Other safety procedures include
the following: 1. Inspect glass
tubes for cracks. 2. Inspect the metal
centrifuge cups for roughness. 3. Position test
tubes opposite each other with the same weight in each tube to balance the
centrifuge. Use water-filled tubes as necessary for balance. An unbalanced
centrifuge can “walk” off the table. 4. If the centrifuge
has a lid, make sure it is closed during operation. 5. Keep hair, loose
clothing, and body parts away from the centrifuge while it is operating. 6. A spinning
centrifuge should not be touched for any reason. Do not try to stop a
centrifuge by grabbing it. Makes sure the centrifuge is completely stopped
before removing test tubes from it. Note: Schools should only purchase
centrifuges equipped with a safety feature that does not allow the devices to
be opened until the spinning has stopped. 7. Make sure that
the centrifuge operates vibration-free at the top speed. 8. Never leave a
running centrifuge unattended. 9. Keep rotors and
buckets clean. Nonflammable cryogenics (e.g.,
liquid nitrogen and dry ice) can be educational but are dangerous and should
be handled only by the teacher. Liquid nitrogen requires special ventable flasks or Dewars (to
minimize risk of an explosion). Such flasks can break easily if handled
carelessly. Use chemical splash safety goggles at a minimum (complete face
shield is better), thick gloves and long sleeves when working with either of
these substances. It is important that students observing demonstrations wear
eye protection and be seated at a safe distance from the demonstration. Compressed gases can present
dangers through toxicity, reactivity or flammability of the gas, or because
the gas is pressurized. Even a normally “safe” gas, such as nitrogen, can
become a safety hazard when compressed. An improperly used gas cylinder is a
potential bullet or rocket. 1. Have proper carts
available for transporting gas cylinders. Do not roll large cylinders around. 2. Use the proper
tank and fittings designed for each gas. Your gas supplier will be able to
help you with this. 3. Asphyxiation is
the most subtle danger of working with compressed gases. Always use
compressed gases in a well-ventilated area. 4. Always make sure
tanks are secure. No compressed gas tank should be allowed to stand free. All
tanks should be strapped or tightly chained to a rigid support to prevent accidental
toppling. 5. Keep electrical
lines away from compressed gas tanks. 6. Keep gas tanks
away from heat sources. 1. Electric Shock The use
of microcomputers in the science laboratory is increasing at a rapid rate.
Although the programming and use of software with computers is not hazardous,
many applications that require electrical connections to the computer may
involve the risk of electrical shock. Below are guidelines for working with
computers. a. When the internal
electronics must be exposed to make connections, unplug the computer. Most
computer circuitry operates on low voltage direct current, but higher A.C.
and capacitors are present in the power supply as well as the VDT (Video
Display Terminal). b. Whenever
possible, students should only make connections to external connection ports
(i.e., game paddle connectors, exposed edge connectors). Often it is possible
to use low voltage extension cables from inside the computer to an outside
location to reduce the risk of accidental shock while making connections. c. Some applications
require use of 110 volt relays, heaters, etc., and all normal precautions for
use of these devices should be followed. Be aware that the computer may
remotely turn these devices on unexpectedly. 2. Ergonomics Some
study should be given to the physical arrangement of the keyboard, video
display, and lighting. Muscle fatigue and eye strain can be reduced by the
appropriate positioning and adjustment of these components. Care should always be taken when
dealing with sharp objects. Scissors, needle probes, and knives should be
used with extreme care. Sharps to be discarded – and any other items having
sharp edges or points – should be placed in a separate, rigid container
labeled SHARPS ONLY.
1. Always keep your
work space free of clutter. 2. Apparatus
attached to a ring stand should be positioned so that the center of gravity
of the system is over the base and not to one side. 3. Apparatus, equipment,
or chemical bottles should not be placed on the floor. 4. Whenever
hazardous gases or fumes are likely to be evolved, the operation should be
confined to a fume hood. 5. Any problems with
glassware, equipment, chemicals, etc. should always be reported immediately
to the instructor. 6. High/low pressure
situations (e.g., pressurized systems for specialized reactions, or vacuums)
can present hazards. Only sound glassware should be subjected to such
situations. •See
Chapter III, Safety Concerns and Emergency Laboratory Equipment, and Chapter
V, Safety Strategies in the Classroom, for related ideas on safety practices. |
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