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XI. Physics Experimental physics motivates
teachers and students to create new techniques and apparatus and to use them to
demonstrate both old and new ideas. It is impossible, therefore, to
anticipate all of the specific hazards that might arise in the study of
physics. While it is not desirable to eliminate creativity in the interest of
safety, teachers should temper their creativity with a constant alertness to
potential dangers. Common sense can go a long way toward providing a safe
environment. This chapter provides both general and specific rules for those
activities frequently performed in the high school physics classroom.
1. Exposed Belts Exposed
belts and pulleys must be covered with a shield. This prevents the hazard of
broken belts, and of fingers or clothing being caught between belts and
pulleys. (OSHA Regulations: 29 CFR 1910.219) The
following website offers more information on this topic: 2. Falling Masses Heavy
masses may be used in experiments involving Atwood’s machine, free fall,
Newton’s laws, and momentum. Warning should be given to students to prevent
hands and feet from being caught between a moving heavy mass and floor or
table surfaces. Students may not anticipate how difficult it is move or
support a lead brick or kilogram mass. 3. High-speed
Rotation Rotators
are sometimes used to demonstrate centripetal force, circular motion, and
sound phenomena. Any device attached to a rotator should be fastened securely
and checked for tightness frequently. Observers should avoid contact with
moving accessories such as toothed wheels, siren discs, etc. Loose clothing
and long hair should be kept away from moving parts, and observers should not
be in the plane of rotation. The use of safety goggles should be considered
in student laboratories investigating centripetal force. Extremely high-speed
rotation should be avoided when possible. High speeds may cause some objects
to fly apart unexpectedly. A strobe
light is sometimes used to illuminate a rotating object, making the object
appear to be at rest. If the object is a fan blade, a toothed wheel, or
anything else with sharp edges, there is danger of injury from touching or
inserting an object into the apparently stationary object. Students should be
alerted to this danger. 4. Magnets Large
permanent magnets and electromagnets may attract opposite poles or steel
objects with unanticipated force. Students should be warned of the potential
risk of pinching their hands between object and the magnet. In addition,
exposed terminals on electromagnets should be insulated to prevent electric
shock hazards. 5. Power Tools It may
be necessary for students constructing apparatus for physics experiments to
use various power tools contained in a wood or metal shop. In these
situations the industrial arts instructor should be consulted for proper
safety precautions necessary for each tool or machine. 6. Projectiles In
demonstrating the flight of any projectile, students should be kept clear of
the path and impact area. The teacher should always pretest the projectile to
determine the path it will follow and its range as well as the amount of
variability to be expected. Sharp-pointed objects should not be used as
projectiles. Use of safety goggles should be considered. A simple mechanical
launcher (e.g., compressed spring, compressed air, stretched elastic) should
be used. It should only be "loaded" at the specific time a flight
is to be observed. 7. Springs Stretched
or compressed springs contain mechanical potential energy. A stretched
spring, unexpectedly released, can pinch fingers. A compressed spring, when
suddenly released, can send an object at high velocity toward an observer.
Care should be taken to avoid unexpected release of the spring’s energy when
working with dynamics carts, spring-type simple harmonic oscillators, and
springs used in wave demonstrations. 1. Physiological
Effects a. Body Resistance. Students must be
warned of the high death potential present even when the voltage is low. The
severity of an electrical shock depends primarily on the amount of current to
which a person is exposed. Since the current is related to the resistance and
voltage, these two factors, as well as the part of the body involved and the
duration of the contact, determine the extent of injuries to the victim. If
the skin is wet or the surface broken, the resistance drops off rapidly,
permitting the current to flow readily through the bloodstream and body
tissues. See
chart below for relative hazards of electric shock.
b. Current-Resistance
Relationship. Ohm’s law indicates that the amount of current in amperes
flowing in a circuit varies directly with the electrical potential applied in
volts (V) and varies inversely with the resistance (R) in ohms:
I = V/R Thus,
one can calculate the expected current in a given situation. Example:
Let R for a damp hand = 1,000 ohms. If an electrical potential of 110 volts
is applied across the hand, the current would be:
The table below illustrates how the
various current values affect human beings. The readings are approximate and
vary among individuals. In view of the information below, it would be sound practice
never to receive an electrical shock under any circumstances if it can be
avoided.
c. Burns. Many electrical
devices become quite hot while in use. In addition, "shorted" dry
cells and batteries can produce very high temperatures. Students should never
grasp a recently operated device or wiring without first checking for excess
heat. 2. Electrical
Apparatus a. Batteries. A battery is an
unregulated source of current capable of producing large currents when
resistance is low. When short-circuited, connecting wires can become very
hot, raising the risk of burns. Short-circuited mercury batteries may even
explode. Chemical leakage from batteries is a potential hazard, especially in
the case of wet cells that contain caustic chemicals such as sulfuric acid. Certain
types of batteries are rechargeable while others are not. Carbon-zinc and
nickel-cadmium type batteries can be recharged. Do not, however, attempt to
recharge a completely dead carbon-zinc battery, a leaking or corroded
battery, or any battery that carries a warning against recharging. Such
batteries can cause damage to the charger and may explode, causing personal
injury. Lead-acid batteries can be recharged but produce explosive hydrogen
gas during the process. They should only be recharged in a well-ventilated
area with an appropriate charger. b. Capacitors. Capacitors are
used to store electric charge. They may remain charged for long periods after
power is turned off, and they therefore pose a serious shock/burn hazard.
Before working on any circuit containing a capacitor, make sure that it is
discharged by shorting its terminals with an insulated wire or screwdriver.
Oil-filled capacitors may sometimes recharge themselves and should be kept
shorted when not in use. Oil from older capacitors may be contaminated with
dangerous PCBs. When installing electrolytic-type capacitors in a circuit,
proper polarity rules must be followed (negative to negative and positive to
positive). Improper connection can result in an explosion. Be on the lookout
for capacitors in any apparatus with high voltage components such as
oscilloscopes, TV sets, lasers, computers, and power supplies. Electrostatic
generators and Leyden Jars are also capacitors and can be a source of
unexpected shock. c. Circuit Loads - Most school
laboratory electrical circuits have a maximum power rating of 1,500 watts (if
fuses are 15 amp) or 2,000 watts (if fuses are 20
amp). The total power load on a circuit should not exceed these values. The
total load is the sum of the power ratings of all apparatus plugged into that
circuit. The individual power rating is usually found printed on a plate
somewhere on the apparatus. d. Electrostatic
Generators. Electrostatic generators used in demonstrations of static
electricity produce high voltages (about 105 volts) with very low
currents. The danger of these generators depends on their size and capacity
to produce enough current to be dangerous. In many cases the shock from such
devices is very quick and not harmful. The startling effect, however, can be
detrimental to persons with heart conditions. In
general, experiments that use human subjects to demonstrate the effect of
electrical shock should not be attempted due to the large variation in
physical and physiological factors. Leyden jars -- which can be charged with
electrostatic generators -- are especially dangerous because of their
capacity to store a charge for long periods of time. An accidental discharge
through a person can be avoided by properly shorting the devices after use e. Extension Cords. Use extension
cords only when there is no convenient way to connect equipment directly to a
receptacle. If an extension cord must be used, it should be checked for
damage, proper grounding, and electrical capacity. An extension cord should
be marked with its capacity in amperes and watts and the total load should
not exceed these values. If the cord is unmarked, assume that it is 9 amperes
or 1,125 watts. If an extension cord becomes very warm to the touch, it
should be disconnected and checked for proper size. In general, science
laboratories should be equipped with sufficient receptacles to minimize
extension cord use. •See
Chapter XI.B.2.c, Circuit Loads. f. Fuses/Circuit
Breakers. Replace blown equipment fuses with fuses of the same amperage.
Replace fuses with the equipment unplugged. Failure to use the correct fuse
can cause damage to equipment and overheating. Frequent blowing of circuit
fuses or tripping of circuit breakers usually indicates that the circuit is
overloaded or a short exists. Circuit breakers and fuses that are tripped or
blown should be turned on or replaced only after the cause of the short or
overload is removed from the circuit. g. Grounding. Use grounded
3-prong plugs when available. If the outlet is 2-prong, use an adapter and
secure the ground wire to the cover-plate screw on the outlet. Grounding is
particularly important for the light sources used with ripple tanks since
these lights are suspended above the water in the tanks. Any apparatus with a
metallic case or exposed metal parts should be checked to make sure that the
case is grounded. Such ungrounded appliances should be retrofitted with a
ground wire and three-pronged plug. The use of ground-fault interrupters
should be considered. h. Power Cords. Any power cord
should be inspected periodically and replaced immediately if frayed or
damaged. Apparatus should be located to keep power cords away from student
traffic paths. When removing the cord from an outlet, the plug should be
pulled, not the power cord. Wet hands and floors present a hazard when
connecting or disconnecting electrical apparatus. C. Vacuum and Pressure Hazards 1. Vacuums a. Suitable
Containers. Many popular physics demonstrations utilize a small vacuum
pump to evacuate a chamber such as a bell jar, a coin-feather tube, or a
collapsing metal can. Under no circumstances should a standard thin-walled,
flat-bottom jar be evacuated because of the likelihood of implosion. If
students are to be allowed to pump out a well-designed chamber, make sure it
is firmly mounted so it cannot tip over and implode when under vacuum. Any
large evacuated chamber should be equipped with a screen shield to help
provide protection following an implosion. Such implosions can result from
long-term stresses in glass or may result from thermal effects if heating
occurs without opportunity to expand. On small chambers where a screen is
inconvenient or undesirable, the walls should be wrapped with tape to reduce
the flying glass following an implosion. When bell jars are used in demonstrations,
remind students that they are specifically designed to withstand atmospheric
pressure, and that one should never pump on a conventional container. Full
face shields should be worn whenever working with a system which could
conceivably implode or explode. b. Tubes and
Implosions. Vacuum tubes, especially large ones, present a safety hazard
if the tube breaks. Flying glass and electrodes can travel great distances
when a tube implodes. This is a particular danger when tubes such as a
cathode ray tube, a TV picture tube, or a Crookes tube are used in a
demonstration or experiment that removes them from a protective housing.
Under these conditions, safety goggles or shields should be worn by all
observers. When an
inoperable tube is to be discarded, it should be covered with a heavy canvas
cloth and broken by striking the rear of the tube with a hammer. The broken
tube should then be carefully disposed of. c. Vacuum Pumps. Vacuum pumps
equipped with belts and pulleys must have the belt and pulley system shielded
to prevent clothing and hands from getting caught. This shield should also
prevent injury from broken belts striking nearby observers. Students should
be warned to be careful of the hot motor and other parts after operation.
(OSHA Regulations: 29 CFR 1910.219). The
following website offers more information on this topic: 2. Pressures a. Compressed Air. Students in
laboratories equipped with compressed air at lab stations or lecture tables
should be warned of the danger of blowing dust or other debris into the eyes
accidentally with compressed air. High pressure air directed at glassware for
drying purposes can provide enough force to knock containers from the hands.
The flow of air should be adjusted first to prevent this hazard. b. Gas Bottles. One of the most
common items to be found in any science laboratory is a container of
compressed gas. The pressures in gas containers may vary from atmospheric
pressure to 10,000 psi, with most tanks essentially designed as shipping
containers (with a minimum weight and wall thickness). A container of gas
should not be kept around if the gas and its characteristics are unknown. Any
gas cylinder should be anchored to the wall or mounted in a well-designed
holder. When a gas cylinder tips over and is damaged, it can become a high
powered, massive rocket capable of going through many walls and people. Large
tanks URL 66should be carefully moved in a wheeled cart with a tie-down chain
safety cap in place, and should never be pulled by the threaded cap or rolled
on the floor. (OSHA Regulations: 29 CFR 1910.101). The
following website offers more information on this topic: Almost
all cylinders have internal pressures greatly exceeding what is needed for an
experimental apparatus. Small laboratory lecture bottles may be controlled
with a needle valve as long as they are not discharging into a system
allowing pressure to build up to bottle pressure. Large cylinders should be
controlled by a single or double stage regulator of a suitable pressure
range. When a regulator is being used, the main cylinder valve should still
be closed each time an experiment is shut down since regulators are not made
to be reliable shut-off valves. If
compressed gas is used as a propellant, students should remain clear of the
gas exhaust and propelled objects. •See
Chapter XI.A.6, Mechanical Hazards-Projectiles. c. Generating Gases. A pressure
relief safety valve of some type should be an integral part of any system
constructed to generate gas or steam. 1. Heat a. Heating
Procedures. Often it is necessary to heat liquids and solids in physics
experiments and demonstrations. It is safer to use water baths and hot plates
than to heat directly with open flames such as with Bunsen burners. Below are
guidelines for heating and handling hot objects.
i.
Any glass apparatus that is to be heated should be made of
Pyrex® brand or Kimax® brand. It must be free of chips and cracks.
ii.
Gas burners should be kept away from the body at all times.
The pressure of the gas should be adjusted to allow proper ignition. Too high
a pressure tends to blow the flame out. Do not allow gas to accumulate if
ignition is delayed for any reason.
iii.
Never heat a closed container if there is no means of pressure
relief.
iv.
Many substances, especially glass, remain hot for a long time
after they are removed from the heat source. Always check objects by bringing
the back of the hand near them before attempting to pick them up without
tongs, hot pads, or gloves.
v.
Never set hot glassware on cold surfaces or in any other way change its temperature suddenly, because uneven
contraction may cause breakage. •See
Chapter VI, Safe Handling of Equipment, for additional information on
heating, gas burners, and glassware. b. Steam. Live steam is
generated in experiments to determine coefficients of thermal expansion and
the heat of vaporization of water. Potential hazards can be avoided by
following a few simple guidelines.
i.
Produce steam only in a container with a direct open line to
the atmosphere.
ii.
Instruct students that steam has a very high heat capacity and
is invisible (the visible "vapor" is already condensed droplets).
Caution them not to aim steam outlets at their own skin or at other students.
iii.
Production of steam under pressures higher than atmospheric
pressure should be limited to teacher demonstrations. The teacher should take
necessary precautions associated with the higher temperatures of this steam
and the explosion hazards. c. Thermometers. Thermometers
present several possible hazards in the laboratory related to breakage and
spillage of mercury. Following the guidelines below will minimize the
hazards.
i.
Use alcohol thermometers in place of mercury thermometers to
eliminate the hazards associated with mercury spills.
ii.
Consider the range of temperatures to be measured when
choosing a thermometer. If heated beyond its capacity, a thermometer may
break.
iii.
Mount a thermometer in a safety rubber stopper whenever
possible. When using other types of stoppers, use a lubricant on the glass or
a split stopper. If necessary to free the thermometer from the stopper, split
the stopper with a single-edge razor blade. Teachers should ensure that
students use the thermometer in such a way that the equipment does not become
unstable.
iv.
If a mercury thermometer is used, be alert to the potentially
serious hazard of a mercury spill. Instruct students that they must report
any such breakage immediately and remove any source of heat which is present.
Each laboratory where mercury is used should be equipped with a mercury-spill
kit. Follow the directions that come with the kits. See Chapter VI.C, Thermometers, for
guidelines on using thermometers. d. Burns. A common cause
of student injury is a burn from recently heated glassware. To avoid such
burns, check the glassware by bringing the back of the hand close before attempting
to pick it up. In case of an accidental burn, administer first aid and visit
the appropriate health care person in the school. e. Asbestos. Many older hot
plates, hair dryers and other heating elements contain wires or parts insulated
with asbestos. Since the dangers of asbestos are well documented, all efforts
should be made to replace this equipment with non-asbestos-insulated
apparatus. 2. Cryogenics Dry ice (solid
carbon dioxide) is used in some low-friction pucks, as a source of carbon
dioxide gas, and as a cooling agent. A mixture of dry ice and alcohol or
liquid nitrogen might also be used as low-temperature baths. The temperatures
of these materials are low enough to cause tissue damage from a cryogenic
"burn." This is not likely to occur if contact is brief, because
the vapor layer formed between the cryogen and the tissue is not a good
conductor of heat. Follow the guidelines below to avoid a dry ice "burn." a. Flush the skin
that came into contact with the dry ice with water. Water should always be
readily available during cryogenic experiments. b. In preparing a
dry ice/alcohol mixture, pour the alcohol over the dry ice rather than
dropping the dry ice into the alcohol to avoid spattering. When storing
alcohol that has been used in a dry ice/alcohol mixture, the alcohol should
be returned to room temperature to allow the escape of excess dissolved gas
before placing in a closed container. c. When dry ice is
used in a confined space, provide sufficient ventilation to eliminate the
risk of asphyxiation. This risk is caused when the more dense carbon dioxide
gas released produces an oxygen-deficient layer. d. Used to produce a
special effect (such as fog in a drama production), dry ice may produce large
amounts of carbon dioxide. Students and other teachers should be warned of
this risk and informed about avoiding it. e. Cryogens should
be kept in double-walled containers such as Thermos bottles or Dewars. Any
fluid which gets between the walls at low temperatures may become trapped and
vaporize at higher temperatures, building up pressure and exploding the
container. The outer wall should be heavily wrapped to avoid this hazard. E. Chemical Hazards in Physics 1. Carbon Dioxide The use
of dry ice in cryogenic experiments must be accompanied by precautions
against production of an oxygen-deficient atmosphere. Carbon dioxide, which
is more dense than air, easily collects in a
non-ventilated area. •See
Chapter XI.D.2, Cryogenics. 2. Carbon Monoxide Do not
allow carbon monoxide from incomplete combustion to collect in a closed area.
Always conduct demonstrations using small internal combustion engines under a
vented hood or outdoors. 3. Explosives Do not
attempt to make explosive compounds such as those that might be used in model
rocketry. Only factory-made, pre-loaded rocket engines should be used for
this purpose. 4. Flammables Do not
use flammable substances near an open flame unless the purpose is to
demonstrate flammability. Many flammables produce toxic fumes and should be
burned only under a vented hood. Large containers of flammable liquids should
be opened, and liquids transferred, in a room free from open flames or
electrical arcs and, preferably, under a fume hood. •See
Chapter VII.A.4.b, Storage of Flammable and Combustible Liquids, and Chapter
VII.B, Handling Reagent Chemicals. 5. Mercury Do not
use mercury in the classroom. Use alternate equipment not requiring mercury
in place of mercury. There are many reasons for this recommendation: The
vapors from free mercury are cumulatively toxic. Mercury is absorbed through
the skin. The vapors it forms are absorbed by inhalation. Complete clean up
of any mercury spill, which is absolutely necessary, is difficult to
accomplish. NOTE: As stated earlier, each laboratory where mercury is
used should be equipped with a mercury-spill kit. Follow the directions that
come with these commercially available kits. 6. Other Heavy
Metals/Solder Highly toxic
cadmium oxide may be produced when silver solder containing cadmium is
overheated. Some solders contain flux, which may produce noxious fumes. Use
fume hoods when working with these materials. 1. Infrared
Radiation Caution
students that, beyond a limited exposure, infrared waves (heat waves)
entering the eye can cause burns to the cells of the retina. Infrared lamps
and the sun are concentrated sources of these waves. a. Follow
manufacturer’s instructions when using any infrared lamp. b. The sun should
never be viewed directly, especially at times when its visible light is
partially obscured. (The visible light triggers the body’s natural defenses
of avoidance and pupil constriction.) Lenses and sunglasses do not offer
protection from this radiation. Safe viewing of the sun can be done by
projecting an image of it through a very small hole onto a white piece of
paper about one-half meter behind the hole. 2. Microwaves A
microwave apparatus is often used to demonstrate various wave behaviors of
electromagnetic radiation. Microwave devices designed for high school use
have sufficiently low power to be free of radiation hazards when the
manufacturer’s instructions are followed. Microwave ovens that are in good
working order and used properly do not pose any safety hazard in a classroom.
Follow these guidelines: a. Check the
apparatus for radiation leakage before use if there are any doubts about its
safety. b. Inspect ovens
periodically to ensure they are clean and the door, hinges, vision screen, seals,
and locks are secure and working properly. c. Do not place
metal objects in the heating cavity. d. Do not permit
students to stand close to an oven during operation. 3. Radioisotopes Radioisotopes
produce biological injury (cell damage) resulting from their ionizing
properties. Gamma rays and beta particles are hazardous both inside and
outside the body. Alpha particles cannot penetrate skin and are not hazardous
if kept outside the body. The use of license-exempt quantities especially
sealed sources will create minimum hazard because of the small amount of
radiation present. Safe handling requires these protective measures: a. Time. Minimize
contact time with samples. b. Distance. Use tongs,
forceps, etc., to avoid direct contact. c. Shielding. Use shielding
appropriate for the radiations encountered. d. Storage. Store
radioactive materials so that people are not in frequent close proximity to
them and they are not damaged accidentally. 4. Ultraviolet
Radiation Ultraviolet
light can be absorbed in the outer layers of the eye, producing an
inflammation known as conjunctivitis. The effect usually appears several
hours after exposure and, unless the exposure is severe, will disappear
within several days. Sources of harmful ultraviolet light likely to be
encountered in physics include mercury vapor lamps, electrical arcs (e.g.,
the carbon arc lamp), incandescent ultraviolet lamps, and the sun. a. Mercury vapor
lamps and electric arcs should not be observed without elimination of their
ultraviolet emissions. b. Plastic or glass
sheets which transmit poorly in the ultraviolet region offer good protection
for the viewer of these sources. c. Use black paper
with caution because, while it absorbs well in the visible range, it may be
highly reflective in the ultraviolet range. d. The sun should
never be observed directly. •See
Chapter XI.F.1., Infrared Radiation. e. Incandescent
ultraviolet lamps present a minimal danger from their ultraviolet emissions,
as the energy of this radiation is very low. These bulbs, however, get
extremely hot when in use and must be given plenty of time to cool before
handling. 5. Visible Light
(including Lasers) Intense
sources of visible light are usually not hazardous due to the inability of
the human eye to remain focused on an intense source. Infrared and
ultraviolet radiation sometimes present along with visible light provides a
greater hazard. •See
Chapter XI.G, Laser Safety. 6. X-ray Radiation X-rays
may be produced in any situation in which high-speed electrons strike a
target. These conditions may exist in evacuated tubes where the accelerating
voltages are in the range of 10,000 volts or more. Crookes tubes and other
cold cathode discharge tubes are potential sources of X-rays in the
classroom. (Spectrum tubes used to observe spectra of elements and compounds
are not a source of X-rays if the tubes are in good condition because the
enclosed gases prevent electrons from achieving high enough energies.) To minimize possible X-ray exposure, three
rules should be observed by teachers and students: a. Minimize the
voltages used to operate vacuum tubes. b. Maximize the
distance between the tube and the observers. c. Minimize the time
during which the tube is operated. If any tube or apparatus is suspected of emitting
X-rays, it should be checked for dangerous amounts of radiation. Commercial
companies listed in the yellow pages should be able to provide this service. The laser produces an intense,
highly directional beam of light that, if directed, reflected, or focused
upon an object, is partially absorbed, raising the temperature of the surface
and/or the interior of the object. Potentially, this can cause an alteration
or deformation of the material. These properties can cause adverse biological
effects in tissue. Photochemical effects are also a danger when the
wavelength of the laser radiation is sufficiently short (i.e., in the
ultraviolet or blue light region of the spectrum). Low-power lasers may emit
levels of light that are not a hazard, or are no more hazardous than an
electric light bulb. Some lasers concentrate visible
light to an extent that retinal damage can occur in a very short time.
Fortunately, these lasers are not often found in secondary school science
laboratories. Most lasers used in secondary school laboratories are the
continuous wave, low power (0.5 - 3.0 mW.), helium-neon lasers. The only
optical danger is possible damage to the retina if a subject looks directly
into the beam or non-diffused reflection. The diameter of the beam, the time
of exposure, blink response time, and retina spot size all can affect the
probability of injury. Since some of these lasers in this range are
considered Class III lasers (see chart below), certain safety precautions are
important to teach and use when working with lasers. •See Chapter XI.G.3, Laser
Guidelines. 1. Biological
Effects The
human body is vulnerable to the outputs of some lasers and can, under certain
circumstances, incur damage to the eye and skin. The human eye is almost always
more vulnerable to injury than human skin. In the near-ultraviolet region and
in the near-infrared region at certain wavelengths, the lens of the eye may
be vulnerable to injury. Of
greatest concern, however, is laser exposure in the retinal hazard region of
the optical spectrum approximately 400 nm (violet light) to 1400 nm
(near-infrared). Within this special region, collimated laser rays focus in a
very tiny spot on the retina. This hazard only exists if the eye is focused
at a distance; reflecting the laser light off diffuse surfaces also prevents
the hazard. Higher levels of laser radiation would be necessary to cause
injury. Since
this ocular focusing effect does not apply to the skin, the skin is far less
vulnerable to injury from these wavelengths. The light entering the eye from
a collimated beam in the retinal hazard region is concentrated by a factor of
100,000 times when it strikes the retina. 2. Safety Standards A system
of laser hazard categories has been developed based on millions of hours of
laboratory and industry laser use. Each laser is placed into one of at least
four separate classes, or risk categories. The safety measures to reduce or
eliminate accidents depend upon which class of laser is being used. See the
chart below for laser risk classes and their hazards. Laser Risk
Classes*
* Adapted from Fundamentals of
Laboratory Safety 3. Laser Guidelines Lasers
can be used safely through the use of suitable facilities, equipment, and
well-trained personnel. Class II lasers require no special safety measures. However,
as in the case of a movie projector, a person should not stare directly into
the projection beam. Safety training is desirable for those working with
Class III systems. Eyewear may be necessary if intrabeam viewing cannot be
precluded. Operation within a marked, controlled area is also recommended.
Finally, for Class IV lasers or laser systems, eye protectors are almost
always required; facility interlocks and further safeguards provide
additional protection. The
following general guidelines for safe laser use in the classroom are
excerpted from Laser Fundamentals and Experiments. a. Before operation,
warn all individuals present of the potential hazard. b. In conspicuous
locations inside and outside the work area and on doors giving access to the
area, place hazardous warning signs indicating that a laser is in operation
and may be hazardous. c. Do not at any
time look into the primary beam of a laser. d. Do not aim the
laser with the eye. Direct reflection can cause eye damage. e. Do not look at
reflections of the beam. These, too, can cause retinal burns. f. Do not use
sunglasses to protect the eyes. If laser safety goggles are used, be certain
they are designed for use with the laser being used. g. Report any
afterimage to a doctor, preferably an ophthalmologist who has had experience
with retinal burns. Retinal damage is possible. h. Do not leave a
laser unattended. i. View holograms
only with a diverged laser beam. Be sure the diverging lens is firmly
attached to the laser. j. Remove all
watches and rings before changing or altering the experimental setup. Shiny
jewelry can cause hazardous reflections. k. Practice good
housekeeping in the lab to ensure that no device, tool, or other reflective
material is left in the path of the beam. l. Before a laser
operation, prepare a detailed operating procedure outlining operation. m. Whenever a laser
is operated outside the visible range (such as a CO2 laser), a
warning device must be installed to indicate its operation. n. A key switch to
lock the high voltage supply should be installed. o. Use the laser
away from areas where the uninformed and curious might be attracted by its
operation. p. Illuminate the
area as brightly as possible to constrict the pupils of the observers. q. Set up the laser
so that the beam path is not at normal eye level (i.e., so it is below 3 feet
or above 6˝ feet. r. Use shields to
prevent strong reflections and the direct beam from going beyond the area
needed for the demonstration or experiments. s. The target of the
beam should be a diffuse material capable of absorbing the beam and
reflection t. Cover all exposed
wiring and glass on the laser with a shield to prevent shock and contain any
explosions of the laser materials. Be sure all non-energized parts of the
equipment are grounded. 1. Local Regulations Before beginning
a model rocket program, check local school system regulations on the use of
model rockets. Be sure also to check regulations about launch sites and fire
codes in your area. •See
NFPA 1122. The
following website offers more information on this topic: 2. Model Rocketry
Safety Code Follow
the guidelines for safe launching and recovery of model rockets outlined
below. a. Construction. In making model
rockets, use only lightweight materials such as paper, wood, plastic, and
rubber; use no metal as structural parts. b. Engines. Use only
pre-loaded, factory-made model rocket engines in the manner recommended by
the manufacturer. Do not alter or attempt to reload the engines. c. Flying
Conditions. Do not launch a rocket in high winds or near buildings, power
lines, tall trees, low flying aircraft, or under any conditions that might
endanger people or property, such as the threat of lightning. d. Jet Deflector. The launcher must
have a jet deflector device to prevent the engine exhaust from hitting the
ground directly. e. Launch Area. Always launch
rockets from a cleared area that is free of any easy-to-burn materials; use
non-flammable recovery wadding. f. Launch Rod. To prevent
accidental eye injury, always place the launcher so the end of the rod is
above eye level, or cap the end of the rod with the hand when approaching it.
Never place head or body over the launching rod. When the launcher is not in
use, always store it so that the launch rod is not in an upright position. g. Launch Safety. Do not let anyone
approach a model rocket on a launcher until making sure that either the
safety interlock key has been removed or the battery has been disconnected
from the launcher. h. Launch Targets
and Angle. Do not launch a rocket so its flight path will carry it
against a target on the ground; never use an explosive warhead nor a payload
that is intended to be flammable. The launching device must always be pointed
within 30 degrees of vertical. i. Launching System. The system used
to launch model rockets must be remotely controlled and electrically
operated, and must contain a switch that will return to "off" when
released. All persons should remain at least 10 feet rom any rocket that is
being launched. j. Power Lines. Never attempt to
recover a rocket from a power line or other dangerous places. k. Pre-Launch Test. When conducting
research activities with unproven designs or methods, try to determine their
reliability through pre-launch tests. Conduct launching of unproven designs
in complete isolation from persons not participating in the actual launching.
l. Recovery. Always use a
rocket system with model rockets that will return them safely to the ground
so that they may be flown again. m. Stability. Check the
stability of model rockets before their first flight, except when launching
models of proven stability. n. Weight Limits Model rockets
must weigh no more than 453 grams (16 ozs.) at liftoff,
and the engine must contain no more than 113 grams (4 ozs.) of propellant. For further information about model rockets and model
rocket safety, contact: Estes Rocket
Industries
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