School Science Lessons
(UNPh07)
2024-11-29
Laboratory safety
Contents
7.1.0 Safety in the school laboratory
7.2.0 Laser safety
7.3.0 Radiation safety
7.1.0 Safety in the school laboratory
7.1.1 Teacher rules
7.1.2 Laboratory rules
7.1.3 Experiments rules
7.1.4 Equipment rules
7.1.5 Operation rules
7.1.6 Radioactive substances
7.2.0 Laser safety
7.2.1 Laser safety
7.2.2 Class 1 lasers
7.2.3 Class 2 lasers
7.2.4 Screens or shields
7.2.5 Warning signs.
7.3.0 Radiation hazards
7.3.1 Radiation hazards
7.3.2 Radiation exposure
7.3.3 Radiation dose from radioactive materials entering the body
7.3.4 Shielding
7.3.5 Radioactive decay of Bismuth-214
7.3.6 Radioactive sources
7.3.7 Radiopharmaceuticals, Technetium 99m
7.3.8 Cold cathode tubes, discharge tubes, safety regulations.
7.1.1 Teacher rules
Ensuring the safety of the students in various activities and experiments is the most basically responsibility of the teacher.
Remember that the students not only lack safety consciousness, but also can be so fascinated by those interesting things that they forget safety problems.
Any activity (even a walk or having a bath) can be dangerous, but this should not stop you organizing the students to take part in the experiments and activities simply, because of the danger.
The best way is to tell the students the specific method of avoiding danger.
It is necessary to master some techniques for those experiments where the danger is too high for the experiment to be done by the students themselves.
When these experiments are done, they should be shown by the teacher and the students reminded only to observe and not to touch.
All such experiments should be done by trained teachers in advance, to find where danger exists and to see if the students can do the experiment themselves and to find out specific methods to avoid danger.
7.1.2 Laboratory rules
1. The school laboratory should have two doors, a front door and a back door.
The passage way in front of the doors should be always clear.
There should not be any obstacles in laboratory passages or on the floor or in any space where students operate.
2. Fire extinguishing materials, e.g. fire blanket or carpet, sand bucket, and fire extinguisher should be permanently installed in each laboratory.
3. The school laboratory should also have first aid materials and electrical fuses or circuit breakers.
Earth leakage protection units should be installed in the electrical supplies.
4. A special vessel should be used to collect broken pieces of glass.
Do not place the broken glass into he garbage can.
Before use by students, all glass containers and tubes should be checked for any cracks or liquid leakage.
The open ends of glass tubes should be flame-polished into a smooth shape.
5. At regular intervals inspect any high voltage, i.e. mains voltage, apparatus and check if the wires have been exposed or plugs damaged.
The inspection should be done by a person qualified in electrical installation and repair.
6. Mercury and radioactive sources must operated in a fixed place with suitable protection equipment and procedures according to regulations and laws of Government and school authorities.
7.1.3 Experiments rules
1. Never do experiments that are dangerous for others or yourself, except as permitted by school authorities.
If you are not sure if the experiment is dangerous or not, or beyond your knowledge, ask an experienced teacher before doing it.
2. Do not turn on the equipment that you have never used.
3. Do not operate equipment before reading the booklet of directions.
4. Do not use materials which are easily burned where fire exists.
5. Learn the positions of the fire extinguisher, electric switch and first aid dressing in a new experimental environment or laboratory.
6. Learn how to use them in the case of emergency, and master the correct method of temporary treatment of a wound.
7.1.4 Equipment rules
1. Always use safety glasses and thick gloves when you process something that can easily burst apart, rebound or spurt.
2. Do not touch the object that is moving or spinning in high speed.
3. Do not touch along the edge of a knife or the edge of a piece of glass that is not rubbed smoothly.
4. Do not clean the pieces of the glass by your hands directly.
5. The electricity above 30 volts may be dangerous.
The edge of screw mouth of lamp holder may be wrongly connected as a live wire.
6. When you doing the measurement outside, do not work under the high voltage power transmission line.
7. A working lamp above 10 watt and the metal just heated can burn the hands so wear a pair of gloves.
8. The laser, arc light, electric welding, X-rays and ultraviolet rays should not get into the eyes.
Do not look directly at a laser tube even if it is not turned on.
Do not remain exposed to ultraviolet light and X-rays.
X-rays should not be used in schools!
7.1.5 Operation rules
1. Observe the surroundings around you before each experiment to avoid unnecessary hurt to others, yourself and the equipment and facilities.
2. Do not touch the equipment without the permission of the teacher at any time.
3. Remember unexpected hazards or dangers can happen, even with normal working.
Operate equipment according to the instruction booklet or teacher's directions.
Follow the normal method of using tools.
4. While using tools only place your hands on the operating handles and ensure your assistants have their hands in safe positions.
Make sure that no hands are near a cutting or hot surface.
5. Do not allow tools to fall from the working table.
This can damage the tool or hurt your feet or the feet of your assistants.
6. Do not turn on any circuit which has not been checked.
First use the method of turning on instantaneously (turn on, then turn off immediately).
Note to observe if the direction of the pointers on any meters is correct and the measuring scale is suitable.
After everything is checked to be correct, you again turn on the circuit.
7. Turn off the main source when you find the wire or coil being over hot, a rubber washer becoming soft, the burnt smell or overflow of the substance that is easily burnt and hear the sound of mechanical rubbing, which is not normal.
Do not turn the circuit back on before finding the reason for the problem and fixing the problem.
8. Do not examine and repair any equipment or find circuit problems while the circuit is operating at a high voltage, e.g. the main power supplies.
If you use an electric pen with a neon tube, make sure the pen is working before using it to find the fault in a circuit or to check for live wires.
9. After each experiment turn off the electric power and gas source then return the equipment and tools to their original positions.
The accessories of the meters should be placed in the same storage position as the meters.
10. Any damaged equipment, even a broken wire, should be reported to the teacher.
11. The last person to leave the laboratory should turn off the main source of electricity and gas.
7.1.6 Radioactive substances
1. Sources of radioactivity must be put in a container made of lead with an eye catching mark outside of the container.
The international radiation symbol is recommended.
2. Use the source of radioactivity in a special room.
The persons who uses the source of radioactivity should sign their name and time when they enter and leave the room.
Use tweezers or tongs and wear gloves when using the source of radioactivity and wash hands thoroughly when leaving the source of radioactivity.
3. The following information has been extracted from the Code of Practice for the Safe Use of Ionizing Radiation in Secondary Schools (1986) and the Code of Practice for the Safe Use of Lasers in Secondary Schools (1995), produced by the National Health and Medical Research Council:
3.1 Radioactive substances generally emit α or β particles or γ rays or combinations of these, while X-ray units generate electromagnetic waves, similar to γ rays, but usually of lower frequency (and longer wavelength).
3.2 The amount and type of shielding needed depends on the penetrating power of the particular form of radiation.
The denser the shielding material the better shield it will be.
The α particles, being charged and relatively heavy atomic particles, are easily stopped, while γ rays, usually being very short waves, are far more penetrating and hard to stop.
α-particles: Stopped by sheet of paper or surface layers of skin.
β-particles: Stopped by a few millimetres of aluminium or 1-2 centimetres of plastic.
γ-rays: Almost completely stopped by about 1 metre of concrete or about 5 centimetres of lead.
Most will pass through the human body.
X-rays (medical): Almost completely stopped by 2-3 millimetres of lead, or about 10-15 centimetres of concrete.
Will pass through the body with some absorption depending on the density of organs in the beam (e.g. skin, bones).
4. The philosophy for the control of hazards associated with the use of ionizing radiation is as follows:
* No practice should be adopted unless its introduction is necessary and produces a positive net benefit, and,
* all exposure should be kept as low as possible.
5. Ionizing radiation in schools must only be used in simple experiments to show fundamental principles.
The sources used and the methods of using them must be chosen to ensure that the degree of hazard is negligible.
Consideration should be given to minimizing the number of experiments or demonstrations that may take place in a year.
6. Advice in planning such experiments or demonstrations should be sought from: Division of Health and Medical Physics, Queensland Health
Department 535 Wickham Terrace Brisbane Q 4000, Australia.
Advice for packaging, transportation and disposal of radioactive substances should be sought from: Radiation Health 450 Gregory Terrace,
Fortitude Valley Q 4006, Australia.
7. The immediate responsibility for radiation safety in any experiment involving radiation rests with the teacher responsible for the class.
No demonstrations or experiments requiring the exposure of students, staff or any other person to ionizing radiation shall be done.
8. Physics Discussions
A purchased radiation sample or natural source must still be managed in the same way.
The prepared samples are probably easier and safer, because they are known quantities and sealed in resin.
Managing a radiation sample storage and testing requires of understanding what is required.
A Radiation Officer must be appointed by the school the school Principal.
Natural ores and mounted sources are placed inside a thick lead container which is placed inside a pad-locked toolbox which is placed inside the school safe.
A register of use and only the Head of Science Department may take them out and return them.
There is zero chance of receiving a medically significant dose under normal circumstances.
The only risk would be swallowing the sources.
Losing any sources would be a big reporting problem so make sure processes are in place where a source cannot be lost.
Detectable radiation occurs everywhere: Besser type bricks, smoke detectors, non-stick frypans (containing PTFE) are particularly active.
It is difficult to not get any radiation in an experiment, because when apparatus is set it up on the bench with no sources and background radiatin events will be detected.
The commercial "School Radioactive Sources” (TM), provide alpha, beta and gamma, but they are so expensive, (AUD $295 each).
They last a long time, but the "Co-60" has a half life of about 6 years and is useless after 5 half-lives.
The "alpha emitter Am-241", which had a half life of hundreds of years, has been changed to "Po-210", with a half-life less than a year.
A syllabus may include has two pracs on radioactivity: intensity and distance, and shielding effects.
Teachers who do not want to buy sources, because of the cost or the safety hazards, can substitute visible light for the source in both cases.
For the intensity and distance experiments, use a darkened room, a light source (raybox kit) and a light sensor (e.g. Vernier)
A inverse square relationship with distance similar to that of nuclear radiation can be obtained.
For shielding effects, use a light source and a light meter separated by about 10 cm.
Use pieces cut out of the side of a 2L milk container as the shields.
Use about 7 layers to cut the intensity in half (the HVL or half-value layer) and that was similar to alfoil and Sr-90 beta radiation.
A graph can be linearized by taking the natural log of the intensity.
7.2.1 Laser safety
1. Lasers can burn tissue in the eye, because the lens of the eye may concentrate the laser beam to a very small image on the retina.
High power lasers may damage the skin.
Lasers are classified according to the degree of hazard that depends on the output power, the size of the beam, the irradiance at any point in the beam, the wavelength, and the power in a single pulse and the repetition frequency, if it is a pulsed laser.
All lasers and laser products must bear a label stating the class of the laser product, the wavelength emitted or the medium, and maximum power output.
2. Class 1 lasers cannot cause harm, because the exposure level that produces injury cannot be reached under any conditions.
Class 2 lasers are low power devices that emit visible radiation.
Blinking should protect the eyes from them.
Classes 3A, 3B and 4 lasers are not permitted in schools.
3. The teacher should warn students that they should never shine a laser beam directly into a person's eyes.
Some irresponsible people have direct laser beams at the drivers of moving vehicles and the pilots landing aeroplanes.
4. Sunglasses and welder's goggles do not provide protection from laser beams.
Use approved shields to prevent both strong reflections and the direct beam from going beyond the area needed for the experiment.
Paint the shields matt black to reduce reflection.
Reflection of laser beams may occur from polished metal trimmings on instrument housings and from mirrors, bottles, glass lenses, watches, rings, cufflinks, polished wooden furniture, windows or any smooth surface.
Fix the laser head rigidly in position so that the direction of the laser beam cannot be accidentally altered.
The room lighting in the laser work area should be as bright as possible to constrict the pupil diameter of the observer's eyes.
5. Do not use a laser in a dark room.
The direct contact of eyes and the laser beam is forbidden.
Be careful to note if the laser can hit on a smooth surface before turning on the laser, because the reflected laser can enter other's eyes.
For the same reason, do not move laser equipment when it is working.
Instructions for Australian Teachers:
6. The hazard from lasers is primarily that of burning of tissue either in the eye or, for high power lasers, the skin.
The eye is particularly at risk, because the lens of the eye may concentrate the beam to a very small image on the retina, in which the energy density is extremely high.
Lasers are classified according to the degree of hazard presented.
This depends on the output power, the size of the beam, the irradiance at any point in the beam, the wavelength, and for a pulsed laser, the power in a single pulse and the repetition frequency.
All lasers and products incorporating lasers must bear a label stating the class of the laser product, the wavelength emitted or the medium, and maximum power output.
Devices above Class 1 must have additional safety markings.
Class 1 lasers are intrinsically safe, i.e. they cannot cause harm, either, because the exposure level that produces injury cannot be reached under any conditions, or, because engineering design is such that access to dangerous levels is not possible.
Class 2 lasers are low power devices that emit visible radiation.
They are not intrinsically safe, although eye protection is normally afforded by aversion responses (e.g. blinking).
Classes 3A, 3B and 4 are not permitted in schools.
The supervision of the use of lasers throughout a school shall be the responsibility of the head of department / principal.
This person shall be responsible for the buying, storage and allocation of lasers, and for ensuring that the needs of the code are met at all times.
Only Class 1 or Class 2 lasers should be used in schools.
7. The safe use of lasers for all applications is controlled by Australian Standard AS 2211.
This document follows international standards, sets classifications of lasers, and documents some of the safe practices for general applications.
Guidelines for the safe use of lasers in the classroom have been developed by the National Health and Medical Research Council of Australia
(NH and MRC) in a Code of Practice for the safe use of Lasers in Secondary Schools (1983).
Copies of this code and further advice should be obtained from:
The Director Division of Health and Medical Physics Department of Health 450 Gregory Terrace Brisbane Q 4000.
7.2.2 Class 1 lasers
Class 1 lasers require no special safety precautions other than to warn students that good practice dictates that you never shine a laser beam, regardless of its class, directly into someone's eyes.
7.2.3 Class 2 lasers
Responsibility
1. Lasers must only be used under the direct supervision of a member of the science staff and should be used for demonstration purposes only.
2. The teacher of science in charge of a demonstration shall be immediately responsible for the safety of that demonstration and the teacher shall ensure that risk assessment and management are implemented.
3. If a new demonstration is to be introduced, then a trial must be done, without students present, to evaluate the safety aspects of the demonstration.
4. All persons must be instructed not to look directly into the main beam or reflected or refracted beams and students must be warned of the potential hazard and the seriousness of eye damage.
5. Access to laser work areas should be limited and casual observers should be excluded.
7.2.4 Screens or shields
1. Sunglasses and welder's goggles do not provide protection from laser beams
Provided appropriate shields (i.e. shields complying with the code) are used, it is not necessary for teachers or students to wear additional protective eye wear.
2. Shields must be used to prevent both strong reflections and the direct beam from going beyond the area needed for demonstration.
Shields must be painted matt black to reduce reflection.
The base material of such shields must not have a shiny surface as paint may flake exposing a mirror like surface.
3. Specularly reflected beams from shiny objects may be hazardous even when only a small amount of the incidental beam is reflected.
Such reflections may arise from polished metal trimmings on instrument housings and from mirrors, bottles, glass lenses, watches, rings, cufflinks, polished wooden furniture, windows or any smooth surface.
These articles should be removed from the vicinity of the laser or covered with matt black paper or cloth.
Care must be taken to ensure that surfaces that would otherwise reflect diffusely do not become wet as this may cause specular reflection.
4. Baffles should be placed near lenses in the beam path, to intercept oblique specularly reflected beams and oblique refracted beams.
5. The laser head must be rigidly fixed in position so that the direction of the laser beam cannot be accidentally altered.
Optical components and shields must also be firmly fixed in position.
6. The room lighting in the laser work area should be as bright as practicable while the laser is in operation, to constrict the pupil diameter of the observer's eyes.
7.2.5 WARNING SIGNS
Each Class 2 laser must have attached to it a warning label with the following dimensions: background, yellow, lettering, black, 10.5 cm × 5.2 cm, and wording.
DANGER LASER
DO NOT LOOK INTO DIRECT OR REFLECTED BEAMS
When a Class 2 laser is in operation, warning signs must be displayed in conspicuous locations both inside and outside the demonstration area.
These signs must be removed when the laser is not in use.
Area warning signs must conform to the following dimensions, wording and design.
Colour scheme: background, yellow, lettering, black.
Minimum dimensions: 20 cm edge triangle:
DANGER LASER
LASER OPERATING IN THIS AREA.
7.3.1 Radiation hazards
1. Radioactive substances usually emit α particles or rays or combinations of these X-ray units generate electromagnetic waves similar to γ-rays, but usually of lower frequency and longer wavelength.
The amount and type of shielding needed depend on the penetrating power of the particular form of radiation.
Sources of radiation are limited to sealed sources, radioactive chemical and mineral samples and high voltage electrical equipment.
The α- particles are charged and relatively heavy atomic particles, so are easily stopped by a sheet of paper or the surface of the skin.
β-particles are stopped by a few millimetres thickness of aluminium or 2 cm of plastic material.
γ-rays have very short wavelength and are more penetrating and harder to stop.
They are almost completely stopped by about 1 metre of concrete or about 5 cm of lead.
Most will pass through the human body.
Medical X-rays are almost completely stopped by 3 millimetres of lead or 15 centimetres of concrete.
X-rays pass through the body with some absorption depending on the density of organs, e.g. skin, bones.
2. Only teachers or laboratory staff are allowed to handle radioactive sources.
Ionizing radiation in schools must only be used in simple experiments to demonstrate fundamental principles.
The sources used and the methods of using them must be chosen to ensure that the degree of hazard is negligible.
In school experiments involving X-rays or radioactive substances the radiation levels should be so low that no special shielding is required.
However, it is important when using sources of radiation in schools to demonstrate the role of shielding as part of safe working practices.
All radiation sources must be stored in separate lockable metal containers, e.g. a metal cash box, which are permanently labelled and kept in the school safe with access to authorized members of the school staff.
Geological sample containing radioactive materials must be securely stored.
Only minute amounts of radioactive materials are allowed to be kept in schools for demonstration purposes.
The quantity of radiation absorbed by people during the short time they handle the equipment is negligible compared to the natural radiation.
Never open a radioactive source or try to dissolve it in acid or other solvent.
Radioactive sources at the end of their useful life must be disposed of according to government regulations.
3. Cold cathode discharge tubes may include a discharge tube with side tube for connection to a vacuum pump, Maltese cross
discharge tube to illustrate the deflection of cathode rays by magnetic fields, windmill tube.
These tubes are operated by high voltages produced by induction coils and may produce unwanted X-rays if operated at too high a voltage.
Use the lowest voltage from the induction coil changing the distance of the make-and-break hammer from the iron core of the induction coil windings.
Start with the hammer away from the core and use the adjusting screw to slowly decrease the distance between them until the discharge tube operates.
Only teachers should operate a discharge tube, for a short a time as possible and with both teacher and student at a minimum distance of one metre from it.
7.3.2 Radiation exposure
The possible modes of radiation exposure can be divided into two types: external or internal exposure.
External irradiation results from the exposure to X-rays or to radiation from sealed or unsealed radioactive sources external to the body.
1. Radiation dose from X-rays
The radiation dose is dependent on the following:
* operating factors of the X-ray tube (kV (peak) and mA),
* duration of irradiation,
* protective barriers between the tube and the body,
* distance between the tube and the body,
* filtration of the X-rays by material in the beam,
* amount of scattering of the primary beam that has taken place.
2. Radiation dose from radioactive materials external to the body
The dose is dependent on the radionuclide and:
* the type of radiation emitted by the radioactive materials,
i.e. α particles, β particles, γ radiation or combinations of these, and the energy of the radiation emitted,
* the activity of the radioactive substance,
* the distance between the source and the body,
* the protective barrier between the source and the body, and
* the duration of exposure to the rays.
Shielding may be needed to protect staff and students.
7.3.3 Radiation dose from radioactive materials entering the body
Internal irradiation results from the entry of radioactive materials into the body, with the resultant exposure of organs that have absorbed such materials and, in most cases, the exposure of other nearby organs.
The amount of radioactive materials taken into the body depends many factors, including the following:
* the activity of the radioactive material being handled,
* its physical state, e.g. liquid, gas, powder, aerosol, solid,
* its concentration and chemical form,
* methods of handling and precautions taken,
* personal hygiene,
* the duration of handling, and,
* site of entry into body, e.g. skin, wound, mouth, nose.
The radiation dose resulting from the entry of a particular amount of radioactive material into the body depends on the following:
* the type of radioactive material,
* the type and energy of the radiation it emits,
* its solubility, physical and chemical form, and effective half life, and,
* the biological behaviour (or characteristics) of the radioactive material, e.g. some elements are selectively absorbed by certain organs of the body, such as iodine by the thyroid, and radium and strontium by bone.
7.3.4 Shielding
In school experiments involving X-rays or radioactive substances the radiation levels should be so low that no special shielding is required.
However, it is important when using sources of radiation in schools to show the role of shielding as part of safe working practices.
7.3.5 Radioactive decay of Bismuth-214
When Bismuth-214 decays by emitting an alpha particle, He2+,
214Bi --> 210 Tl + 4 He
The "daughter isotope" is Thalium-210.
7.3.6 Radioactive sources
The teacher of science must ensure that:
1. Only approved sealed radiation sources are used.
2. All radiation sources are stored in lockable metal containers (metal cash box is suitable) which are permanently labelled.
3. If there is more than one source, then they should be stored in separate compartments within the box.
4. This container should be kept in the school safe.
5. Access to this container is limited to authorized members of the school staff.
6. Sources are clearly labelled with the word "Radioactive", with the type and activity of the radionuclide and, for short half life (less than 10 years) material, the year of manufacture.
7. Ionizing radiation sources in schools are only used for simple experiments to show fundamental principles.
8. The sources used and the method of using them must ensure that the degree of hazard is negligible.
9. Gifts of radioactive sources, discharge tubes, operational high voltage generators or X-ray units of any kind are not accepted.
10. No demonstrations or experiments requiring the deliberate exposure of students, staff or any other person to ionizing radiation are done.
11. Routine checks of the condition of each source are done out at intervals not exceeding 5 years.
12. Checks must be done sooner following an event such as a fire or an accident that may have damaged the source.
13. If a source of radiation is lost, or suspected of being stolen or damaged, report the matter in the first instance to the principal, who shall then inform the Department of Education and the Division of Health and Medical Physics.
14. The immediate responsibility for radiation safety in any experiment rests with the teacher of science responsible for the class.
The teacher should ensure that:
15. radiation sources are only handled by tongs or forceps,
16. Radiation sources are used by students only when under direct supervision,
17. All sources of radiation are accounted for,
18. Radiation sources are clearly marked as radiation sources, and no person stands within one metre of operating equipment.
7.3.7 Radiopharmaceuticals, Technetium 99m
Diagnostic radiopharmaceuticals are used to study the way the body is functioning and identify if something is going wrong, e.g. Technetium 99m (Tc-99m) and Iodine-123 (I-123).
Therapeutic radiopharmaceuticals are used to kill cancer cells, which are sensitive to damage by radiation, e.g. Iodine-131 (I-131).
Technetium 99m is the most widely used radioisotope in nuclear medicine imaging.
Compared to other reactor-produced medical isotopes, technetium-99m is particularly useful, because the half-life of Tc-99m is 6.01 hours.
This is much shorter than the half-lives of other medical radioisotopes, e.g. Sm-153 (46.7 hours), Mo-99 (66 hours).
So Tc-99m will decay into stable isotopes quickly and will stop producing radiation after a day or two and the patient will not be exposed to
dangerous radiation for a long time.
7.3.8 Cold cathode tubes, discharge tubes, safety regulations
1. The following gas discharge tubes supplied to schools fall into this category:
1.1 Discharge tube with side tube for connection to a vacuum pump,
1.2 Maltese cross discharge tube,
1.3 Discharge tube to illustrate the deflection of cathode rays by magnetic fields,
1.4 Windmill tube
2. The following precautions must be taken when using any one of the tubes mentioned above:
2.1 The voltage applied should be kept as low as possible.
The voltage from the induction coil varies by changing the distance of the make-and-break hammer from the iron core of the induction coil windings.
Commence with the hammer well away from the core and slowly decrease the distance between them (by means of the adjusting screw) until the tube operates.
2.2 Such tubes shall be operated by the teacher of science for demonstration purposes only.
2.3 The use of these tubes should be limited to as short as time as possible.
2.4 All students should be kept a minimum distance of one metre and teachers should also try to observe this distance.
All these tubes are operated by high voltages produced by induction coils and may produce unwanted X-rays incidental to their intended use.
2.5 The voltages necessary to operate these tubes depend upon the dimensions of the tube and the pressure of the gas in the tube.
Generally, the higher the voltage used, the greater the danger of the production of unwanted X-rays.