Science Safety
Chapter 7b
Hazards
Corrosive Chemicals
Reactive Chemicals
Insidious Hazards
Toxic Hazards
Biological Hazards
Radiation Hazards
A toxic substance has the potential to injure by direct chemical action with body systems. Almost any substance is toxic when taken in excess of tolerable limits. Toxic substances include corrosive as well as poisonous materials.
Toxic materials can enter the body by
- inhalation breathing in poisonous or corrosive vapours and dust is the most common route by which toxic materials enter the body
- ingestion swallowing liquid or solid toxic materials
- direct entry to the blood stream chemicals entering through open wounds may travel throughout the body (direct injection through punctures can also occur)
- contact absorbing toxic materials through skin, mucous membrane, and eyes
The effects of corrosive materials are usually rapid, but the effects of poison may not be immediately noticed. Many substances' effects (e.g., arsenic and mercury) are cumulative and poisoning can be the result of several exposures over a period of time.
Poisoning may be suspected when any of the following are evident. They are
- strange odour on the breath
- unconsciousness, confusion, or sudden illness
- discoloration of lips and mouth
- pain or burning sensation in the throat
- drugs or poisonous chemicals in bottles or packages found open in the presence of students
Toxic materials damage the body by interfering with the function of cells in body tissue. Damage can occur when
- tissue is destroyed by direct corrosive action (e.g., NaOH contacts skin)
- toxic materials interfere with chemical reactions of the body (e.g., CO2 replaces O2 in hemoglobin)
- disruption of the biological processes occurs (e.g., NO2 causes pulmonary edema and allergic responses)
Toxic effects can be local or systemic as well as acute or chronic. Local effects are confined to the area of the body that has come in contact with toxic materials. Systemic effects occur throughout the body after absorption into the bloodstream. Acute effects are immediate, while chronic effects may take many years before they become evident.
Toxic materials or "controlled products" are rated in Manitoba by an Occupational Exposure Limit (OEL) as defined in sections 19 and 20 of the Workplace Health Hazard Regulation (53/88), a regulation under the Workplace Safety and Health Act (chapter W210).
The OEL is defined as the limit of exposure of a worker in a workplace to an airborne controlled product or an airborne ingredient in a controlled product.
- For most compounds, the OEL is the same as the threshold limit value (TLV) published by the American Conference of Governmental Industrial Hygienists (ACGIH).
- For designated compounds such as carcinogens, the OEL is as close to zero as practical and less than the TLV.
- An adjusted TLV may be determined and specified for mixtures or specific worker health issues.
- Substances with high rates of cutaneous absorption are labelled SKIN. The use of OEL is not appropriate because for these substances the danger is not the result of airborne exposure.
The potential for contact with toxic materials exists in activities suggested within various science curricula. Chemistry experiments are the most obvious situations with potential hazard. However, a person may be exposed to toxic substances from unsuspected sources. Toxic materials may be involved incidentally as part of a laboratory or demonstration procedure. Careful consideration must be given to all materials used and produced in an activity (e.g., the dust of heavy metal minerals may be inhaled during the breaking of rock samples).
Inadequate clean-up may lead to exposure to toxic materials after a lab procedure is finished. Substances left on benches or in beakers and bottles may expose others to these toxic materials. Students may ingest toxic materials they have been in contact with if they do not wash thoroughly before eating or smoking. Foods and beverages readily absorb many vapours and must never be brought into a lab. Chewing of gum should not be allowed.
Teaching About Toxic Hazards
Teachers should draw students' attention to procedures regarding toxic hazards at every opportunity.
Toxic Materials Protection Policy
Accident prevention depends on forethought, identification of hazards, and careful instruction. The onus is on the teacher to be aware of potential dangers and convey this information to students. The teacher must instruct students in proper handling procedures and must insist that they be followed.
The acquisition, use, and storage of toxic materials must be related to real needs. If safe alternatives exist, they should be used. Only minimum quantities should be stored. Stock bottles should not be allowed in the laboratory. Toxic materials should not be used unless there is adequate protection from exposure.
Suggested Lesson Plan:
Consider the time required and allow for frequent reinforcements of safety messages.
Placement:
Laboratory Safety Orientation (every science program)
Senior 1 Science Chemical Interactions
Senior 2 Science Laboratory Safety
The use of protective gear, prescribed handling procedures, and attention to absolute cleanliness must be the normal routine of any laboratory. Maintaining the routines requires safety attitudes that are nurtured by example and constant practice.
Students must be made aware of and obtain knowledge of the hazard presented by any substance they use. Appearance and odour will not always provide signals that indicate poisonous or corrosive substances are present. Most students are surprised by the wide range of dangers that exist when chemicals are incorrectly handled (see Student Handout: Toxic Materials below).
Student Handout: Toxic Materials
Hazardous situations include
- handling toxic materials in open containers vapours, dust, and liquids can easily escape during normal handling.
- heating toxic materials smoke and vapour may be released in much greater quantity when material is hot.
- creating dusts of toxic materials crushing and grinding solids, and transferring powders, may release dusts into the air.
- using toxic materials in areas without adequate ventilation toxic vapours can rapidly accumulate to dangerous levels in a room, or part of a room, that does not have a constant replacement of fresh air. Toxic vapours can be in high concentration immediately above an open bottle even in well-ventilated rooms - do not lean over the bottle.
- storing of toxic materials without proper ventilation dangerous levels of toxic substances accumulate in the air and on surfaces in closed, unventilated storage areas.
- storing toxic materials without proper hazard identification the hazards must be clearly seen and understood every time a substance is used in order to avoid dangerous mistakes.
- using toxic materials without proper protective gear skin contact with hazardous materials and inhalation of toxic vapours must be prevented by the use of correct clothing, face protection, fume hoods, or respirators.
- storing or consuming food and beverages, chewing gum, and smoking in an area where toxic materials are used food, beverages, and cigarettes can readily absorb toxic vapours or become contaminated with unseen toxic dust. Poisons may be transferred from hands to food and cigarettes.
Special Caution: Odours and appearance are not reliable guides to the toxicity of substances. What looks like water could be a dangerous acid or base -- or worse. Many toxic vapours have little or no odour, even in dangerous concentrations.
Protection
A variety of measures will provide protection. They include
- treating a substance as toxic unless you definitely know otherwise
- covering all exposed areas with chemical-resistant clothing when using poisonous or corrosive material (use appropriate protective gloves, aprons, lab coats, and face shields)
- washing with soap and warm water after handling any chemicals (hands and used glassware should always be clean at the end of a lab period)
- keeping food, beverages, and cigarettes out of all laboratory rooms
- never using lab glassware for eating or drinking
- working in a fume hood if using substances with toxic vapours or dusts
- labelling clearly all bottles (read the label so you know the hazard)
- replacing bottle lids as soon as you have taken the materials you need
- never storing any substance in an unlabelled container
- knowing the hazards and safe handling procedures of the substances you are working with (always know what to do in the event of an accident -- if unsure, ask the teacher to review emergency procedures)
Accident Procedures
In the event of an accident, students will
- alert the teacher speed is essential
- wash affected skin or eyes immediately (within 10 seconds), and continue for at least 15 minutes
- contact trained assistance immediately if a material has been inhaled or swallowed, or if a victim is unconscious, in convulsions, or in pain
Micro-organisms, like toxic chemicals, are a potential hazard to persons performing biological experiments. Working with them requires special handling, storage, and disposal techniques. Teachers must be aware of the hazards presented by infectious agents and their possible sources.
Occurrences of Accidental Infection
In approximately 80 per cent of all laboratory-acquired infections, the cause is unknown. In the remaining 20 per cent of the cases that have known causes, five are most frequent. They are
- oral aspiration through pipettes
- accidental syringe inoculation
- animal bites, scratches, or contact with an animal
- spray from syringes
- centrifuge accidents
Other common causes include
- allergic reactions to plants
- cuts or scratches from contaminated glassware
- cuts from dissecting instruments
- spilling or dropping cultures
- airborne contaminants entering the body through the respiratory tract
Precautions
- Pathogenic organisms should not be brought intentionally into a school laboratory.
- Do not encourage growth of any microorganisms other than those that occur naturally on mouldy bread, cheese, or mildewed objects. No attempt should be made to grow pure cultures of these organisms.
- Cultures should be grown at room temperature or in the range of 25°C to 32°C. Incubation at 37°C encourages growth of microorganisms that are capable of living in the human body.
- Food should not be stored in refrigerators in laboratories.
- Hands should be washed thoroughly after working with any cultures.
- All surfaces used should be washed down with an appropriate disinfectant (e.g., a solution of fresh bleach).
- All apparatus used in microbiology must be autoclaved. The oven of a kitchen stove may be used. Liquid disinfectants and germicidal agents generally have limited effectiveness and should not be relied upon for complete sterilization.
- Anaerobic bacteria should not be grown.
- Due to the possibility of culturing tetanus-causing organisms, bacteria from soils should not be grown.
- Cultures should not be grown of spores collected from telephones, door knobs, lavatories, etc. The body can routinely destroy small numbers of these bacteria, but may be overwhelmed by those produced in large numbers.
- At weekly intervals, shelves, cupboards, animal cages, autoclaves, fridges, etc., should be cleaned thoroughly with an appropriate disinfectant (e.g., bleach).
- Students should be discouraged from bringing sick animals into the lab. Animals that have died from unknown causes should not be permitted in the lab.
- Any animals kept in the lab should be maintained in a clean, healthy environment.
- No food should be stored or consumed in the lab or supply room.
- The use of formaldehyde should be avoided. Formaldehyde should not be kept in any school.
- Purchased specimens should be removed from preservative with gloves or tongs in a fume hood.
- When using specimens packaged in preservative, they should be rinsed thoroughly in running water and soaked in water overnight.
- As an alternative, it is recommended that vacuum packed specimens be used.
- Specimens should be discarded in biohazard bags immediately after dissection as there are some species of bacteria that can begin to grow even on specimens which have been in preservatives.
- Before taking students on field trips, teachers should become familiar with any dangerous plants or animals which may exist in the area (e.g., stinging nettles and poisonous plants).
- All discarded plant and animal remains should be placed in a garbage can that has been lined with a plastic garbage bag.
Specific Laboratory Operations
A number of specific laboratory operations deserve special attention when micro-organisms are involved.
Pipetting--the greatest hazards are
- production of aerosols
- accidental ingestion of fluid
- contamination of the mouthpiece
The last two hazards can be eliminated by the use of a pipetting bulb.
To prevent the first hazard (production of aerosols)
- never use a pipette to bubble air through a contaminated liquid
- never blow a liquid out of the pipette forcefully
- always discharge the pipette with the tip below the surface of the receiving liquid
Immediately after use, contaminated pipettes should be immersed in a germicidal solution, and then autoclaved.
Syringes--the greatest hazards are
- accidental inoculation
- aerosol production
Inoculating Loops
Use care, as the film held by a loop may break and cause atmospheric contamination. A hot loop may cause a liquid to spatter when it is inserted. Allow it to cool first. A contaminated loop may produce an aerosol by boiling and volatilization when it is placed into a flame for sterilization, even before all pathogenic organisms are killed. Whenever inoculating loops are used, any actions that might result in the generation of an aerosol -- jerky motions, shaking the loop, and agitating liquids -- must be avoided.
Teachers should dip inoculating loops into ethanol before flaming (prevents aerosol formation).
Caution: Care must be taken because of the flammability of ethanol.
Centrifuges
Centrifuges can be cleaned with ethanol to kill any bacteria present (use the fume hood).
Growing Bacterial Cultures
There is always the possibility of a few spores of pathogenic bacteria being introduced from the atmosphere. Be sure the culture medium is properly sterilized by autoclaving. After inoculating the medium with bacteria, be sure to wash hands and clean up any spills with a good disinfectant.
It is recommended that disposable petri dishes be used. When finished with the bacterial cultures, the dishes should be collected in a bio-hazard plastic bag and then autoclaved before disposal.
Use of Human Tissue and Fluid
A recent medical review about the potential risk of transmitting hepatitis or AIDS (acquired immune deficiency syndrome) through the extraction and analysis of samples of human fluid or tissue has led to the complete elimination in Manitoba schools of these experiments or demonstrations. Prepared slides for teaching purposes are available from supply houses.
Infectious Agents
Nearly all groups of micro-organisms have some effect on people. The various groups and some of the diseases for which each group is responsible are shown below.
| Micro-organism | Human Disease |
|---|---|
| bacteria | diphtheria tuberculosis rheumatic fever pneumonia |
| viruses | chicken pox measles mumps poliomyelitis |
| fungi | athlete's foot systemic mycosis |
| rickettsiae | typhus Q fever rocky mountain spotted fever |
| protozoa | schistosomiasis malaria giardiasis |
Each group is responsible for many more diseases than listed. All groups of micro-organisms contain some pathogenic members. Consequently, experiments which may involve micro-organisms either directly or indirectly must be strictly controlled.
Teaching About Biological Hazards
Teachers should discuss biological hazards as they appear in the context of laboratory activities.
Suggested Lesson Plan
Placement:
Science 7 Microbes and Ecosystems
Senior 1 Science Safety Orientation
Senior 2 Science Introduction to Biology
Senior 3 and 4 Biology Microbiology Unit
Possible student assignments include
- writing a report on specific micro-organisms detailing where they are found, the diseases they cause, and the cures, if any
- making posters about each specific group of micro-organisms
The term radiation can be and is applied to any physical property which "radiates" outward from a source. It is applied to many physical phenomena including the entire electromagnetic spectrum, high energy particulate emissions from radioactive sources, and even sound and ultrasound. Radiation may be transmitted, absorbed, or reflected by a particular medium.
It is generally classified into two distinct groups, Ionizing and Non-Ionizing. The distinction lies in whether or not a particular type of radiation has the ability to strip electrons from the atoms (to "ionize") in a medium in which the radiation is being absorbed. Because of the unique properties of these two classes of radiation, they are discussed separately.
Biological Effects
The process of ionization can break molecular bonds, thereby altering the chemical structure of the target material. If the affected molecule is part of a critical structure within a cell in the human body, the function of that cell may be altered. This may result in cell mutation, cell malfunction, or cell death. Such interactions occur constantly as a result of exposure to naturally occurring background levels of ionizing radiation (e.g., from cosmic rays) and chemical agents. The body has evolved repair mechanisms to correct this damage.
Such cellular alterations may ultimately result in carcinogenesis. No threshold level of radiation exposure exists above which carcinogenesis occurs. Rather, the risk of cancer later in life increases with increasing exposure. However, the exposure received from working with typical sources of ionizing radiation in the school environment is extremely small (much less than accumulated exposure from normal background). The associated risks are much much lower than the health risks of everyday activities, such as driving a car, swimming, or cycling.
At extreme ionizing radiation exposure levels, the resulting damage can exceed the body's natural repair capabilities. This can cause directly observable effects (e.g., skin burns, cataracts, or even death). However, this requires exceptionally high exposure levels which are simply unattainable from the types of ionizing radiation sources available in the school environment. Use of such sources is heavily regulated and they are only available in specialized applications (e.g., cancer treatment, nuclear power production, and industrial processing).
Sources and Types of Ionizing Radiation
The following are all common forms of ionizing radiation which may be encountered in the laboratory.
Emissions from radioactive
materials include
alpha particles
beta particles
gamma rays
Cathode Rays A cathode ray is a stream of electrons accelerated from a cathode or negatively charged electrode. If accelerated across sufficiently high voltages, the high speed stream of electrons is capable of ionization. Cathode rays are normally produced in a vacuum inside sealed glass tubes (called cathode ray tubes or CRTs).
In practice, their penetrating power is low and in most instances they are completely absorbed by the glass walls of the tube. However, at very high voltages and/or for very thin walled tubes, cathode ray leakage is possible. It is prudent practice to keep operating voltages on demonstration type tubes below 5 kV. Once cathode rays have been absorbed and given up their energy, they are simply ordinary electrons.
X rays X rays may be produced as secondary radiation from CRTs or other vacuum or discharge tubes operating at voltages above a few kV. X ray production occurs as a by-product when the accelerated electrons are absorbed. In general, X rays penetrate much more effectively than cathode rays; but in practice, their penetrating power is still sufficiently low that in most instances they are completely absorbed by the glass walls of the tube. However, as with cathode rays, at very high voltages and/or for very thin walled tubes, X-ray leakage is possible. When absorbed, the energy in an X ray is converted into other forms of energy (e.g., heat) and the X ray ceases to exist.
Radioactive Materials When dealing with ionizing radiation, it is important to remember that the terms radioactive and radiation are not interchangeable. The term radioactive specifically refers to any material which spontaneously undergoes a nuclear transition, with the concomitant emission of ionizing radiation. The radiation emitted may be in the form of a high energy particle (e.g., alpha or beta), a photon of electromagnetic energy (gamma rays), or both.
Alpha particles consist of two neutrons and two protons bound together. They are emitted at very high energies from the nuclei of some types of radioactive atoms. Because of their large size, they are easily absorbed by materials as thin as a sheet of ordinary paper. Once they have been absorbed and given up their energy, they are identical to an ordinary helium atom.
Beta particles are high speed electrons ejected from the nuclei of radioactive atoms. Physically they are comparable to cathode rays but they usually have much higher energies than the cathode rays produced in a typical CRT. Once they have been absorbed and have given up their energy, they are identical to an ordinary electron.
Gamma rays have physical properties which are identical to X rays. Gamma rays usually have much higher energies than any X rays produced by demonstration-type apparatus. As with X rays, when the absorbed energy in a gamma ray is converted into other forms of energy (e.g., heat), the photon ceases to exist.
A wide range of low activity radioactive sources are commercially available. Sealed sources usually consist of metal or plastic discs or rods containing radioactive material. Unsealed sources may be in the form of liquids or powders. Except for extremely low activity sources, an Atomic Energy Control Board (AECB) license is required before facilities can obtain radioactive sources.
Ionizing Radiation Protection Procedures
Protection of staff and students from exposure to radiation requires careful planning of experimental set ups and procedures and the maintenance of all radiation sources in good order. All potentially hazardous equipment and materials must be available for use only under the direct supervision of a teacher who is familiar with safe procedures. The onus is on the teacher to be aware of potential dangers and to convey this information to the students. The teacher must instruct students in proper operating and handling procedures and must insist that they be followed.
The two distinct types of ionizing radiation hazard are external exposure and personal contamination. Exposure refers to exposing the body to a radiation field. Ionizing radiation causes ionization within body tissue as the radiation emits energy. It is this transfer of energy via the process of ionization which results in tissue damage. Radiation exposure does not make you radioactive. Once the particle or photon has transferred its energy and been absorbed, it no longer presents a hazard. When you switch off an X-ray tube or CRT, electron acceleration and secondary X-ray production ceases immediately, there is no residual radiation, and no radioactive material is produced.
The principle methods of minimizing radiation exposure are time, distance, and shielding. Exposure is directly proportional to time: the longer the exposure the greater the potential damage and risk. Therefore, minimizing exposure time minimizes damage and risk. Exposure is inversely proportional to the square of the distance from the radiation source (i.e., inverse square law). This means that doubling the distance from the source reduces exposure to 1/4, tripling the distance reduces exposure to 1/9, and so on. Therefore, maximizing the distance from the source is an effective method of minimizing exposure. Finally, shielding simply means blocking the radiation with a suitable material. Alpha particles can be completely absorbed by very thin light materials, such as a sheet of paper. Beta particles and cathode rays are more penetrating, and may require a sheet of foil or a glass or plastic case for shielding. X rays and gamma rays are generally much more penetrating, and may require one mm to a few cm of lead for shielding.
Contamination refers to contaminating the body with radioactive material. When working with unsealed radioactive sources, it is important to make sure that the material is not spilled on the skin, ingested, or inhaled. Tissues contaminated with radioactive material are constantly being exposed to the radiation produced by that material. Once again, it is the ionization caused by this radiation which is the principle mechanism of tissue damage.
In addition to using the principles of time, distance, and shielding to minimize radiation exposure when working with unsealed radioactive sources, special precautions should be taken to minimize the potential for contamination. These precautions are similar to those for handling laboratory chemicals (i.e., wearing rubber gloves, lab coats, goggles and masks, using proper utensils to handle material, using established clean-up procedures, and eye and skin wash stations).
Finally, it is recommended that suitable radiation monitoring equipment (e.g., a pancake style Geiger-Muller detector) be available for use when working with any source of ionizing radiation. This equipment must be maintained in good working order. Training must be provided for persons using radiation monitoring equipment.
How to Cope with Spills of Radioactive Compounds
The immediate washing of contaminated areas with water and soap is the preferred method for removing loose contamination, subject to certain elementary precautions including
- using tepid water
- using soap that is not abrasive or highly alkaline
- washing and scrubbing with a soft brush to avoid abrading the skin
- washing the skin for a few minutes at a time, then drying and monitoring
- placing used towels and wiping cloths in a separate plastic bag for subsequent disposal
Washing could be repeated if necessary (as indicated by monitoring) providing there is no indication of the skin getting damaged. Attempts to remove contamination which resists mild procedures should only be made under medical supervision.
Caution: Use of organic solvents and/or acid or alkaline solutions must be avoided.
Storage of Radioactive Material
Storage of radioactive material should conform to
- restricting possession of radioactive materials to the minimum quantities required
- placing radioactive material in a suitably shielded container (e.g., a lead storage pot)
- storing it in a locked and properly marked cabinet or safe, with a copy of the current AECB radioisotope license
- locating the storage cabinet in an area not frequently used by people (e.g., a storeroom that is close to lab where material is used)
- ensuring that the storage location is known to the safety officer and school administration in case of a fire
- maintaining an inventory of radioactive material that is made available to the AECB upon request
Transport and Disposal of Radioactive Material
Transport or shipping of any radioactive material outside of the laboratory for any reason is subject to the AECB's Transport Packaging of Radioactive Materials Regulations and to federal and provincial transport of dangerous goods regulations.
Radioactive material must be returned to the supplier for disposal or to the Waste Management Operations at Chalk River Laboratories, Atomic Energy of Canada Limited, Chalk River ON, K0J 1J0 (prior arrangements must be made. Telephone: 613-584-3311, ext. 3650, fax 613-584-1438). Any other waste disposal method requires specific approval by the Atomic Energy Control Board.
Accidents and Unusual Operating Conditions
Procedures include
- alerting the teacher immediately if the equipment does not appear to be operating correctly, if an unexpected radiation exposure is suspected, or if a radioactive spill occurs
- turning off electrical equipment before leaving the work area if the experiment cannot be completed as planned for any reason
- ensuring radioactive sources are returned to proper storage (never leave sources unattended)
- using radiation monitoring equipment to verify that radioactive sources have been properly returned to storage and that there is no residual contamination in the work area following use of radioactive sources
Biological Effects of Non-ionizing Radiation
Human tissue interacts with this type of radiation in fundamentally different ways than it does with ionizing radiation. As its name implies, non-ionizing radiation does not ionize atoms or molecules, but can increase their kinetic energy, or "vibrate" them (i.e., transferring the radiation energy to tissues through heat production). Heat production is the main effect of exposure to infra-red, microwave, and radio frequency radiation.
At sufficiently high radiation intensities, normal physiological processes can be disrupted and, accordingly, limits on the strength of the electric and magnetic fields, or the "power density" in some cases, are specified for human exposure in publications such as Health Canada's Safety Code 6 (Limits of Exposure to Radio Frequency Fields at Frequencies from 10 kHz - 300 GHz). It is not generally necessary to measure actual field strengths in the school laboratory for comparison with the specified limits when safe laboratory practices are followed (e.g., using low intensity radiation sources and minimizing exposure), .
The tissue-penetrating ability of non-ionizing radiation is related to its wavelength. Short wavelength ultraviolet rays are absorbed by the skin and the cornea and conjunctiva of the eye, causing a burn-like reaction when the radiation intensity or combination of intensity and exposure time is sufficiently high. Sunburn and the painful "welder's flash" burn of the eye are familiar effects of ultraviolet radiation exposure. In contrast to this acute type of radiation-induced injury, prolonged or chronic exposure to ultraviolet radiation may result in more serious effects such as premature skin aging or skin cancer.
Sources and Types of Non-ionizing Radiation
Types that may be found in school laboratories include:
Visible light (including spectroscopic sources such as mercury, hydrogen, iodine, and sodium vapour discharge tubes)
Ultraviolet Lamps and Electric Arcs Ultraviolet lamps, such as those used to detect the presence of certain compounds by their fluorescence, must be used in such a way that the source can never be viewed directly. Electric arcs produce very high intensities of ultraviolet radiation and must never be used as an open source. If an arc is used to provide intense visible light, it must be enclosed except for an exit pupil where a filter can be used to absorb ultraviolet light from the desired visible light beam.
Lasers The visible beam of light from a laser is focussed by the lens of the eye and can cause severe retinal damage with very brief exposure when the laser is of sufficient power. For this reason, the Canadian Radiation Emitting Devices Regulation specifies that demonstration lasers for educational institutions be limited to 1 milliwatt beam power and be within the wavelength range from 400 to 780 nanometres (visible).
For lasers meeting these criteria, the normal blink response time (0.25 seconds) of the eye is sufficient to prevent retinal damage. In addition, lasers must be used under the close direction of a teacher, usually in a well-lit room so that the pupils of the eye are small. Lasers should be positioned in such a way that the beam cannot enter a person's eye, either directly or by specular (mirror-like) reflection. It should also be noted that the direct or reflected viewing of any intense visible light source -- such as electric arcs, burning magnesium ribbon, the Sun, and collimated or focussed beams from ordinary tungsten lights -- can cause retinal damage.
Microwave Generators The microwave radiation generators used in school laboratories for demonstration purposes produce low intensity microwave radiation. Exposure to microwave radiation may produce biological effects (such as tissue heating). Care should be taken to minimize the exposure of students and staff through measures such as preventing access to the beam by shielding its path and restricting admittance to the area through which the beam passes.
New microwave ovens sold in Canada must not leak radiation above levels specified in the Canadian Radiation Emitting Devices Regulations. Ovens used in cafeterias, and home economics and science laboratories may present a hazard from microwave radiation leakage if the door or door seals have been damaged through use (e.g., closing the door accidentally on ovenware items prevents the original tight door seal). If damage to an oven has occurred or is suspected, leakage radiation levels should be measured.
Infra-red and Radio Frequency Infra-red and radio frequency radiation sources used in schools are usually of low intensity and used only occasionally. If these practices continue, infra-red and radio frequency radiation do not appear to present significant hazards. Any change in these practices should be accompanied by appropriate precautions to reduce the exposure of students and the teacher to the radiation.
Non-ionizing Radiation Protection Procedures
Protection of staff and students from exposure to non-ionizing radiation requires careful planning of experimental set-ups and procedures and the maintenance of all radiation sources in good order. All potentially hazardous equipment and materials must be available for use only under the direct supervision of a teacher who is familiar with safe procedures. The onus is on the teacher to be aware of potential dangers and to convey this information to the students. The teacher must instruct students in proper operating and handling procedures and must insist that they be followed.
The basic objective of radiation protection is to minimize the radiation exposure of persons who are required to handle radiation sources. Measures that can be used with non-ionizing radiation include
- ensuring that students follow procedures exactly as specified by the teacher
- never looking directly into a laser beam, ultraviolet radiation source, or bright light
- keeping the time for potential exposure at a minimum
- staying as far from the source as possible, because radiation intensities generally decrease with distance from the source (laser beam intensities do not change significantly over distances comparable to the dimensions of school laboratories; the same may be true for radiation from focussed microwave and radio frequency antennas)
- knowing what kind of shielding is effective in absorbing the type of radiation encountered (ensure that a sufficient thickness of shielding material is available and be sure to use it)
- knowing what type of personal protective equipment is suitable for the radiation you encounter (be sure that protective UV goggles are specifically designed for that application; if hands are exposed to UV radiation, while you are setting up or conducting an experiment, wear appropriate protective gloves)
Accidents and Unusual Operating Conditions
Procedures include
- alerting the teacher immediately if the equipment does not appear to be operating correctly or if an unexpected radiation exposure is suspected
- turning off electrical equipment before leaving the work area if the experiment cannot be completed as planned for any reason
- storing or consuming food and beverages, chewing gum, and smoking in an area where toxic materials are used food, beverages, and cigarettes can readily absorb toxic vapours or become contaminated with unseen toxic dust. Poisons may be transferred from hands to food and cigarettes.
