Section 7: Safety in control technology
7.1 Information for all teachers, including safety in non-specialist rooms
Teachers planning for safety in control technology should have thorough knowledge in this area. If this is not the case, teachers should seek advice from a specialist. Each school is required to develop, implement, and manage health and safety policies and procedures that are approved by the Board of Trustees. These policies and procedures are expected to be adhered to in addition to implementing the recommendations in this manual.
Before commencing work with students, teachers need to undertake an initial risk analysis of the production process to identify hazards in relation to:
- the people involved, such as students, resource personnel, and the intended end users of the outcome produced (including cultural and ethical considerations)
- the materials and equipment used, including energy sources and wastes
- the environment, for both the production process and location where the final outcome will be placed.
In good technological practice, students should also be made aware of the importance of risk analysis. This process should become an integral part of their classroom practice.
When hazards are identified, risks can often be minimised by incorporating procedures into the process.
In general classrooms, activities relating to control technology do not need to include soldering or the use of specialist chemicals. The types of activities undertaken depend more on teacher confidence and experience. But if programmes include activities such as soldering and printed circuit board (PCB) manufacture, then full safety procedures as outlined later in this section must be followed.
Generally, electronics and control activities involve simple circuit connections using separate components and basic connecting techniques, such as crocodile clip leads, screw posts, and banana plugs. A number of commercially available electronic and control technology kits have components that are simple to join and are easily disassembled. Because most electronic components are small, these should be mounted on a larger insulator base made of wood or plastic. This can help to prevent injuries. It can also make components easier to handle and easier to keep track of.
Dry-cell batteries can power most electrical circuits. Alkaline AA size or larger batteries are easy to handle and are long lasting. They should be of a non-toxic composition and should never be cut or penetrated. When batteries are not in use, remove them from the circuit or device to prevent short circuiting, overheating, and the battery casing from breaking down and leaking corrosive chemicals. This is especially important when equipment is stored for long periods of time. Be careful not to short out batteries as this can cause wires to overheat and catch fire.
It is recommended that students should not use any power supply over 30 V (volts) and have a circuit breaker (fuse) of no more than 10 A (amperes).
Teachers, and senior students under supervision, may use a low-voltage supply with an output current limited to 5 mA (milliamperes). If using a power supply connected to the mains, this must be SELV protected; that is, it contains an isolating transformer so that an earth fault in the circuit cannot put the user at risk of shock.
Examples of hazards in electronics technology are:
- burns from soldering
- fumes from soldering
- chemical stains and burns from PCB etching
- electric shock (where mains equipment is used)
- cuts from broken equipment, such as light bulbs
- injury from high-pressure air, for example, from pneumatics
- injury from high-pressure oil or water, for example, from hydraulics.
If students are involved in developing products for animal consumption, such as a controlled pet food dispenser, and wish to trial its suitability with animals, schools should have an animal ethics policy that meets the requirements of the Animal Welfare Act 1999 or any other legislation.
7.2 Additional safety in specialist areas
Control programmes in the specialist classroom may include various circuit-building technologies, such as soldering and PCB manufacture. Techniques such as these introduce hazards that must be controlled.
Small but painful burns can occur from contact with a hot soldering iron or, more rarely, from contact with a hot wire, such as during a short circuit. First-aid facilities must be available, including access to cold running water.
Compressed air and hydraulic fluids
Air and hydraulic fluids can be hazardous when under pressure. Air-pressure systems should be regulated and have a working pressure of not more than 320 kPa (kilopascals) = 46.4 psi. Never aim high-pressure air at any part of the body. Compressed hydraulic fluids, such as oil and water, can cause harm if they escape under pressure.
Cuts and lacerations
Light bulbs produce sharp glass slivers when they are broken. Keep a soft brush and pan to clean up breakages, then completely remove all fragments with a vacuum cleaner. The teacher should personally screw light bulbs into their sockets rather than leave this to younger students, who may overtighten them and break the glass.
Allowing students to use sharp blades for cutting materials such as thick cardboard or Veroboard is not recommended unless they have been adequately trained. If the teacher has any doubt about students’ abilities to carry out these tasks, alternative methods should be used.
For electronic circuits, 15 V of direct current (DC) is generally an appropriate maximum voltage. Commercial appliances, such as soldering irons and oscilloscopes, can be operated from the mains with safeguards. Staff and students should know where the safety cut-out switch is and how to operate it so that all electrical power can be quickly turned off in an accident.
Teachers should ensure electrical equipment has an electrical certification. A carbon dioxide or dry powder fire extinguisher should be kept on hand for electrical fires.
Printed circuit board (PCB) manufacture
Handling all chemicals for practical work in electronics should conform to Section 4 of Safety and Science: A Guidance Manual for New Zealand Schools. In particular, using strong ferric chloride or ammonium persulfate solutions in the manufacture of PCBs should be done only in a force-ventilated space, such as a fume cupboard. Students should wear safety glasses and protective clothing. Water should be available to dilute spillages, and waste solutions should be disposed of according to accepted environmental procedures.
When using Computer Numerical Control (CNC) routers and laser cutters in the production of PCBs, teachers and students must comply with the manufacturer’s recommendations and school health and safety policies. Some overall safety approaches are as follows:
- Always keep the area around CNC machines clear of obstacles.
- Always stack material where you can reach it but keep it clear from the machine’s moving parts.
- Always check that tools are sharp and set correctly.
- Always check that the correct tool data is entered into the CNC program.
- Always make sure that guards are in position while the machine is operating.
- Always make sure that all work and fixtures are clamped securely before starting the machine.
- Always make sure the spindle direction is correct for right-hand or left-hand operation.
- Always conduct a dry run to ensure the program is correct.
- Always check that limit switches (micro) are working correctly.
If soldering is to be a common feature of the programme, the classroom should have a suitable soldering facility positioned away from taps, basins, gas outlets, and flammable materials such as curtains. The bench material should be heat and chemical resistant, with a place to store the hot iron. The hot iron needs to be rested in a soldering station isolated from anything that’s flammable or that might be damaged by heat – and where students will not touch it accidentally.
Students should be taught to ensure the supply flexes of soldering irons are sound before switching them on and to report to the teacher any damage that occurs during use. The risks will be minimised if the non-burn variety of soldering iron flexes are fitted.
For most student work, soldering irons of less than 25 W should be used. Temperature-controlled units are more versatile.
After use, soldering irons should be unplugged and allowed to cool before being stored. The cooling process may require removing the irons to a safe area so that students do not touch them accidentally.
All students should be taught how to use a soldering iron safely, including the correct way to plug and unplug them without putting stress on the leads. Students should be made aware that the metal barrel of the iron is as hot as the tip. Most burns are caused by contact with the barrel. Another danger is flicking the iron to remove excess solder.
This may cause burns to the clothing, the skin or, more seriously, the eye. All students using soldering irons should be taught how to remove excess solder without flicking or shaking the iron. Also, when using a soldering iron or when near another person using one, students should wear suitable safety glasses, preferably of the ventilated type with side protection.
Solder contains a mixture of metals, including lead, which is a cumulative poison. It is not absorbed easily through the skin, and it is not vaporised much when solder is melted. Lead can, however, be transferred to the fingers. From there, it may be transferred to food and swallowed, so facilities must be available for students to wash their hands after soldering.
The heated flux produces fumes, so there should be enough ventilation in the room to prevent fumes from building up. Fumes can cause allergic and asthmatic reactions in some students, and teachers should be aware of students who are at risk. Where natural ventilation is not sufficient, suitable extraction equipment should be used. This could include an extractor fan rated for the volume of the room, vacuum extractor equipment to draw fumes directly from the soldering iron, or portable extractor fans with active filters attached.