Electricity kills! Every year many people at work, including electrical contractors and installers, suffer electric shocks and burns. Other injuries, such as falls, are caused as a result of a shock. Voltimum UK Managing Editor James Hunt looks at the issues, especially with regard to power tools:
Power tools are potentially dangerous devices. Looking at the DIY sector, which is where a large number of power tools are sold, every year there are around 70 deaths and 250,000 injuries. Of these, around 100,000 are injuries seriously enough to require a visit to casualty. The majority of such accidents occur because of carelessness or a fundamental lack of knowledge. Where professionals are concerned, such as electrical contractors and installers, the accident rate, as would be expected, is far lower; even so, many bad accidents do occur, and for broadly similar reasons.
What voltage to use?
As a general rule the lower the voltage used, the lower the risk of a serious electric shock so, wherever possible, portable electrical tools should be battery operated, otherwise they should (ideally) be supplied through a double wound 110V centre-tapped transformer. Note that portable electrical appliances, such as power tools, of 240V or above should not be used outside a building, and for obvious reasons, (electric motors can spark) never use power tools, including cordless ones, anywhere near flammable liquids or in gaseous or explosive atmospheres. Another option is to use tools supplied from a SELV system with a maximum operating voltage of 50V AC. However, such tools are not readily available and other options will usually be adopted.
Before using any mains-powered power tool, find out who is responsible for health and safety in the workplace (in reality, this is everybody), even though some people may have specific responsibilities. Also check that the voltage and frequency are compatible with the supply - this is especially important on building sites, and especially in quarries (where cable may be run under water), as there is the 110V requirement. Note that protective multiple earth (PME) supplies are not suitable for quarries because it is not possible to ensure that the electrical bonding of all metalwork, as required by the Electricity Safety, Quality and Continuity Regulations 2002, is always in place. Note also that there is no legal requirement to use 110V onsite; many would argue that 230V tools used in conjunction with an RCD is just as safe. Even so, 110V centre-tapped to earth (CTE), which limits shock voltage to earth to 55V, is generally enforced on UK sites, and in 50 years, there has apparently been not a single fatal accident! The HSE is not keen on higher voltage powered tools being used, but cannot dictate mandatory use of 110V because of EU Directives.
In dry conditions, the safety of a CTE system can be improved still further by using Class II (all insulated or double insulated) hand tools. These should comply with BS EN 60745 (or BS EN 50144 for older equipment). The transformer/genset supplying the 110V should be outside the location concerned. Transformers should be of the double-wound isolating type to BS 3535 (see also BS EN 60742 and BS EN 61558). If a generator supplies the power, its windings should provide electrical isolation equivalent to that of an isolating transformer.
Cordless or mains powered tools?
For ultimate power, mains powered tools should be used, but modern batter-powered cordless tools have plenty of power and torque, are more portable, and are definitely much safer electrically.
Portable power drills (often cordless today) are by far the most widely used power tools, and they often receive very heavy usage - so need careful checking of their capacity limitations (see owners' manual) for safety. Note that cordless power tools are subject to health and safety regulations, just as mains-powered machines are.
In general, when using mains-powered tools, always check that there is no damage to the power cord. In this respect, cordless tools are safer as there is no power cord, and also there is much less risk of electrical shock as operating voltages are significantly lower (usually to 24V maximum).
Some basic power tool safety rules:
Firstly, when buying a power tool, ensure that it has been approved by an approved body, such as TUV, and always read the user manual carefully. The following are some basic additional (and fairly obvious) safety rules:
- Only use a power tool for its original purpose.
- Keep power tools away from water.
- Do not use power tools if damaged.
- ALWAYS unplug power tools after use.
- NEVER mess around with power tools.
- Don't put a power tool down until it has completely stopped.
When deciding on the safety of power tools, the following other factors should be taken into account:
- What type of power tool is it?
- Is it hand-held or not?
- Are there manufacturer's recommendations?
- What is the power tool's integrity?
- How old is it and what has its duty cycle(s) been?
- What is the power tool's working environment - is it damp or dusty, etc?
- Is there likelihood of mechanical damage?
- Have any repairs been carried out to the power tool?
Power tools that pose particular dangers are circular saws and grinders - the former for obvious reasons; the latter because they can break up and burst - the high speeds involved ensuring that a spray of heavy, sharp pieces fly unpredictably in all directions with considerable force. Incorrect use of circular saws all too often cause fingers (or worse) to be lost, and severe facial injuries and blindness can the result of a grinding disc (abrasive wheel) break-up. Even electric drills can be highly dangerous - though generally far less often than circular saws and grinders. In one case, a person using a power drill managed to get the power cord stuck in the chuck, which wrapped around the neck and strangled her to death.
Power tools include the following general types: powered abrasive wheel tools; portable circular saws; portable drills, including hammer drills (mains and cordless); mitre box saws and chop saws; and pneumatic tools (the latter rarely used by electrical contractors and installers).
Ensure that the trigger switch works correctly, and that the lock-on releases freely.
If there is any damage to the power tool (other than superficial scratches etc), replace it. With mains-powered tools, if there is any lead damage, replace it immediately.
A loose chuck can cause injury; ensure that it is tight on the spindle, especially with reversible drills, and ensure that the chuck key is removed from the chuck before starting the drill - a flying key can be dangerous. Also remember that, in the context of any revolving machinery, don't wear loose clothing and jewellery, and keep long hair out of the way.
Always wear safety goggles or safety glasses with side shields that comply with current standards - this is especially important where rotary hammer and hammer drills are concerned; even more with grinders (abrasive wheels). Training courses should be attended for operators of abrasive wheels, and the relevant Regulations are required by the Provision of Use of Work Equipment Regulations 1998. A full face shield should be used with certain work - such as with abrasive wheels - though it is clear that many users don't actually do this.
It is essential to hold power tools securely, by bracing against suitable stationary objects where they are available. This is safer, and is also likely to result in a better job. If a drill binds in the workpiece, release the trigger immediately. Cut off the power supply before removing the drill bit etc. Though this might be a pain, always unplug a mains powered drill before changing drill bits. Unplug drills immediately after use and when changing accessories.
Percussion tools and similar with rotating parts need similar considerations, but there may be greater risk of long-term accumulated injury through vibration. Take the necessary precautions, having consulted the operating manual.
Only use accessories designed for the tool otherwise injury could result. Blades are designed for specific cuts and materials, and incorrect selection can increase the likelihood of breaking teeth, kickback or blade fracture. Take care with blade selection, and ask the power tool manufacturer (or your electrical wholesaler) about variables such as tooth rake and material, number of teeth, and also pitch. This will help maximise safety. Never remove guards.
Special software is now available for those responsible for carrying out power tool risk assessments to protect users. Available today are packages that calculate Exposure Action Value (EAV), Exposure Limit Value (ELV) and HSE points, record productivity data (e.g. the number of holes drilled) and provide comprehensive data recording. Such software can integrate with a small item of equipment that can be attached to the power tool to record the user’s vibration exposure and usage time. The data is imported into the software to build a personal vibration exposure record.
Difficult working environments:
Humid or dusty environments may impair the degree of protection offered by a Class II portable tool, so Class I tools may be more suitable, but - even so - protection against electric shock in such environments always depends on earth path integrity and the suitability of the fault protection. Power tools have certain IP ratings (ingress protection) - this should be chosen according to the environment worked in.
Many power tools create fine dust particles themselves. These tools include saws, routers, spindle moulders, sanders, planers and grinders. Always wear a mask, if this is so, even though modern power tools have dust reducing designs and dust reservoirs (which must be carefully emptied from time to time.
Restrictive conductive locations:
Where a person using portable electrical equipment (such as a power tool) is in close proximity to, or in contact with, earthed metalwork, the consequences of an electric shock resulting from certain types of electrical equipment failure are likely to be serious or fatal. Such places are known as restrictive conductive locations and are defined in BS 7671. Any heat and humidity will make the problem worse through perspiration. Also, the power tool user may be tempted to remove clothing, which reduces insulation. The use of mains-powered power tools (and other electrical equipment) in such locations should be discouraged - battery-powered or pneumatic tools should be used instead.
Battery charging:
For cordless power tools, battery charging should, ideally, be carried out in a dry placed, away from all combustible materials, and preferably using the charger intended for it. Remember that battery shorts can cause fire or explosion, and that, unless the battery is removed, cordless tools can always be in a (potentially dangerous) operating condition. Dispose of old batteries properly.
Buried cables:
This is very important - always check whether live electric cables are located at or near where you are drilling. This author has direct experience of drilling through a live 220V cable in a wall with a drill - the result was truly spectacular and could well have been lethal. Hold the tool only by the insulated gripping surfaces to prevent electric shock if you contact a live cable. If cables are present, they must be disconnected, possibly by a suitably qualified person - in many cases, you, the installer. If a tool operator/electrical contractor gets an electric shock, identify the danger and DO NOT touch the victim - isolate the power supply, check breathing, check pulse and get help very quickly.
Breaking into a concealed water pipe is less dangerous (though quite exciting) but can be even more time consuming to fix. Check for these too.
Hand tools for electricians:
Non-powered hand tools for electricians are mainly screwdrivers, pliers, wire strippers and cutters, plus spanners etc. The general safety rules apply as for powered tools, although, of course, the dangers of electric shock or trauma injury are not the same as for power tools. However, users can still receive and electric shock through them under certain circumstances, and also be injured by using them incorrectly. The following, therefore, are safety tips for using screwdrivers:
- Choose contoured handles - there should be a flange to stop hand slippage.
- For slot screwdrivers, the blade tip width should match that of the screw head.
- Don't mix the Phillips type with the Pozidriv type.
- Use a vice to hold small workpieces (if possible).
- Wear safety glasses.
- A greasy handle can cause an injury through unexpected slippage - clean it.
- De-energise circuitry before beginning work on electrical equipment.
- If work must be carried out on 'live' equipment, the correct screwdrivers with insulated and non-conducting shaft MUST be used.
- Use a screw-holding screwdriver to get screws started in hard-to-reach areas.
The general rules are similar for other hand tools, though all have their own special characteristics, but remember not to cut or strip wires/cables unless you are completely sure that the circuit(s) concerned are de-energised and locked out securely.
Newey & Eyre has been warning contractors of the dangers of skimping on tool costs, pointing out that an insulated tool does not necessarily offer the same protection levels as VDE-rated tools – potentially the difference between life and death! Such testing can apply to both hand and power tools. All of the tools within Newey & Eyre’s Defiance VDE range are VDE tested.
Reputable hand and power tool manufacturers usually hold training courses on the effective and safe use of power tools. Take part!
