Electrical safety

This talk is about electricity on this job: the building we are opening up, the tools we plug in, and any overhead line or buried cable we could reach. HSE's page on electrical systems in buildings says electricity can kill, and that unlike most other hazards you cannot see it, feel it, hear it or smell it, so there is no warning. The law says you must take precautions against death or injury from electricity during construction work. Refurbishment is the greatest risk, and it has to be planned, managed and monitored. Specialist electrical work is only for people who are trained and competent, following strict procedures. The equipment has to be safe and maintained.

HSE says about three workers are electrocuted each year during refurbishment on commercial and domestic buildings. Further deaths happen in incidents with overhead power lines and underground cables. I am using that figure as HSE states it. I have not updated it. Incidents inside buildings involve electricians and other trades. They happen when equipment was assumed to be dead but was live, or was known to be live and the precautions were not enough. Plumbers and joiners are named, not only electricians. Electricians are not immune either. HSE says a number of the electrocutions involve qualified electricians.

The people planning a refurbishment have to understand the electrical system and talk to the occupier, so the work does not compromise the system or the people. If the work, including labouring, joinery or plumbing, is liable to disturb or damage the existing system, the relevant parts should be isolated. Electrical contractors should not work live if it can be avoided, and they should not make a system live before the work is finished and everything is installed correctly. Safe isolation procedures must be followed at all times. A chat photo of a consumer unit is not isolation. If we do not know whether it is dead, we treat it as live and we stop until someone competent has isolated it and proved it.

Tools are the everyday risk. HSE says tools, plugs and cables designed for DIY and domestic use are not suitable for site conditions. Use cordless tools, or tools on a 110 volt centre-tapped-to-earth supply, so the maximum voltage to earth does not exceed 55 volts. Inspect power tools regularly and take them out of service if they are damaged. A qualified electrician services them. No makeshift repairs. Where 230 volt mains equipment is used, the risk is high if a tool, a lead or the equipment is damaged or faulty. HSE's checks for 230 volt equipment are a visual check for damage every shift, a visual inspection every week, and a combined inspection and test before first use on a site and then every month. Records of those checks should be kept. An RCD detects some faults, not all of them, and switches the supply off quickly. It has to be properly installed and enclosed, checked daily, treated with care, kept free of moisture and dirt, and protected against vibration and mechanical damage. An RCD is not a reason to leave a damaged lead in use.

Lighting on a temporary system needs the same care. Protect cabling and bulbs. A broken bulb can leave a live filament. Check bulbs so the site stays both electrically safe and well lit. The fire talk covers lamps as an ignition source. This talk covers the shock.

Overhead lines are a separate hazard, and ladders, scaffold tubes, tippers, lorry-mounted cranes and MEWPs are on HSE's list of what reaches them. Accidental contact kills people and causes serious injuries. So does a flashover, when a person or an object gets too close without touching the line. Going close can be enough. Voltages lower than 230 volts can kill. Do not mistake a line on a wooden pole for a telephone wire. Electricity can bypass wood, plastic or rubber if it is damp or dirty. Do not rely on gloves or rubber boots. Assume a line is live unless the owner has proved otherwise. Find out whether a line crosses the work or the access before you arrive with a high vehicle. The information comes from the distribution network operator. If a line is there, talk to the owner in time for it to be diverted or made dead, or for other precautions.

HSE's order is to eliminate the danger where you can: do the work somewhere else, have the line diverted, or have it made dead. If you cannot, control the access and the work. Barriers go at the clearance distance the distribution network operator gives you. Passageways under a line should be as narrow as the plant needs and should cross at right angles where possible. If work under a live line cannot be avoided, use barriers, goal posts and warning notices, keep anything that could reach past the safe clearance out of the area, and put physical restraints on cranes, excavators and telehandlers so they cannot be altered on the day. Someone suitable supervises the plant. The ladder talk includes HSE's rule: do not work within 6 metres horizontally of an overhead line unless it has been made dead or protected with insulation.

If a vehicle or a load touches a line, HSE says stay in the cab and tell the distribution network operator immediately. Warn everyone else to stay clear. Try to drive clear. If you have to get out because of fire, jump clear. Do not climb down the steps. Never try to untangle the equipment until the owner of the line has confirmed it is dead and safe. A line can trip out and then re-energise on its own, without warning. Keep the operator's number in the cab and on the phone before you need it.

Buried cables are on the same HSE page as a cause of further deaths. This talk does not invent a scanning method. If we do not know where the services are, from the occupier, the drawings, or the operator, we do not dig, drill or drive a pin through them. We stop and find out. Today: what is live, what has been isolated and proved, what voltage the tools are on, and where any line crosses the access. If the answer is that we are not sure, we do not start.