Safety is no Accident

This page was specifically written for those who build Tesla coils and other high voltage devices, much however also applies to other areas of thise site, I will leave it up to you to consider which parts apply to you. Let's start off by getting a few points clear before we look at specifics:

• Accidents don't just happen, they have causes.
• Accidents are caused by people, especially those who are ignorant or careless.
• The chances of an accident increase with tiredness, the consumption of alcohol, or the use of certain drugs.
• A hazard is a physical entity, which in certain circumstances may result in death, injury or damage.
• A risk is the chance of death, injury or damage resulting from exposure to a hazard.
• It is our responsibility to either remove a hazard, or failing that to reduce the risk to as small a level as possible.
• We have a responsibility for the safety of others who may be affected by our activities.
• Those of us who take part in more extreme activities are exposed to correspondingly greater risks and hazards.
• Before we operate our high voltage devices, or indulge in other hazardous activities, it is sensible to conduct a risk assessment. In fact in the UK, and I guess elsewhere, there is a statutory obligation to perform a risk assessment if we were to use any hazardous material or apparatus or procedure in a place of work (Health and Safety at Work Act, & the Electricity at Work Regulations etc.)

The hazards involved in high voltage experimentation are more complex than is probably immediately apparent. Although some hazards will be common to all of us who generate and use high voltages, if we make our own apparatus then we will be subject to additional ones. The hazards may be divided into a number of specific areas:

• Electrical
• Mechanical
• Chemical
• Electromagnetic radiation

Electrical Hazards

Considering the obvious hazards involved with electricity, it seems strange how many risks people take. For a variety of reasons to be covered shortly, the highest risk of death or injury from electrical causes is probably the ordinary household supply, be it 117V 60Hz or 230V 50Hz, it doesn't actually matter much. A survey of households in the UK, a few years ago, revealed that 75% of mains plugs were incorrectly wired. For example wires were transposed, cable clamps not fitted, and long lengths of conductor were exposed.

In a previous job, I examined thousands of items of professional electrical equipment in laboratories. In every laboratory there were pieces of equipment that were badly wired or maintained.

It has been said that it is volts that jolts, and its mils that kills. In reality it takes only a few dozen volts to kill somebody, provided that sufficient current flows, and that it flows through critical organs. The truth is that it is the amount of power that is disipated that matters. Remember it takes voltage to drive current through the body, and that for a given voltage the lower the resistance of the circuit the more current flows. We have, therefore, a number of variables.

The path that a current takes through a body also matters. Many of us will have taken a shock across our fingers without harm except perhaps for a minor burn. If that current had been across the head, or even hand to hand, the story might have been different.

As well as the route a current takes, the electrical resistance of the skin and the skin contact area are also significant. An older person's skin is naturally drier than a child's, and therefore a child is more at risk from electric shock than an adult. Wet skin and large contact areas will of course increase current flow.

Another significant matter is that of frequency. Much of what has been said and written is still open to discussion. Nerves are unable to respond to frequencies much above 700Hz, but this does not mean that they are not going to be damaged. In fact damage is probably more likely. At higher frequencies there is a tendency for currents to flow near the surface of conductors, the so-called skin effect. The higher the frequency the greater the skin effect.

Despite what is often suggested skin effect has but little effect at the frequencies used in Tesla coils. Moreover skin effect does not reduce the risk of damage to the human body, as the body is a complex conductor, and the inner organs are better conductors than the surface tissues.

Chemical Hazards

The existence of chemical hazards seems, at first glance, less of a problem than others. The reality is rather different. To start with some of the materials we use in the building of high voltage apparatus are hazardous, for example various solvents. Solvents generally are flammable, but more significantly in many ways, most of them are toxic to some degree or other. Even ethanol causes liver and kidney damage, higher alcohols are even more toxic. Halogenated organic compounds are also toxic in most cases, and the breakdown products produced when many of them are subjected to heat are extremely toxic.

Other substances, which under normal circumstances are harmless, can cause a hazard. As an example glass is regarded as fairly inert, but ground up into dust or in the form of fine fibres and inhaled it causes silicosis.

Another area of concern is ozone. Ozone is oxygen with a triatomic molecule (O₃ ) rather than diatomic (O2). It is far more reactive, and is actually toxic to all life forms on earth. At one time it was thought to have life-enhancing properties. Today we know better, and commercial devices that produce ozone have to have either filters or exhaust devices fitted. High voltage discharges produce ozone in appreciable quantities, whether the discharges be in the form of arcs or corona.

Electromagnetic Radiation

Electromagnetic radiation (EMR) is a subject that has caused much debate in the last few years. To my mind it seems probable that there is no level of electromagnetic radiation that is without some effect upon the body., However it is generally agreed that the higher the frequency of radiation, the greater the risk. The problem for humans is that with the exception of that very narrow part of the electromagnetic spectrum we call visible light, we are unable to detect it without special instruments.

In addition to the frequency we have to take note of the field strength of the radiation.

The most significant forms of electromagnetic radiation as far as health is concerned are what are known as the ionising radiations, that extend from the ultra-violet and upwards in frequency, including X-rays & gamma-rays. UV light is produced in electrical arcs and by electrical discharge through many gases, including air and mercury vapour. Eye damage is easily caused by looking at electrical arcs, don't do it, you won't see anything anyway.

For the high voltage experimenter the other form of EMR that we have to be particularly aware of is X-rays. X-rays are produced when electrons with sufficient energy collide with atoms. Accelerate electrons through a vacuum at 10kV (producing electrons of 10keV energy) and the chances are that you are producing X-rays. In the earliest X-ray tubes thre electrons only had to strike the glass wall of the tube in order to produce significant radiation. If you have vacuum devices and connect high voltages to them and you observe a greenish glow then you have got sufficient X-radiation to damage your health.