One of the most common sayings among those who work with electricity is that voltage is what is felt, while it is current that actually does harm. There is, in fact, truth to this advice, as even relatively low voltages can produce currents strong enough to stop the heart or otherwise endanger workers.
As anyone who has studied the subject knows, the current passing through a circuit is proportional to the voltage potential in it, but inversely proportional to its resistance. Although it is less often focused on by those outside of the industry, then, resistance is a critical piece of the puzzle.
In virtually every case, for example, electrical safety measures insist on ensuring, among other things, that appropriate circuit resistance is maintained at all times. An unanticipated drop in resistance can result in skyrocketing currents, a problem that can snowball into a whole host of other dangerous issues. When currents rise beyond expected bounds, for example, wire insulation and electrical components can melt, leading to even bigger problems.
Nowhere is this phenomenon more obvious than with the class of electrical events known as "arcing." An electrical arc occurs when a current passes through the air between two parts of a circuit, instead of remaining confined to wires, as it was meant to be.
In addition to directly exposing workers to naked, unharnessed electricity, an arc can lead to even worse problems. If the strength of the current is high enough, the corresponding increase in the temperature of the air it passes through will further lower the resistance of the circuit that is created.
As has been seen, that will result in the flow of even stronger currents. As at least one arc flash training video points out, this sets up a self-reinforcing cycle whereby increased currents contribute to even more heating of the air, resulting in still lower circuit resistance.
The government's mandated osha arc flash training singles this out as one of the most pointed dangers facing those who regularly work with electricity. A widely distributed arc flash training powerpoint, for example, notes that the resulting explosion can be deadly to people dozens of feet away, whether directly or through the destruction of facilities and equipment it causes.
Given the dangers involved, then, it is easy to see the value in good, well-grounded arc flash consultants. Controlling the resistance of circuits and ensuring that electricity is never given the opportunity to form an arc are the cornerstones of this kind of safety practice, but there are many more important things to learn.