Author Topic: The Silent Killer  (Read 1726 times)


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The Silent Killer
« on: September 23, 2013, 02:44:30 14:44 »
Well as John has gone to the efforts of developing the structure of the forum it's only good manners to fill it isn't it?  :)

When I started my professional education at technical college the first week was an intensive first aid course with the emphasis on issues arising from exposure to electrical shock and burns, the symptoms from exposure to all levels of voltage and current that found various paths through and over the human body, the care and treatment of the effects of exposure and so on and so forth…

This was the first subject we covered, In all the five senses we humans possess, there’s only one of those senses capable of detecting the presence of an electro motive force, electricity, you can’t see it, smell it taste it or hear it but we can touch it, and in case you needed confirmation, touching it is at the very least a painful experience and dependent upon a number of variables, can be fatal. 

The threshold at which an electric shock is more likely to prove fatal in the average human adult, children and the vulnerable are more susceptible, is a shock with a magnitude of 35mA and greater fault current, an electric shock under 35mA will cause muscular expansion, this is where victims speak of ‘being thrown across a room or off ladders and scaffolds’ where in fact they weren’t thrown, they jumped and pushed themselves involuntarily due to the effects of the electric shock.

Above 35mA and the effect on the human body is reversed, this causes muscular contraction and if you’re unlucky enough to have the fault path channelled from one hand or arm via your chest to the other side, then there is a high probability this will cause breathing difficulties with your lungs involuntarily contracting and ventricular fibrillation, cardiac arrest where you will have 90 seconds for someone to defibrillate before death.  And as you generally work with your hands more often than you do with your feet, unless you’re an ape  :) the chances of that fault path moving through your chest are pretty high.

It is this specific threshold of 35mA that protective devices were first introduced to interrupt power supplies upon the detection of a fault current of 30mA and above, so regardless of whether legislation exists or not, and it actually does, isn’t it just common sense that you should want to protect yourself from an electric shock with the installation of a Residual Current Device rated at 30mA or less?

Especially if you use the cheap and cheerful Chinese submersible! So the next time you pull it out of the fish tank by the supply flex while it is still live and attempt to clean the gunk from the filter casing or delve into the water to stick it back to the floor because you accidentally knocked it free when brushing all the collecting fish waste out of the corners of your fish tanks, you’ll be able to do it next time with the added confidence that you’ll be better protected from electric shock when that resin eventually breaks down and those nasty little currents start leaking out into the water  :) and let’s not forget about the fish, 2 or 3mA is all it will take to prepare them for the dinner plate.