page under construction.....heres Sunset and cloud drama over the M25 in the meantime.... 

Electrical fires and Electrical shocks 

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 We have removed countless electric shock and fire risks from properties over the years, recorded with thousands of photos and in some cases, the remains of burnt out products. See a HSE report into electric accident case studies. 

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 We have written a report on Electrical fatality and injury rate in the USA, compared with UK, quite interesting and surprising conclusions.

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  Around 30,000 fires occur every year in domestic property alone in the UK with almost 30% of those directly caused by electrical issues, for example an incorrectly rated protective device . EICR's reduce risks (see service page).

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 Faulty electrical items, such as washing machines, microwaves, tumble dryers etc led to 6,000 fires during 2011 in the UK. A faulty fridge was initial cause of Grenfell Tower fire tragedy. PAT or Portable Appliance Testing also helps reduce risks (see service page).

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 Persons receive electric shocks every hour of the day in the UK. It either causes a  tingling, muscle lock, serious injury or death, depending on various facts of fundamental physics and biology.

 

  The USA suffers around 10,000 injuries a year, half of which were life changing events (such as loss of a limb) and 400 fatalities, with another 200 electrical fire related fatalities. Currently we don't have accurate figures for the UK, although per head of population, its a lower rate.

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 The human body operates on a tiny, tiny fraction of a volt  (around 0.03V or 30 milli volts), using a electro-chemical process, so when you bump your toe for example, that message gets transferred to your brain at around 150 mph, using chemical, electrical sort of relay system. Electricity on the national grid, travels at close to the speed of light (around 670,000,000 mph).

   Yes, you guessed it, if you wired a bright red light onto the moon, there would be a 4-5 second delay, between switching it on and seeing it ( a little over 2 s there, a little under 2s back..light speed does have the upper hand, just).

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 Basic physics tells us, as the voltage increases, its able to overcome more resistance, and so 'drive' more current. As a persons electrical resistance to earth lowers, they become more vulnerable. Volts are 'push force'. Amps do the actual work. For example a 100 watt bulb has a resistance of around 530 ohms . 240 volts / 530 ohms = 0.45 Amps or 450 mA. 

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     Regarding amps (the work horse) and an otherwise healthy adult human:

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• 0.001 of an Amp or (1 milli amp or mA) can be felt as a tingle

• 0.01A or  10 mA  hurts, might cause muscle lock

• 0.02A or  20 mA muscle lock and impaired breathing.

• 0.05A  or 50mA causes the heart to go out of rhythm, called Ventricular Fibrillation, leading to risk of Sudden Cardiac Death (SCD) 

• larger currents ( if they don't go through the heart ) lead to burns, scarring, CNS damage etc.

• these figures are approximate and vary depending on individual circumstances, Ventricular Fibrillation can happen at 30mA for example.

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  During direct fault condition (pscc)a UK single phase, 240V AC system can and often does reach 3,000 amps and up to10,000 centigrade (vaporising metal), in a tiny fraction of a second, causing a correctly installed protective device to activate in around 10 milli seconds (mS), shutting down the power.

   

 Upstream from UK properties, the pscc is massively higher, hence a fault here causes events like a man hole cover to be blown off and a notable fire. click here

   

 Commercial electrics that run on 3 phase (420 volts) might have MCB's (miniature circuit breaker) that are  required to withstand up to 16,000 amps (16kA) under direct fault conditions (ie almost zero resistance) [ 420 volts / 0.03ohms  = 14,000 amps for example]

 

 Anyhow, the perhaps more dangerous situation is more insidious. For example, if your standing on a metal bath, changing a bulb on a bathroom light and receive a shock. 

 

 If for example your body  has an estimated lowered resistance of 4000 ohms to earth, as your feet are damp, Ohms law tells us that 240 / 4000 =  0.06 Amps or    60 mA. 

 Strong enough to lock your muscles and then cause Ventricular Fibrillation , within seconds, leading to risk of SCD.

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 It is paradoxically not anywhere near enough current to trip the fuse or MCB* so the electric shock event might continue for an extended length of time and create serious risks to first responders for example, if correct electrical isolation procedures are not followed.

 

 Bathrooms are electrically dangerous places and account for a lot of electric shock events across the UK and the world. This is one reason why bathrooms are considered one of many 'special locations' in regard to UK electrical regulations  (section 701 of BS:7671)

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 For arguments sake, if a 30 mA and correctly operational RCD was protecting that circuit, I would expect it to trip in between 20 and 80 mS, (with a 60mA fault to earth), scary but life saving.

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  RCD's do fail, the regulations stipulate not to rely on RCD's as sole means of protection : normal requirements of BS:7671 apply. They are very delicate items of equipment : high humidity, knocks, surge voltages etc can render them faulty.

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   * a correctly operational BS:60898, 6 amp 'type B' MCB Will not consider tripping until around 9 amps (9,000 mA) is reached and will then take 15 minutes. 20 amps would cause a trip in 30 seconds. 30 amps would cause a 0.1 or 10 mS trip.  according to Fig3.4 of BS:7671.  Primary purpose of an MCB and similar protective devices, is to protect the circuit from electrical fire. 

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