Safetyelectricshocks (unit301)

Definition: An electric shock is an unpleasant sensation produced by the response of nerves to the passage of electric current through the body.
Circuit Requirement: Shock only occurs when becoming part of a complete circuit between a source and earth ("No circuit - No shock").
Influencing Factors: Physiological impact depends on age, sex, general health condition, and moisture levels in the immediate environment.
Primary Physiological Dangers: Causes irregular cardiac rhythms (heart failure) and contact burns.

$0.5\,mA - 2\,mA$ (Threshold of Perception): The minimal current level detectable by human senses.
$2\,mA - 10\,mA$ (Pain / Let-Go Level): Painful sensation that intensifies with current; voluntary muscle release remains possible up to approximately $10\,mA$ .
$10\,mA - 25\,mA$ (Hold-On Level): Involuntary muscular cramping preventing release of live conductors; accompanied by increased blood pressure and breathing difficulties due to lung muscle contraction.
$25\,mA - 50\,mA$ (Throwing Level): Severe muscular contractions capable of throwing the body and fracturing bones; marked by high blood pressure and potential loss of consciousness from cardiac or respiratory failure.
$50\,mA$ (Lower Lethal Level): Fatal threshold causing severe contact burns and lethal heart failure (current level is less than what is required to power a laptop).

Direct Contact: Do not touch the casualty directly.
Alarm: Shout immediately for assistance.
De-energize: Turn off the power supply at the source whenever possible.
Physical Separation: If power cannot be isolated, pull the victim clear using non-conductive insulating items (such as a dry broom, scarf, wooden stick, or newspaper).
Medical Care: Summon emergency medical aid prior to starting cardiac massage or artificial respiration if the heart has stopped; treat burns and related trauma strictly within personal training limits.

Direct Contact: Touching conductive elements that are energized under normal operating conditions (such as drilling into concealed live electrical cabling).
Indirect Contact: Touching exposed conductive parts (such as metallic pipework) that are normally dead but become energized during an electrical fault (typically below $230\,V$ , though still dangerous).
Protective Bonding: Extraneous metallic services (gas and water) are bonded via $10\,mm^2$ main protective bonding conductors back to the consumer unit earth terminal ( $16\,mm^2$ main earthing conductor) to prevent voltage differentials in TN-S, TN-C-S, and TT supply systems.

Approved Voltage Indicator (AVI): Testing for dead must be conducted using a purpose-built AVI; neon test screwdrivers are strictly prohibited.
AVI Design Standards:
- Robust, flexible, sheathed rubber cables that protect against mechanical damage and prevent finger access if loosened.
- Integrated finger guards or barriers on both probes to prevent hand slippage.
- Insulated probe tips with maximum $4\,mm$ exposed metal (preferably $\le 2\,mm$ ).
- Leads protected by integrated High Breaking Capacity (HBC/HRC) fuses rated at $500\,mA$ .

Proving Unit: A dedicated DC voltage reference source used to verify that the AVI is operational immediately before and after testing.

Sequence of Execution:
- Step 1: Plan the job thoroughly.
- Step 2: Unplug any connected equipment.
- Step 3: Securely isolate the circuit or equipment.
- Step 4: Prove the test instrument against a known voltage source (proving unit).
- Step 5: Prove that the target circuit or equipment is dead.
- Step 6: Re-prove the test instrument against the proving unit to confirm it functioned correctly during testing.
- Step 7: Attach temporary earth leads if operational safety requires.
- Step 8: Post caution and warning notices on the isolation point.
- Step 9: Consider the necessity of additional safety precautions.
- Step 10: Ensure complete understanding of the job before commencing work.