7.5 Electric Shock: Prevention, Rescue and Emergency Response

7.5 Electric Shock: Prevention, Rescue and Emergency Response

ACMA Exam Focus: Syllabus items 10.1, 10.11, 10.12 and 10.13. You must recall that high voltages and high currents are dangerous, that the first action at an electrical accident is to safely switch off the power, that a casualty must not be touched until the power is off, and that emergency services must be called immediately and CPR may be needed.

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1. Current Injures, Not Voltage Alone

Voltage is what pushes current through you; current is what does the damage. How much current flows is set by Ohm's law and by your body resistance at that moment.

Body resistance is the variable that turns a survivable event into a fatal one. Dry, unbroken skin might present 10 kilohms to 100 kilohms hand to hand, giving a few milliamps at 230 V. Wet, sweaty, cut or callus-free skin — or a hand on a mast in the rain at a field day — can fall to around 1 kilohm or less. At 1 kilohm, 230 V drives about 230 mA, several times the current needed to cause ventricular fibrillation.

Three further points the exam expects you to have internalised:

• Path matters. Hand-to-hand and hand-to-foot paths cross the chest and the heart. A shock from fingertip to fingertip of the same hand is far less likely to be fatal.
• Mains frequency is particularly dangerous. 50 Hz sits in the range most effective at inducing ventricular fibrillation.
• Low current rating does not mean safe. A power supply rated at only 100 mA can still deliver far more than the lethal current. The supply's rating limits what it will provide continuously, not what it will push through you.

That is why syllabus 10.1 pairs them: high voltages and high currents are both dangerous. In an amateur station the two everyday hazards are the 230 V mains and the several-hundred-volt to multi-kilovolt HT rails inside valve amplifiers and transmitters.

2. Preventing Shock in the First Place

• Switch off, unplug and prove dead before working inside equipment, and observe the high-voltage capacitor discharge procedure covered earlier in this chapter. A switch is not an isolation device — pull the plug.
• One-hand rule. When measurements must be made on energised equipment, keep the other hand in a pocket or behind your back so no current path exists across the chest.
• Never work alone on equipment with dangerous voltages present. Someone must be able to isolate the supply and raise the alarm.
• Insulated tools, insulated-handle screwdrivers, and probes rated for the voltage being measured.
• Remove rings, metal watch bands, bracelets and neck chains, wear dry shoes, and stand on a dry rubber mat rather than a damp concrete floor.
• Refit covers and never defeat interlocks. An interlock defeated for testing is an interlock left defeated.
• RCD protection on the shack circuit, tested regularly.
• Do not work tired, rushed, or after alcohol. Almost every serious shack accident report contains one of those three.

3. RF Burns

RF energy causes a different injury. Radio-frequency current does not stimulate nerves and muscles the way mains frequency does, so there is little of the warning tingle; instead it heats tissue directly and produces deep, slow-healing burns that look small at the surface while destroying tissue underneath. They are painful, prone to infection, and often need medical treatment.

The classic causes are touching an antenna, an open-wire feeder, a loading coil, or an unterminated feedline while transmitting, and adjusting an antenna tuner with a hand near the coil. Prevention: position or fence antennas so they cannot be touched by anyone during transmission, never handle a feedline or antenna while the transmitter is keyed, use a dummy load for testing, and remember that a small neon lamp brought near a live feedline will glow — a cheap way to check before you grab.

4. The Emergency Response Sequence (10.11 to 10.13)

Learn this order. The examiner tests it directly, and rescuers who get it wrong become the second casualty.

1. Switch off the power — first, and before anything else. Operate the station master switch, the switchboard circuit breaker or main switch, or pull the plug. Removing the hazard is the D for Danger in DRSABCD.
2. Do not touch the casualty while they may still be in contact with a live conductor. Current flowing through them will flow through you, and the let-go effect means they may be gripping the conductor and unable to release it.
3. If the power cannot be switched off, separate the casualty from the supply using a dry, non-conductive object — a wooden broom handle, a dry length of timber, a plastic chair, a dry rope — while standing on dry insulating material. Never use anything metallic, wet or damp.
4. Send for help: call Triple Zero (000) and ask for an ambulance. Give the address clearly and say that it is an electric shock. If someone else is present, send them to call while you attend to the casualty, and ask them to fetch a defibrillator if one is available nearby.
5. Check response and breathing. If the casualty is unresponsive and not breathing normally, begin CPR immediately and continue until the ambulance arrives or the casualty recovers.
6. Apply an AED as soon as one is available and follow its voice prompts. Electric shock frequently causes ventricular fibrillation, which is exactly what a defibrillator treats.

Australian first aid follows the Australian Resuscitation Council's DRSABCD action plan: Danger, Response, Send for help, Airway, Breathing, CPR, Defibrillation. Current ARC guidance for adult CPR is 30 chest compressions to 2 rescue breaths at a rate of 100 to 120 compressions per minute; compression-only CPR is far better than no CPR if you are unable or unwilling to give breaths. Do not learn resuscitation from a study guide. Complete an accredited first-aid and CPR course, refresh it regularly, and encourage your club to run one — CPR is a physical skill, and the exam item exists because amateurs work alone with lethal voltages.

5. After the Incident

• Every electric-shock casualty needs medical assessment, even if they say they feel fine. Shock can cause delayed cardiac arrhythmia hours afterwards, and current passing through the body produces deep internal burns along its path with only small entry and exit marks visible. Muscle damage and the after-effects of a fall are also common.
• Treat surface burns by cooling with running water; do not apply creams or break blisters.
• Do not re-energise the circuit until the fault has been found and rectified by a competent person, and quarantine the faulty equipment with a tag so nobody else plugs it in.
• Serious electric shock incidents are generally notifiable to the state or territory electrical safety or work health and safety regulator. If the incident happened at a club station or workplace, check and follow the notification requirements that apply in your jurisdiction.
• Debrief afterwards and fix the root cause: the missing cover, the defeated interlock, the habit of working alone.