Occupational health and safety
This topic is not an administrative formality: it is the one that decides whether someone gets home safe. Electricity gives no warning, cannot be seen and does not forgive improvisation, and most serious accidents happen during routine tasks carried out by experienced people.
01What current does to the body
What does the damage is not the voltage but the current, how long it flows and where. Voltage matters because it determines that current against the body's resistance, which ranges from about 1000 Ω with dry skin to less than 500 Ω with wet hands.
| Current (50 Hz) | Effect |
|---|---|
| 0.5 to 1 mA | Threshold of perception: barely a tingle. |
| 5 mA | Unpleasant sensation. Sudden reaction: the danger becomes the blow or the fall. |
| 10 to 15 mA | Tetanization: the muscles contract and the person cannot let go of the conductor. |
| 25 to 30 mA | Diaphragm contraction: breathing becomes difficult. Dangerous if it lasts. |
| 50 mA and above | Risk of ventricular fibrillation: the heart stops pumping. It is the usual cause of death by electric shock. |
| Amperes | Cardiac arrest and deep internal burns that look like little injury on the skin. |
- With dry hands (≈ 2000 Ω) and 220 V: I = 220/2000 = 110 mA. Far above the fibrillation threshold.
- With damp hands (≈ 800 Ω): I = 275 mA.
- With 24 V and 2000 Ω: I = 12 mA. It is felt and is unpleasant, but it is rarely lethal in dry conditions.
That is why industrial control circuits work at 24 V, and why the limits of safety extra-low voltage are 50 V AC and 120 V DC, and considerably lower in damp locations.
Right hand to left foot passes through the heart; hand to hand does too. Hence the habit of working with one hand only and the other in your pocket when something energized is nearby: if the current enters and leaves through the same hand, the damage is local.
02Direct and indirect contact
Touching a part that is normally live: a bare conductor, a terminal, a contactor contact.
It is prevented with insulation, enclosures, barriers, clearances and signage. The RCD is the last line of defense, not the first.
Touching a metal part that should not be live but is because of an insulation fault: a motor's enclosure, a machine's casing.
It is prevented with grounding plus an RCD, or with double insulation. It is the most treacherous case, because nothing looks different.
- Eliminate the hazard: work de-energized. It is the only measure that never fails.
- Substitute: use safety extra-low voltage wherever possible.
- Collective protection: enclosures, barriers, interlocks, grounding, RCDs.
- Signage and procedures: lockout, tagout, work permits.
- Personal protection: gloves, footwear, face shield. It is the last resort, not the first: it protects one person and only if it is used correctly.
03The five golden rules
| Step | What you do | Why |
|---|---|---|
| 1 | Disconnect all sources of voltage | Including the non-obvious ones: another supply, a generator set, a battery, a charged capacitor, energy stored in a spring or in compressed air. |
| 2 | Lock out and tag the disconnecting device | With your own lock and a tag with your name. This is LOTO (lockout/tagout): only the person who put the lock on removes it. If three people are working, there are three locks. |
| 3 | Verify the absence of voltage | With a suitable instrument, on all conductors, and testing the instrument before and after on a known source. |
| 4 | Ground and short-circuit | Mandatory in medium and high voltage: it protects against accidental reconnection or an induced voltage. |
| 5 | Delimit and mark off the area | So that no outsider enters or reconnects, and so that it is clear where the safe zone ends. |
Because “we already disconnected it, it must be dead.” The real cases that prove otherwise are always the same: the wrong switch was opened, the panel was mislabeled, another line feeds the same terminal, someone reconnected, or the instrument itself was faulty. Verifying takes twenty seconds. And the instrument must be verified too: a voltage tester with a dead battery shows nothing, exactly like a circuit with no voltage.
04The electric arc
It is the least known hazard and one of the worst. A short circuit in a panel can form an arc of thousands of degrees that vaporizes the copper, expands the air suddenly and throws molten metal. You do not need to touch anything: being nearby is enough.
- A tool that falls and bridges two busbars.
- An instrument on the wrong range —ammeter across a voltage— is the classic cause.
- A probe tip that slips.
- Operating a switch with a bolted fault downstream.
- Work de-energized: it eliminates the hazard completely.
- Insulated, full-handle tools with no exposed metal parts.
- An instrument of the correct category with original fuses.
- Cotton or flame-resistant clothing —never synthetic, which melts onto the skin— and a face shield when appropriate.
- Do not rest tools or instruments on the open panel.
05Other electronics workshop hazards
| Hazard | Where it appears | Measure |
|---|---|---|
| Thermal | Soldering iron at 350 °C, heat sinks, power resistors | Keep the iron in its stand at all times; warn others before leaving something hot on the bench. |
| Soldering fumes | The rosin flux in solder irritates the airways | Fume extractor or at least ventilation. It is not lead fume, but it still does harm. |
| Lead | Traditional tin-lead solder | No eating or drinking at the workstation; wash your hands when done. |
| Chemical | Ferric chloride, isopropyl alcohol, aerosols | Gloves, safety goggles, ventilation and disposal as special waste: it does not go down the sink. |
| Projectiles | A reversed electrolytic capacitor explodes; solder spatters | Safety goggles. It is the most common accident and the most avoidable. |
| Mechanical | Drill, PCB drilling machine, shear cutter | Clamp the workpiece, never hold it by hand; safety goggles; no loose clothing or dangling sleeves. |
| Noise | Compressors, motors, blowers | Hearing protection above 85 dB sustained. |
| Ergonomics and eyesight | Hours of fine soldering and screen work | Good lighting, magnifier, bench height, breaks. |
06Argentine regulatory framework
| Regulation | What it establishes |
|---|---|
| Ley 19,587 (Occupational Health and Safety Law) | The framework law: obligations of the employer and the worker. |
| Decreto 351/79 | Its implementing regulation: conditions of workplaces, lighting, noise, electrical hazard, personal protection. |
| Ley 24,557 (Occupational Risks Law) | System of ART (occupational risk insurers), prevention and compensation. |
| AEA 90364 (Argentine Electrotechnical Association) | Regulation for the execution of electrical installations in buildings: the one the technician uses every day. |
| IRAM 10005 (Argentine Standards Institute) | Safety colors and signs: red for prohibition and fire, yellow for warning, green for rescue, blue for mandatory action. |
- The employer must provide safe conditions, protective equipment, training and written procedures.
- The worker must use the equipment, follow the procedures and report any unsafe condition detected.
- No one is obliged to perform a task under unsafe conditions. Refusing to work without lockout, without a verified instrument or without protection is not misconduct: it is complying with the regulations.
07If someone receives an electric shock
- Do not touch them. If they are still in contact, whoever touches them gets caught too.
- Cut the power: switch, circuit breaker, panel. If that is not possible, separate them with an insulating, dry object —a wooden stick, a plastic chair— while standing on insulating material.
- Call for help: 107, medical emergencies. Say that it is an electrical accident.
- Assess consciousness and breathing. If they are not breathing, start CPR and use the defibrillator if one is available.
- Always transport them to hospital, even if the person seems fine: a shock can cause heart rhythm disturbances hours later, and internal burns cannot be seen.
08In the lab
On a training panel, carry out the complete procedure with lock and tag, verifying with an instrument and testing the instrument before and after. Time it: it takes less than two minutes. Repeat it until you can do it without consulting the list.
Walk through the workshop with a checklist and note: extension cords in poor condition, plugs without ground pin, unlabeled panels, expired fire extinguishers, blocked exits, uninsulated tools, lack of safety goggles. Prioritize by risk and propose corrections. Audit again after two weeks.
Check the workshop's RCD with its test button and record the date on a log sheet. Discuss how often it should be done and who would be responsible in a workplace.
With a documented real case, reconstruct the sequence and identify at what point one of the five rules —or a collective protection— would have broken the chain. There is almost always more than one point where the accident could have been avoided.
09Common mistakes
| Unsafe practice | Why it is serious |
|---|---|
| “It’s only a minute, I won’t disconnect” | Most serious accidents happen during short, routine tasks. |
| Disconnecting without locking out | Anyone can reconnect without knowing someone is working. |
| Not verifying the absence of voltage | The panel may be mislabeled or fed from somewhere else. |
| Using the multimeter on its current range to measure voltage | A dead short and an electric arc. It is one of the most common causes of serious burns. |
| Instrument with an insufficient category rating | It cannot withstand the panel's transients: it explodes in your hand. |
| Working alone on energized installations | If something goes wrong, there is nobody to cut the power or to assist. |
| Rings, watches or metal bracelets | They concentrate current and heat: they cause very severe burns. |
| Synthetic clothing | In an arc, it melts onto the skin and greatly worsens the injury. |
| Bypassing a protective device “because it keeps tripping” | The protection trips for a reason. Bypassing it turns a fault into a fire. |
10Self-assessment
Which is more dangerous: voltage or current?
The current flowing through the body, together with the time and the path. Voltage matters because, against the body's resistance, it determines that current.
At what current can a person no longer let go of the conductor?
Around 10 to 15 mA AC: this is muscular tetanization. That is why the protection threshold of household RCDs is 30 mA and they act within milliseconds.
With 220 V and a body resistance of 1500 Ω, what current flows?
I = 220/1500 = 147 mA: far above the threshold of ventricular fibrillation.
What is the difference between direct and indirect contact?
Direct contact is touching a part that is normally live; indirect contact is touching an exposed metal part that became live through an insulation fault. The second is prevented with grounding plus an RCD.
List the five golden rules in order.
1) Disconnect all sources. 2) Lock out and tag. 3) Verify the absence of voltage. 4) Ground and short-circuit. 5) Delimit and mark off the area.
Why must you test the instrument before and after verifying?
Because a faulty instrument reads “no voltage” exactly like a circuit that is really disconnected. By testing it on a known source before and after, that confusion is ruled out.
What are lockout and tagout, and why does each person put on their own lock?
It means physically securing the disconnecting device with a lock and an identified tag. Each person puts on their own so that nobody can reconnect while anyone is still working: power comes back only when the last lock has been removed.
Why is it dangerous to wear synthetic clothing at a panel?
Because in an electric arc it melts and sticks to the skin, making the burn far worse. Cotton or certified flame-resistant clothing is used.
Which operator error is one of the main causes of electric arcs?
Measuring voltage with the multimeter on the current range: the probes become practically a short circuit and a full arc results.
What is the first thing NOT to do with someone who has been electrocuted?
Touch them. First the power is cut or they are separated with an insulating, dry object; then you call for help and assess them. And they must always be taken to hospital, even if they seem fine.