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IEC TR 62713: Lightning Safety Procedures Outside a Structure
Life-Saving Knowledge: IEC TR 62713, prepared by IEC TC 81 (Lightning Protection), is a unique technical report that bridges the gap between structural lightning protection standards (IEC 62305 series) and practical personal safety measures for people caught outdoors during thunderstorms. It provides evidence-based guidance for reducing the risk of lightning injury when no protected structure is available.
1. Understanding Lightning Damage Mechanisms
1.1 How Lightning Injures Human Beings
The report identifies five primary mechanisms through which lightning causes injury to humans. Understanding these mechanisms is essential for developing effective protection strategies.
| Mechanism | Description | Injury Severity | Risk Factor |
|---|---|---|---|
| Direct Strike | Lightning directly hits the victim’s body, typically the head or shoulders. This is the most dangerous scenario as the full lightning current passes through the body. | Extremely High (often fatal) | Being the tallest object in an open area |
| Side Flash | Lightning strikes a nearby object (tree, pole, building) and a portion of the current jumps (arcs) from that object to the person standing nearby. | Very High | Standing close to tall isolated objects |
| Touch Voltage | The victim touches an object that has been struck by lightning or is conducting lightning current. The potential difference between the object and ground drives current through the body. | High | Touching metallic structures during a storm |
| Step Voltage | Lightning current spreading through the ground creates a potential gradient. The voltage difference between the victim’s feet drives current up one leg and down the other, potentially through the heart. | Moderate to High | Walking or standing with feet apart near strike point |
| Upward Streamer | An upward discharge from the victim’s body (or from the ground near them) connects with the downward lightning leader, creating a partial current path. | Variable | Being in an area with high electric field enhancement |
Critical Safety Data: Worldwide, lightning kills approximately 24,000 people annually and injures 240,000 more. Most deaths occur outdoors, and crucially, many victims survive if immediate first aid — particularly cardiopulmonary resuscitation (CPR) — is administered promptly.
1.2 Physiological Effects of Lightning Strike
The human body is poorly equipped to handle the massive electrical current delivered by a lightning strike — typically 30,000 amperes at 300 million volts in a fraction of a millisecond. The report details the following injury categories: cardiac arrest (the most common cause of lightning fatality), neurological damage including memory loss and peripheral neuropathy, burns ranging from superficial Lichtenberg figures (fern-like patterns on the skin) to deep thermal burns at entry/exit points, and blunt trauma from the explosive shockwave or from being thrown by muscle contractions.
2. Practical Safety Procedures for Outdoor Scenarios
2.1 Risk Detection and Safe Locations
The report provides clear criteria for detecting lightning risk. The 30/30 rule is a fundamental guideline: seek shelter when the time between seeing lightning and hearing thunder is 30 seconds or less (indicating the storm is within 10 km / 6 miles), and remain sheltered for at least 30 minutes after the last thunderclap. Safe locations include large enclosed buildings with electrical and plumbing systems (which provide a path for lightning current to ground) and fully enclosed metal-topped vehicles (which act as Faraday cages, channeling current around the occupants).
Engineering Insight: A car acts as an effective Faraday cage because the lightning current flows through the vehicle’s conductive outer shell, around the occupants, and into the ground through the tires (which flash over at the high voltage). The vehicle’s internal electrical systems may be damaged, but occupants remain protected.
2.2 Scenario-Specific Guidance
| Scenario | Recommended Action | Common Mistakes |
|---|---|---|
| Open fields / sports grounds | Leave immediately; avoid being the tallest object; crouch low with feet together, hands over ears, minimizing contact with the ground. | Lying flat on the ground (increases step voltage exposure) |
| Under isolated trees | Stay at least 10 m away from the trunk. Trees attract lightning and side flash is a major risk. | Seeking shelter under the tallest tree in the area |
| In a car | Stay inside with windows closed. Avoid touching metal parts. The vehicle provides Faraday cage protection. | Getting out of the car or touching door frames |
| Camping / tents | Do not use a tent as lightning shelter. Avoid ridge lines and hilltops. Go to a hard-topped vehicle or substantial building. | Staying in a tent thinking fabric provides insulation |
| Mountainous terrain | Descend from peaks and ridges. Stay away from cliff faces and overhangs. Crouch on insulating material if available. | Taking shelter in shallow caves or under rock overhangs |
| On water (swimming, boats) | Get out of water immediately. Small boats should head to shore. On larger boats, go inside the cabin and avoid metal. | Staying in the water (water conducts lightning current efficiently) |
| Open-air festivals | Follow event emergency plan. Avoid large open spaces. Do not seek shelter under temporary structures or umbrellas. | Huddling together under a single canopy or tree |
| Outdoor sports | Stop play immediately. Leave the field, course, or court. Metal equipment (golf clubs, bicycles, fences) increases risk. | Continuing play or holding metal sports equipment |
Important Clarification: The “lightning crouch” (sitting or crouching with feet together, arms wrapped around knees) does not attract or repel lightning. Its purpose is to minimize your height profile and reduce step voltage risk by keeping your feet as close together as possible. It remains a last-resort measure, not a substitute for proper shelter.
3. First Aid and Medical Response
The report dedicates significant attention to post-strike response. Victims of lightning strike do not carry an electrical charge and can be safely touched immediately. Cardiopulmonary resuscitation (CPR) is the most critical intervention — lightning victims often suffer cardiac arrest but may have a better chance of survival than other cardiac arrest patients if CPR is started promptly, because the respiratory system may remain functioning, providing oxygenated blood for the heart to circulate. Multiple victims should be triaged using reverse triage principles: those who appear unresponsive (in cardiac arrest) should be treated first, as those who are conscious and moving are likely to survive.
Life-Saving Protocol: The 30/30/30 rule for emergency response: within 30 seconds of the victim collapsing, begin CPR; within 30 minutes, the victim should be in advanced medical care; and the rescuer should ensure their own safety (30 m from any strike-vulnerable object).
4. Engineering and Design Implications
For engineers involved in lightning protection system design, this report provides essential context for the human safety dimension of the IEC 62305 series. Key takeaways include: early warning systems (lightning detection networks) should be integrated into outdoor venue designs; signage for safe refuge locations should be standard in parks, sports facilities, and campsites; and educational materials based on this technical report can significantly reduce injury rates when incorporated into public safety campaigns.
5. Frequently Asked Questions
Q1: Is it true that lightning never strikes the same place twice?
A: No, this is a myth. Lightning frequently strikes the same location repeatedly — tall buildings, towers, and prominent trees can be struck dozens of times per year. The Empire State Building is struck approximately 25 times annually.
A: No, this is a myth. Lightning frequently strikes the same location repeatedly — tall buildings, towers, and prominent trees can be struck dozens of times per year. The Empire State Building is struck approximately 25 times annually.
Q2: Do rubber shoes protect against lightning step voltage?
A: No. The voltage gradient in the ground during a nearby lightning strike is far too high for any conventional footwear to provide meaningful insulation. Keeping feet close together is the only practical way to reduce step voltage risk when caught outdoors.
A: No. The voltage gradient in the ground during a nearby lightning strike is far too high for any conventional footwear to provide meaningful insulation. Keeping feet close together is the only practical way to reduce step voltage risk when caught outdoors.
Q3: What is the “30/30” lightning safety rule?
A: Seek shelter when the time between lightning flash and thunder is 30 seconds or less (storm within ~10 km), and wait at least 30 minutes after the last thunder before leaving shelter. This rule is backed by statistical analysis of lightning injury data.
A: Seek shelter when the time between lightning flash and thunder is 30 seconds or less (storm within ~10 km), and wait at least 30 minutes after the last thunder before leaving shelter. This rule is backed by statistical analysis of lightning injury data.
Q4: Can you use a mobile phone during a thunderstorm?
A: Yes, using a mobile phone (cordless) is safe during a thunderstorm. However, corded landline phones should NOT be used, as they provide a direct conductive path for lightning current into the building’s electrical system and into the user’s ear and hand.
A: Yes, using a mobile phone (cordless) is safe during a thunderstorm. However, corded landline phones should NOT be used, as they provide a direct conductive path for lightning current into the building’s electrical system and into the user’s ear and hand.
