How far away is lightning by the flash-to-bang method?

Count the seconds between seeing the flash and hearing thunder. Sound travels about one mile every 5 seconds and one kilometre every 3 seconds, so 15 seconds means roughly 3 miles or 5 kilometres.

What is the 30/30 lightning rule?

If flash-to-bang is 30 seconds or less (about 6 miles / 10 km), get inside a substantial building or hard-top vehicle immediately. Stay sheltered until 30 minutes after you hear the LAST thunder — every new boom restarts the clock.

Is it safe under a tree during a thunderstorm?

No. Isolated and tall trees are among the deadliest places to stand. Avoid the tallest objects, ridges, open meadows, water and metal fences; keep at least 15 ft (4.5 m) from trunks and, as a last resort, use a low thicket shorter than the surroundings.

Can lightning strike when it is not raining?

Yes. Bolts from the blue strike 10-15 miles ahead of the rain shaft, and lightning can occur before the rain arrives or after it ends. If you can hear thunder you are within striking distance.

What is the lightning crouch and when should I use it?

Only as a last resort with no real shelter: crouch low with feet together on an insulating pad or rope, head down and hands over ears, while the group spreads 15-20 ft apart. A hard-top vehicle or fully enclosed building is always the correct choice.

Lightning Safety Timer闪电安全计时器

Flash-to-bang distance, the 30/30 rule and a live 30-minute all-clear countdown after the last thunder. 闪光雷声测距、30/30 规则，以及末次雷声后实时 30 分钟解除倒计时。

🧭 Weather & Navigation天气与导航求救 ⚡ Thunderstorm · 30/30 rule雷暴 · 30/30 规则 📅 Updated Oct 20262026 年 10 月更新

How the lightning timer works

Light arrives essentially instantly while thunder takes roughly five seconds per mile. That single fact, applied honestly, removes the guesswork from when to leave a summit and when it is finally safe to come out.

Flash to bang: the distance

Start counting when a flash appears and stop at the first thunder. Miles = seconds ÷ 5 and kilometres = seconds ÷ 3, so a 15-second gap means the strike was about 3 miles (5 km) away. Count every visible flash; distance estimates for individual bolts vary, and the nearest strike is the one that matters. You do not need rain — lightning frequently strikes 10–15 miles beyond the rain shaft, and hearing thunder means you are already inside striking distance.

The 30/30 rule

The first “30” is an action threshold: at 30 seconds or less (roughly 6 miles / 10 km), move immediately to a substantial, fully enclosed building or a hard-top metal-roof vehicle with the windows up. Tents, picnic shelters, cave mouths, porches, convertibles and golf carts are not safe. The second “30” is a waiting rule: remain sheltered until 30 minutes after the LAST thunder. The built-in timer stores the moment you log each thunderclap and runs a live mm:ss countdown; a new clap restarts it, and surviving a reload lets you see the time remaining rather than guessing.

If the storm catches you high

Leave summits, ridges, open meadows, water, wet ropes, metal fencing and poles well before the 30-second threshold. Never shelter under the tallest tree; stay at least 15 ft (4.5 m) from trunks and prefer a low stand of trees shorter than everything around them. Spread the group 15–20 ft (4.5–6 m) apart so one ground current cannot drop the whole party. The lightning crouch — feet together, crouch low, hands over ears, standing on a pad or rope — is a last resort, not a plan. In a car, keep windows up, hands in your lap and away from metal frames, wired devices and charging cables.

闪电计时器原理

光几乎瞬间到达，雷声每英里约走 5 秒。只要诚实运用这一条，就能消除“何时下撤、何时能出来”的猜测。

闪光到雷声：距离换算

看到闪光开始数、听到第一声雷停止。英里 = 秒数 ÷ 5；公里 = 秒数 ÷ 3，所以 15 秒间隔约等于 3 英里（5 公里）。每一道可见闪电都要数：单次雷击距离会波动，最近的那一次才关键。没有下雨也要数——闪电常打到雨幕前方 10–15 英里，能听到雷声就说明已在可击中距离内。

30/30 规则

第一个“30”是行动阈值：声光差 ≤ 30 秒（约 6 英里 / 10 公里）时，立即进入坚固封闭建筑，或车窗全关的硬顶金属顶汽车。帐篷、凉亭、洞口、门廊、敞篷车、高尔夫车都不安全。第二个“30”是等待规则：在最后一声雷之后继续躲避 30 分钟。内置计时器会保存你每次记录雷声的时刻并实时 mm:ss 倒计时；新雷一响重新计时；刷新页面后倒计时仍在，不必靠猜。

被风暴堵在高处怎么办

远在 30 秒阈值到来之前，就离开山顶、山脊、开阔草甸、水面、湿绳索、金属围栏与杆。绝不在最高的树下避雨；距任何树干至少 4.5 米（15 英尺），优先选周围有更高物的低矮树丛。队员间隔拉开 4.5–6 米（15–20 英尺），避免一次地面电流同时放倒全队。避雷姿势（双脚并拢、蹲低、掩耳、垫在睡垫或绳索上）只是最后手段，不是计划。车内时升窗、双手放腿上，远离金属门框、有线设备与充电线。

Frequently asked questions常见问题

Why divide by 5 and by 3 for the same storm?为什么同一场雷暴要分别除以 5 和 3？

Sound travels about 1,100 ft (340 m) per second, which works out to one mile per 5 seconds and one kilometre per 3 seconds. The two answers describe the same distance in different units.声速约 340 米/秒，折算为每 5 秒 1 英里、每 3 秒 1 公里。两个答案只是同一距离的不同单位。

A car is safe in a storm — is the rubber tyre myth real?车里安全是因为橡胶轮胎绝缘吗？

No. A fully closed hard-top vehicle works because its metal shell routes current around the occupants (a Faraday-like effect), not the tyres. Keep windows up and avoid touching conductive parts. Convertibles offer no such protection.不是。完全封闭的硬顶车安全，是因为金属壳体把电流导向乘员四周（类法拉第效应），与轮胎无关。记得关窗且不触碰导电部件；敞篷车没有这种保护。

Is the lightning crouch a recommended position?避雷姿势是推荐姿势吗？

It is a last resort when no real shelter exists: feet together, crouch low on a pad or rope, head down, hands over ears, with the party 15-20 ft apart. Authorities emphasise it does not make open ground safe — leaving risky terrain early does.它只是没有真正避险所时的最后手段：双脚并拢、蹲在睡垫或绳索上、低头掩耳，队员间隔 4.5–6 米。权威机构强调它不能让开阔地变安全——提前离开危险地形才有用。

Do I really wait 30 minutes after the last thunder?最后一声雷后真的要等 30 分钟吗？

Yes. Roughly one third of lightning fatalities happen after the storm appears to have passed, often under blue sky. Every new thunderclap restarts the 30-minute timer, even after the rain stops.是的。约三分之一雷击死亡发生在风暴看似过去之后，且常出现在蓝天下。哪怕雨已停，每响一声新雷都要把 30 分钟重新计时。

Is it safe in a tent or under a picnic shelter?在帐篷或凉亭里安全吗？

Neither is lightning-safe. Tents and open-sided shelters often sit under trees or on exposed ground and their poles conduct. Use them for rain only after the 30/30 rule says the storm is genuinely gone.都不能防雷。帐篷与开放式凉亭常在树下或开阔地，帐杆还会导电。只有当 30/30 规则确认风暴真正离开后，才把它们当作避雨处。