追加：第 1 节第 41 条，上野外冰面前先打孔量厚度

2026-10-02。来自 issue #63（读者提议「尽量远离冰面，防止冰窟溺水」）。全书原来没有冰面条目，溺水只有第 1 节第 12 条（儿童近水、救生衣）和第 13 节第 25 条（看到有人溺水自己不下水），不算重复。追加在第 1 节末尾，没有插在中间。

和读者原稿的差别

原稿标 A。来源全是政府安全指南，没有研究算过照做能少死多少人，按分级规则改为 C。
原稿收益栏「严格遵守冰层安全厚度指南，可以规避绝大多数由冰面碎裂导致的意外坠冰事故」在五个来源里都找不到，删掉。
原稿把 10 厘米写成门槛。国内官方（中国气象局、北京市水务局、国家体育总局转载的中国体育报）一致写 15 厘米，标题按更严的国内口径写，10 厘米作为美加底线写在说人话和收益栏。
补了 DNR 原文「同一片水面厚薄差很多」，所以要边走边量，不是量一次就行。
原稿成本写「冰锥或卷尺」。打孔用冰钻或冰镩；冰锥在这里指落水自救用的一对带握柄尖钉（ice picks），条目里写明了是什么。
原稿来源【3】加拿大红十字会只给了域名，改用 CCOHS 页面里对红十字会建议的转述。来源【5】USACE 页面没有用上，条目里的数字都能在其余页面找到。

URL：https://www.dnr.state.mn.us/safety/ice/thickness.html（2026-10-02 带代理取到，页面标注更新于 2025-01-28）
原文：「Ice thickness guidelines for new, clear ice only. UNDER 4" Stay off 4" Ice fishing or other activities on foot」；「When a layer of snow melts and refreezes on top of lake ice, it creates white ice, only about half as strong as new, clear ice. Double the above thickness guidelines when traveling on white ice.」；「Ice is seldom the same thickness over a single body of water; it can be two feet thick in one place and one inch thick a few yards away.」

URL：https://www.dnr.state.mn.us/safety/ice/index.html
原文：「There is no such thing as 100 percent safe ice.」；「It may be a foot thick in one location and only an inch or two just a few feet away.」；「Ice formed over flowing water and currents is often dangerous. This is especially true near streams, bridges and culverts.」；「Also, ice near shore can be weaker than ice that is farther out.」
条目收益栏「这里一英尺厚，几英尺外只有一两英寸」取自这一页。

URL：https://www.dnr.state.mn.us/safety/ice/survival.html
原文：「Don't remove your winter clothing. Heavy clothes won't drag you down, but instead can trap air to provide warmth and flotation.」；「Turn toward the direction you came. That's probably the strongest ice.」；「Kick your feet and dig in your ice picks to work your way back onto the solid ice.」；「Lie flat on the ice once you are out and roll away from the hole」；「In moderate to severe cases of cold water hypothermia, you must seek medical attention.」
备注里的自救步骤取自这一页。

URL：https://www.weather.gov/safety/winter-ice-frost
原文：「For ice fishing, ice skating and walking, you need 4 inches or more of ice.」；「White or "snow" ice is only about half as strong as new, clear ice. Double these thickness guidelines when traveling on white ice.」

URL：https://www.ccohs.ca/oshanswers/hsprograms/work_ice.html
原文：「Essentially, there is no absolutely "safe" ice.」；「If walking or working on foot, minimum ice thickness must be at least 10 cm (4 inches) of clear, good quality ice」；「Canadian Red Cross recommends that ice thickness should be a minimum of: 15 cm (6 inches) for skating, walking or skiing in small groups 20 cm (almost 8 inches) for larger groups, such as skating parties」。

URL：https://swj.beijing.gov.cn/swdt/ztzl/fnsbaqztxc/fnszlxx/202412/t20241226_3973959.html
原文：「正规的天然冰场的冰面厚度需达到15厘米才能开放，并且之后一周气温持续保持在-8℃到1℃之间，在不出现大风天气的条件下冰场才能开放」；「常有钓友凿冰垂钓，凿开的冰洞很难再冻结，形成一个个"冰陷阱"」。