1986 年爆炸的切尔诺贝利反应炉外覆有一座巨大的围阻结构，该结构于 2016 年安装。2025 年 2 月，一次无人机袭击在其外壳上打出约 15 平方米的破洞；修复仅为部分，国际原子能机构（IAEA）表示其屏蔽能力已受损，但周边辐射水准迄今未见改变。历史案例也显示异常能被迅速察觉：1986 年事故后，瑞典东部的监测器在约两天后就侦测到异常辐射。

背景辐射通常以「微希沃特/小时」监测，并会随天气与地理条件而波动。香港在 2023 年因豪雨把氡的衰变产物从空中洗落到地面，使读数在约 0.06–0.3 µSv/h 的范围内变动，常见水准约在 0.1 µSv/h 左右。2009 年西班牙北部的强风暴引发氡相关辐射尖峰，甚至足以触发巴斯克地区伽玛监测网的误报；Safecast 志工也观察到同一条街上读数显著不同，以及沿海潮汐造成的轻微变化。

监测能力已从以封闭的政府系统为主，扩展为政府、研究与 DIY 网路并存。福岛事故（2011）后，民间需求上升；Safecast 目前汇集全球超过 5,000 台探测器资料，而部分国家也把国家监测资料以近即时方式公开，IAEA 的全球地图更新延迟从数分钟到约一小时不等。该地图上红色可代表 ≥1,000 µSv/h（福岛危机高峰曾出现此量级），但不少警报属低风险来源，例如机场安检：伦敦希斯洛在 2022 年曾拦到含少量铀的货物，或是来自医疗同位素。

Chornobyl’s reactor, which exploded in 1986, is covered by a huge confinement structure installed in 2016. In February 2025 a drone strike punched a ~15 m² hole; repairs are partial, and the IAEA says shielding is compromised though local radiation levels have not yet changed. Past disasters showed how fast anomalies surface: after Chornobyl, monitors in eastern Sweden detected unusual radiation about two days later.

Background radiation is tracked in microsieverts per hour and can swing with weather and geography. Hong Kong’s 2023 heavy rains washed radon decay products down, pushing readings within roughly 0.06–0.3 µSv/h around a usual ~0.1 µSv/h. Storm-driven radon spikes in northern Spain (2009) even triggered false alarms in the Basque Country gamma network; Safecast volunteers also observed sharp street-to-street variation and small tidal effects on coasts.

Monitoring has shifted from mostly closed government systems to mixed public and DIY networks. After Fukushima (2011), demand surged; Safecast now aggregates data from 5,000+ detectors worldwide, while some national systems publish near‑real‑time feeds and the IAEA’s map updates within minutes to about an hour. On that map, red can indicate ≥1,000 µSv/h—levels seen at Fukushima’s peak—yet many alerts are benign, such as airport screening (Heathrow in 2022 flagged a small uranium shipment) or medical isotopes.