The cheaper single tube dosimeters will max out and saturate at radiation levels far below those that are immediately harmful to human health. (This was the source of the famous "3.6 roentgen per hour, not great, not terrible" meme-- he was looking at a meter that was reading off-scale high at 0.001 R/s)
If you're buying a dosimeter with the threat in nuclear war in mind, check the specs for maximum readings.
Quote from HBO's Chernobyl, the dramatisization of Anatoly Dyatlov: https://knowyourmeme.com/memes/anatoly-dyatlov
A more balanced view of him: https://www.rbth.com/history/330525-anatoly-dyatlov-chernoby... and https://www.history.com/news/chernobyl-nuclear-disaster-7-pe...
Aside: all of us, even the most competent engineers, can deny what is happening or make bad calls during an emergency, especially where everything is unknown during the initial stages. It takes very good training to teach us to make better emergency decisions - e.g. firefighter's training, and some military. Beware of selection bias in repeated deadly situations.