My FreeBSD machine shutted down with the following logs;
WARNING: system temperature too high, shutting down soon! acpi_tz0: WARNING - current temperature (84.0C) exceeds safe limits
"sysctl hw.acpi.thermal.tz0.passive_cooling" showed zero.
The next configuration in /etc/sysctl.conf can stop this problem.
hw.acpi.thermal.user_override=1 hw.acpi.thermal.tz0._PSV=75C hw.acpi.thermal.tz0.passive_cooling=1
I found that dev.cpu.0.freq decreased in high load.
$ sysctl dev.cpu.0.freq hw.acpi.thermal.tz0.temperature dev.cpu.0.freq: 1000 hw.acpi.thermal.tz0.temperature: 75.0C
dev.cpu.0.freq had been always 1400 without the above configuration.