It should not be dangerous to use 100% of available CPU resources. If it is, that is a design defect in the system.
It absolutely is a cooling issue. If it is “dangerous” to fully use the CPU, then the CPU is not getting cooled enough. That is a system problem, not software problem.
Anyway – the solution for you is to down-clock the CPU 20% in the BIOS. Then using 100% of available CPU (which is what software should absolutely do) will run the CPU at 80% load and you’ll get what you want.
Or, to put it another way: You’ll be configuring your CPU to operate within the TDP that your cooling solution can actually support.