Cooling at subzero temperatures and the subsequent monitoring of humidity in the modern Si-based high-energy physics detectors are indispensable but challenging due to space, radiation and magnetic field issues. In this study, a group of relative humidity sensors have been tested for operation reaching high irradiation doses adequate to the inner sub-detectors during the HL-LHC operation. The sensors were exposed to the 24 GeV/s proton beam for a period of 33 days reaching the fluence of 3 x 1016 protons/cm2. The test has demonstrated sensors radiation tolerance at high doses and their ability to provide valid alerts to the detector control and safety systems in the event of any changes in humidity. The irradiation was conducted in a temperature- and humidity-controlled environment. Tested samples were placed in a specially designed cold box able to guarantee an ambient temperature of -20 oC. Throughout the entire test, the compressed dry air was used to keep low humidity levels (around 0 %rh) inside the cold box, and a 100 ppm pre-calibrated gas mixture was used to test the sensors responsiveness before and after the irradiation process. Additionally, an on-purpose designed signal conditioning unit was used to compensate for the cable parasitic effects.