System for determining a concentration of gas in a confined space, said system comprising: a first frequency generator for generating a first radio frequency signal; a first antenna electrically connected to said first frequency generator for transmitting the first RF signal across the confined space; a second antenna for receiving the first RF signal; a so-called second RF signal power detector for detecting the power of the first RF signal received at said second antenna characterized in that the system further comprising: a so-called first RF signal power detector for detecting the power of the first RF signal prior to transmission through the confined space; a so-called first comparator circuit in communication with said first and second RF signal power detectors (22, 28) for determining a concentration of oxygen in the confined space based on at least the power of the first RF signal prior to transmission through the confined space and the power of the first RF signal received by said second antenna; a second frequency generator for generating a second RF signal; a third antenna electrically connected to said second frequency generator for transmitting the second RF signal across the confined space; a fourth antenna for receiving the second RF signal; and a so-called sixth comparator circuit, wherein the sixth comparator circuit is in communication with said second frequency generator and said fourth antenna for determining a concentration of water vapor in the confined space based on at least the second RF signal prior to transmission through the confined space and the second RF signal received by said fourth antenna, wherein said first comparator circuit is in communication with said sixth comparator circuit for determining a concentration of water vapor in the confined space and determining a concentration of oxygen in the confined space based on at least the power signals corresponding to the first RF signal and the concentration of water vapor in the confined space. a first frequency generator for generating a first radio frequency signal; a first antenna electrically connected to said first frequency generator for transmitting the first RF signal across the confined space; a second antenna for receiving the first RF signal; a so-called second RF signal power detector for detecting the power of the first RF signal received at said second antenna characterized in that the system further comprising: a so-called first RF signal power detector for detecting the power of the first RF signal prior to transmission through the confined space; a so-called first comparator circuit in communication with said first and second RF signal power detectors (22, 28) for determining a concentration of oxygen in the confined space based on at least the power of the first RF signal prior to transmission through the confined space and the power of the first RF signal received by said second antenna; a second frequency generator for generating a second RF signal; a third antenna electrically connected to said second frequency generator for transmitting the second RF signal across the confined space; a fourth antenna for receiving the second RF signal; and a so-called sixth comparator circuit, wherein the sixth comparator circuit is in communication with said second frequency generator and said fourth antenna for determining a concentration of water vapor in the confined space based on at least the second RF signal prior to transmission through the confined space and the second RF signal received by said fourth antenna, wherein said first comparator circuit is in communication with said sixth comparator circuit for determining a concentration of water vapor in the confined space and determining a concentration of oxygen in the confined space based on at least the power signals corresponding to the first RF signal and the concentration of water vapor in the confined space.