The use of masks under strenuous conditions can be quite uncomfortable and laborious. It is hence imperative that the air inside the mask is as fresh as possible and the act of breathing is easy. This places limits on the total amount of “dead” volume due to the rebreathing of CO2 from the previous breath(s). This effect can cause the overall oxygen levels to fall and the wearer to breath more heavily and quickly to make up the difference. This leads to exhaustion, uncomfort and severe drops in cognitive performance which leads to mistakes, low morale and motivation. Measuring the CO2 levels is hence imperative to ensure safe and comfortable use of the mask.