Abstract: A critical parameter monitoring system for improving the safety of personnel working in a remotely located hazardous location possibly containing combustible materials include an oxygen and a temperature sensor carried by the personnel. The sensors are connected to a centrally located processor which displays the oxygen level and temperature present at the sensors and issues a warning when the measured parameters exceed preset levels. The monitoring system may be a part of a breathing apparatus which supplies air and voice communications from the centralized location to personnel working in a vessel purged with an inert gas. The measured oxygen level may also be used to conserve the quantity of inert gas used in the purging process while preserving the safety of the workers.