Carbon dioxide re-breathing in respiratory protective devices; Influence of speech and work rate in full face masks

It is estimated that five million workers throughout the United States of America rely on Respiratory Protective Devices (RPDs) to protect their health. However, there are a number of factors that limit the wear time of RPDs in the workplace. This includes high breathing resistance, interference with vision, heat stress, difficulty communicating and re-breathing of carbon dioxide (CO2). Of these factors there has been little research into the adverse affects to CO2 re-breathing in RPDs. CO2 is known to stimulate respiration, increase heart rate, dilate blood vessels and in higher concentrations produces symptoms of discomfort, anxiety, headache, fatigue, dizziness and shortness of breath. Previous investigations on CO2 re-breathing are limited by small sample size and have not evaluated the relationship between CO2 inhalation and phonic respiration (breathing during speech) in RPDs. This research was conducted in two parts, a pilot study at the University of Wollongong, New South Wales and a field study at a worksite in Mount Isa, Queensland. Participants took part in a graded exercise test on a bicycle ergonometer that increased in resistance every five minutes. During the third minute of each stage participants read aloud a prepared text. Measures of expired CO2 (PECO2), inspired CO2 (PICO2) and respiration were monitored. The results showed phonic respiration and low work rates contributed to significantly higher levels of CO2 re-breathing. Aiming to reduce CO2 re-breathing may result in improved wear time of RPDs. It is recommended that these findings be incorporated in technical specifications regarding human factors for RPDs.