Carbon Monoxide Accumulation in Closed, Manned Environments

Abstract

ABSTRACT Carbon monoxide (CO) is a colourless, odourless and tasteless gas slightly less dense than air. Its main health significance as a contaminant is that it combines with hemoglobin (Hb) and other oxygen transporting proteins in the body and, thus, impairs the oxygen-carrying capacities of these. CO is produced by incomplete combustion of carbon-containing fuels, but is also continuously produced by the body, mainly through breakdown of heme, one of the constituents of Hb in the red blood cells. Accumulation of CO has been monitored in two different isolation studies with different atmospheric pressures, 1) at 150 kPa(ISEMSI study), lasting 28 days, and 2) at 4600 kPa (IGLOO ’88), lasting 33 days. Two different groups of six male subjects were isolated. In the high pressure investigation (HPI), the Threshold Limit Value (TLV) as given by the Norwegian Petroleum Directorate (NPD), i.e. 2 Pa (20 ppm) bar, was exceeded on isolation day nine, upon which a CO-catalyst was introduced. In the low pressure investigation (LPI) the TLV value was not reached during the study, requiring no such intervention. CO accumulated faster in the first 10-12 days, than in the later part of the LPI. CO accumulation in the LPI averaged 82 mPa/day, corresponding well with the endogenous production rate published by others. CO accumulation rate was slightly faster, i.e. 103 mPa/day, in the HPI than in the LPI, possibly due to a decrease in Hb of approximately 9% during the first 10 days. In both isolation studies, venous blood samples were collected for caboxy- hemoglobin analysis. It is concluded that partial pressure of CO may reach values that calls for intervention during saturation dives as well as in other situations where people are enclosed for longer periods of time. Operational procedures to prevent this from happening should therefore be introduced.