Measurement of atmospheric oxides of nitrogen and a preliminary investigation of their source

Abstract

Maintenance of a breathable atmosphere is a core tenet of dived submarine operations, and the responsibility for this falls to the medical department. Nitrogen oxides (NOx) are atmospheric contaminants from a currently unconfirmed source. If not controlled, these contaminants can act as respiratory irritants and asphyxiants which may endanger health and threaten sustained dived operations. Using the issued Dräger Short Term Detection Tubes (STDTs) to sample strategic locations, the relationship between atmospheric contaminants and NOx was investigated in an attempt to determine the source of NOx formation. Interventions were implemented to reduce NOx by reducing leakage of monoethanolamine (MEA) from carbon dioxide (CO2) scrubbing equipment, a known potential source of NOx if oxidised (combusted). Dräger STDTs for NH3 demonstrate cross-reactivity with MEA, these levels being referred to as NH3/MEA. A relationship was demonstrated between elevated readings for atmospheric NH3/MEA and elevated readings for NOx, with a variable lag period. Findings suggest that NOx production may be reduced by control of atmospheric NH3/MEA. Of the control measures examined, replacement of resin filter bags was noted to reduce atmospheric NH3/MEA, while replenishment of CO2 scrubber MEA was noted to increase it, with a resultant increase in NOx production. Elevated NH3 atmospheric readings may in fact be due to MEA from CO2 scrubbers. This, when catalytically oxidised by CO/H2 burners, produces NOx. Management of MEA egress from CO2 scrubbers (carryover) represents a potential target for NOx control interventions. Specific MEA detection equipment is required to demonstrate whether MEA or NH3 is the progenitor species for NOx. Furthermore, controlled trials are required to prove a definitive relationship between MEA and NOx and to evaluate the best control measures.