2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
70
METABOLIC PRODUCTION OF CO2 FOR HYPERBARIC
ESCAPE SYSTEMS IN SIMULATED SEA STATES
Phil Newton, Tara Reilly, Michael Tipton
Department of Sport & Exercise Science, Institute of Biomedical & Biomolecular
Sciences, Portsmouth University, UK
Contact person:phil.newton@port.ac.uk
INTRODUCTION
Hyperbaric Escape Systems (HES) are used when saturation diving bells have to be
evacuated and the divers transported to safety. HES vary in size but typically hold up
to 12 divers and have to be able to support life for up to 72 hours. Metabolically
produced carbon dioxide (CO2) has to be removed from the atmosphere within HES.
The current provision for scrubbing CO2 assumes a metabolic rate of 200W giving
487mL.min -1 per diver, assuming a respiratory exchange ratio (RER, carbon dioxide
production/oxygen consumption [VCO2/VO2]) of 0.82 1 . This volume assumes that
divers can remain secure and at rest in the seat of a HES, and that their metabolic rate
does not increase more than two-fold from that at seated rest despite differing wave
conditions. The aim of the present investigation was to obtain data on the CO2
production of subjects in a HES seat and 4-point harness in different wave states, with
a view to recommending a reasonable and safe requirement for scrubbing CO2 within
a HES. It was hypothesised that there would be no significant difference in the level
of metabolic carbon dioxide production in rough compared to calm wave conditions if
the subjects were able to remain at rest and engage in minimum levels of physical
activity
METHODS
Twenty healthy male volunteer subjects with a mean (SD) age of 36 (10) were
recruited from the RNLI (N=16) and University (N=4). The mean (SD) physical
characteristics of the subjects were: Mass (kg) 91.4 (31.6) with a range of 69-115kg.
Stature (m) 1.79 (0.06), range 1.66-1.90m. Percent body fat (2) was 23.1 (6.1), range
10.5-33%.
A HES seat with harness was secured to the bow of an Atlantic 75 rigid inflatable
lifeboat. Subjects sat in the HES seat, the 4-point harness was secured and the subjects
were instructed to rest. Although the subjects were not totally enclosed, they were
unable to see oncoming waves. The lifeboat was tethered at the bow and stern in the
sea survival wave tank. After 5 minutes of data collection in calm water (C), the
wave-maker was started and set to a “confused” wave motion profile. This profile
built over 30-60 seconds to produce 1.5-2m waves (Figure 1 and 2). The wave profile
was continued for 20 minutes. The initial orientation of the boat to the waves was
random and either: 1) longitudinally (L) to the waves for 10 minutes or 2) orientated
perpendicular (P) to the waves for 10 minutes.
A sample of the tests was filmed in the sagittal plane; these were analysed using SIMI
(reality motion systems software, Germany) two-dimensional motion analysis
a Assuming 1L oxygen consumption per minute = 20.2kJ per minute = 336.7W. Thus: (200W/336.7) x
0.82 = 0.487L carbon dioxide production per minute. For 12 divers over 24h: 0.487 x 12 x 60 x 24 =
8,415L. Diver respiratory exchange ratio (RER = VCO2/VO2) taken as 0.82 (typical for mixed diet).