diff options
Diffstat (limited to 'core/divelist.c')
| -rw-r--r-- | core/divelist.c | 43 |
1 files changed, 34 insertions, 9 deletions
diff --git a/core/divelist.c b/core/divelist.c index b10c4604b..1dc4e3d8a 100644 --- a/core/divelist.c +++ b/core/divelist.c @@ -159,27 +159,52 @@ static int active_o2(const struct dive *dive, const struct divecomputer *dc, dur return get_o2(gas); } -/* calculate OTU for a dive - this only takes the first divecomputer into account */ +/* Calculate OTU for a dive - this only takes the first divecomputer into account. + Implement the protocol in Erik Baker's document "Oxygen Toxicity Calculations". This code + implements a third-order continuous approximation of Baker's Eq. 2 and enables OTU + calculation for rebreathers. Baker obtained his information from: + Comroe Jr. JH et al. (1945) Oxygen toxicity. J. Am. Med. Assoc. 128,710-717 + Clark JM & CJ Lambertsen (1970) Pulmonary oxygen tolerance in man and derivation of pulmonary + oxygen tolerance curves. Inst. env. Med. Report 1-70, University of Pennsylvania, Philadelphia, USA. */ static int calculate_otu(const struct dive *dive) { int i; double otu = 0.0; const struct divecomputer *dc = &dive->dc; - for (i = 1; i < dc->samples; i++) { int t; - int po2; + int po2i, po2f; + double pm; struct sample *sample = dc->sample + i; struct sample *psample = sample - 1; t = sample->time.seconds - psample->time.seconds; - if (sample->setpoint.mbar) { - po2 = sample->setpoint.mbar; + if (sample->o2sensor[0].mbar) { // if dive computer has o2 sensor(s) (CCR & PSCR) .. + po2i = psample->o2sensor[0].mbar; + po2f = sample->o2sensor[0].mbar; // ... use data from the first o2 sensor } else { - int o2 = active_o2(dive, dc, psample->time); - po2 = lrint(o2 * depth_to_atm(sample->depth.mm, dive)); + if (dc->divemode == CCR) { + po2i = psample->setpoint.mbar; // if CCR has no o2 sensors then use setpoint + po2f = sample->setpoint.mbar; + } else { // For OC and rebreather without o2 sensor/setpoint + int o2 = active_o2(dive, dc, psample->time); // ... calculate po2 from depth and FiO2. + po2i = lrint(o2 * depth_to_atm(psample->depth.mm, dive)); // (initial) po2 at start of segment + po2f = lrint(o2 * depth_to_atm(sample->depth.mm, dive)); // (final) po2 at end of segment + } + } + if ((po2i > 500) || (po2f > 500)) { // If PO2 in segment is above 500 mbar then calculate otu + if (po2i <= 500) { // For descent segment with po2i <= 500 mbar .. + t = t * (po2f - 500) / (po2f - po2i); // .. only consider part with PO2 > 500 mbar + po2i = 501; // Mostly important for the dive planner with long segments + } else { + if (po2f <= 500){ + t = t * (po2i - 500) / (po2i - po2f); // For ascent segment with po2f <= 500 mbar .. + po2f = 501; // .. only consider part with PO2 > 500 mbar + } + } + pm = (po2f + po2i)/1000.0 - 1.0; + // This is a 3rd order continuous approximation of Baker's eq. 2, therefore Baker's eq. 1 is not used: + otu += t / 60.0 * pow(pm, 5.0/6.0) * (1.0 - 5.0 * (po2f - po2i) * (po2f - po2i) / 216000000.0 / (pm * pm)); } - if (po2 >= 500) - otu += pow((po2 - 500) / 1000.0, 0.83) * t / 30.0; } return lrint(otu); } |