Design and Validation of a Breathing Detection System for Scuba Divers.

Drowning is the major cause of death in self-contained underwater breathing apparatus (SCUBA) diving. This study proposes an embedded system with a live and light-weight algorithm which detects the breathing of divers through the analysis of the intermediate pressure (IP) signal of the SCUBA regulator. A system composed mainly of two pressure sensors and a low-power microcontroller was designed and programmed to record the pressure sensors signals and provide alarms in absence of breathing. An algorithm was developed to analyze the signals and identify inhalation events of the diver. A waterproof case was built to accommodate the system and was tested up to a depth of 25 m in a pressure chamber. To validate the system in the real environment, a series of dives with two different types of workload requiring different ranges of breathing frequencies were planned. Eight professional SCUBA divers volunteered to dive with the system to collect their IP data in order to participate to validation trials. The subjects underwent two dives, each of 52 min on average and a maximum depth of 7 m. The algorithm was optimized for the collected dataset and proved a sensitivity of inhalation detection of 97.5% and a total number of 275 false positives (FP) over a total recording time of 13.9 h. The detection algorithm presents a maximum delay of 5.2 s and requires only 800 bytes of random-access memory (RAM). The results were compared against the analysis of video records of the dives by two blinded observers and proved a sensitivity of 97.6% on the data set. The design includes a buzzer to provide audible alarms to accompanying dive buddies which will be triggered in case of degraded health conditions such as near drowning (absence of breathing), hyperventilation (breathing frequency too high) and skip-breathing (breathing frequency too low) measured by the improper breathing frequency. The system also measures the IP at rest before the dive and indicates with flashing light-emitting diodes and audible alarm the regulator malfunctions due to high or low IP that may cause fatal accidents during the dive by preventing natural breathing. It is also planned to relay the alarm signal to underwater and surface rescue authorities by means of acoustic communication.

Diving at altitude: from definition to practice.

Diving above sea level has different motivations for recreational, military, commercial and scientific activities. Despite the apparently wide practice of inland diving, there are three major discrepancies about diving at altitude: threshold elevation that requires changes in sea level procedures; upper altitude limit of the applicability of these modifications; and independent validation of altitude adaptation methods of decompression algorithms. The first problem is solved by converting the normal fluctuation in barometric pressure to an altitude equivalent. Based on the barometric variations recorded from a meteorological center, it is possible to suggest 600 meters as a threshold for classifying a dive as an "altitude" dive. The second problem is solved by proposing the threshold altitude of aviation (2,400 meters) to classify "high" altitude dives. The DAN (Divers Alert Network) Europe diving database (DB) is analyzed to solve the third problem. The database consists of 65,050 dives collected from different dive computers. A total of 1,467 dives were found to be classified as altitude dives. However, by checking the elevation according to the logged geographical coordinates, 1,284 dives were disqualified because the altitude setting had been used as a conservative setting by the dive computer despite the fact that the dive was made at sea level. Furthermore, according to the description put forward in this manuscript, 72 dives were disqualified because the surface level elevation is lower than 600 meters. The number of field data (111 dives) is still very low to use for the validation of any particular method of altitude adaptation concerning decompression algorithms.

Commercial diver selection using multiple-criteria decision-making methods.

INTRODUCTION: Personnel selection for different commercial diving jobs is time-consuming and subjective, This paper proposes a combination of two multiple-criteria decision-making (MCDM) methods to provide an objective tool for evaluation according to two main selection criteria: work experience and physical fitness. METHOD: Subcriteria were computed using the analytic hierarchy process (AHP). By consulting two field professionals, subcriteria for work experience were determined as: working hours on the project type, hand tools, hydraulic tools, pneumatic tools, LP air jet and water lift/dredge, wet bell diving and paramedic training level. Determined by three medical experts, the subcriteria for physical fitness were: age, VO2Max, critical flicker fusion frequency (CFFF), psychomotor performance, and visual and hearing acuities. The pair-wise comparison matrices used to calculate subcriteria weights are filled by the same experts. Eight divers were included in the analysis. The AHP yielded scores of work experience for seven different project types and a physical fitness score for each diver. These scores were used in data envelopment analysis (DEA), to obtain an aggregate ranking of the divers. RESULT: The methodology was able to differentiate between qualified and unqualified divers. Divers were scored between 0 and 1 for each project type. The overall ranking of divers according to the average of the seven project types' scores was: 1. Diver 7 (1.0000); 2. Diver 5 (0.9486); 3, Diver 8 (0.9453); 4. Diver 2 (0.9421); 5. Diver 3 (0.8441); 6. Diver 4 (0.7804); 7. Diver 6 (0.6554); 8. Diver 1 (0.3931). DISCUSSION: The proposed methodology allows decision-makers to perform evaluations objectively and systematically, reducing personal conflicts and confusions resulting from subjective immethodical judgments. This methodology is to be applied in real projects to validate the selection criteria and confirm the results.