In 2008 the US military transitioned to a central, electronic dive logging system called the Dive Jump Reporting System, DJRS. Meant to increase visibility on diving trends and maintain an accessible system to view dive currency, the system has been a great asset to the dive community and its leadership.
In the summer of 2015, I requested the largest data draw in DJRS history: every electronic dive log and dive related mishap since DJRS implementation. Following a Freedom of Information Act request, the Naval Safety Center, owner and maintainer of the system, provided 768,851 dive log entries and 39 mishap reports (since 2008). In addition to the DJRS data, Atmospheric Dive Suit (ADS) dive logs were collected from the Portsmouth Naval Shipyard to further strengthen the dataset. Saturation Dive logs, however, were not obtained. With six years’ worth of military dive history, we can quantitatively learn a lot about our community.
Figure 1 is a traditional histogram showing all military dives since 2008. All services, types of diving rigs, and tasks are represented. Some technical notes: (1) dives are broken into incremented 10 foot “bins,” starting from the left limit; (2) The blue columns represent the total number of dives on a logarithmic scale; and (3) The orange line represents the cumulative percentage (Empirical Cumulative Distribution Function, ECDF) of dives achieved to a given depth.
One of the first numbers from the dataset that may come as a surprise is the average dive depth: 27.8 feet. This number is driven by high instances of 10-29 foot dives (20 foot dives representing the data set median). Additionally, nearly 60% of all dives have “unlimited” dive time and 90% of all completed dives have been less than 60 feet. Consider yourself in an exclusive club the next time you dive greater than 60 feet.
Figures 2 illustrates “how” the military dives. DJRS broke down each documented dive by job type, tagging each entry with a general “Dive Description.” Each bin is normalized to the total number of dives within the given depth bin. Figure 2 illustrates a group normalized percentage for each given dive type. For example, between 260 and 269 feet, 50% of time was spent on Experimental Testing, and the other 50% was spent on Search. Most depth bins are dominated by training. Training (Diver), Supervisor Training, and Student Training represent 57% of all diving depths less than 190 feet. Interesting things to see: (1) The community spends a considerable amount of time on Experimentation, specifically at deeper depths; (2) Pressure Testing for dive candidates and Recompression treatments make an appreciable appearance in the 60 foot depth bin; and (3) Requalification dives are generally very shallow (10-19 feet).
When all training and non-operational diving types are removed (clicking on legend descriptions), Figure 2 can show a clear visual of all diving work. The shallower depths are dominated by harbor work: U/W Construction, Ship’s Husbandry, Security Swim, Routine Working Dives, Inspection/Survey, and Force Protection. As depth increases, the dive profile is dominated by Salvage, Search, and EOD work.
Figure 3 breaks out the data by Service affiliation. As expected, the Navy dominates the number of dives completed at each depth. Army Divers make up the next highest percentage of dives at almost all depths. This chart represents all types of diving.
In Figures 4 and 5, the diving data is segmented by apparatus type. This is the first time ADS dive history is included, although at a very small fraction. The pie chart in Figure 5 represents the average apparatus use per year. The group normalized chart in Figure 6 shows how apparatus use relates to depth. Note the depth axis stops at 310 feet, above which, the ADS is the only rig used, absent of saturation diving (data not included). “Oxygen Rebreathers” represents MK-25 variants, “Mixed Gas Rebreather” represents MK-16 (Air and Helium diluents) or similar variants, “Other” includes experimental or similar rigs, “Surface Supplied” represents MK-21 and KM-37 similar variants (mixed gas and air), and SCUBA and Chamber dives represent their namesake.
SCUBA dominates shallower depths and trails off until its upper authorized-use limit (190 feet). The 5 SCUBA dives seen at 200 feet were recorded by NEDU. Mixed Gas Rebreathers and Surface Supplied diving takes over when the depth becomes deeper. Few dives (536 total, less than 100 per year) were completed to depths greater than 200 feet, so the apparatus use percentages are more variable and sensitive.
Figure 6 buckets the dives by year. Given 2008 represented the start of DJRS and only partial data was received for 2015, the following chart represents the dive breakdown from 2009 through 2014. Although the number of dives increased steadily over the years, all previous analyses were annually consistent. On average, as a combined military diving community, more than 115,000 dives are logged per year. Over 45 dives occur every working hour (assuming 250 day work year and 10 hour work day). Rest easy knowing somewhere one of your fellow divers is breathing compressed gas.
When originally analyzing this dataset, I noticed inconsistencies with a small portion of dive logs. Specifically, SCUBA dives were frequently displayed above 200 feet. Upon further inspection, I identified nearly 13,000 misreported dive records (~1.5% of all logs). Those misreported dive records either reported a Max Depth greater than Schedule Depth or did not record a Schedule Depth. In some instances, it was easy to identify a mistype error (Schedule Depth of 30 feet, Max Depth of 300 feet) and others where the Schedule Depth was zero, indicated an untrustworthy dive log. I excluded all questionable dive log data from this analysis.
The following Navy and Marine Corps diving mishap data is presented for dive community situational awareness. Most years contain dive mishaps in the single digits and the annual mishap rate (mishaps per number of dives) represents less than a hundredth of a percent. While the community has experienced a limited number of diving related mishaps, this absence of data makes forming solid statistical analysis less impactful, but speaks highly of training, supervision, equipment, and technical prowess within the community.
Mishaps collected from the Naval Safety Center represent an “injury, recompression therapy, or death resulting from an incident occurring while breathing compressed gases … before, during, or after entering or leaving the water” (OPNAVINST 5102.1). 39 mishap reports since 2008 were provided by the Naval Safety Center. Two known mishaps from February 2013 (not provided by the Safety Center) were added to the dataset to ensure its completeness. One additional report was corrected based on an erroneously reported max depth. Overall, 41 mishaps were analyzed.
Figure 7 shows the mishap histogram (2008-mid 2015) with associated diving mishap type illustrated below. A strong statistical correlation (+0.85) was observed between number of dives and number of mishaps. Meaning, there exists a positive and predictive linear relationship between the number of dives and the number of mishaps. Related, there is a moderate negative correlation (-0.65) between mishaps and depth, meaning more mishaps at shallower depths.
As the bottom chart of Figure & shows, diving related illnesses are real casualties experienced in the fleet. For example, Pulmonary Over Inflation Syndrome (POIS), specifically Arterial Gas Embolism (AGE), is found experientially throughout our diving range – divers are always at risk, no matter the depth.
Figure 8 represents the Navy and Marine Corps diving histogram (logarithmic scale) overlaid with the Mishap Rate during the last six years. Note the Mishap Rate can be identified by the right y-axis and only reaches a maximum of 0.53% in the 150-159 foot depth bin.
Although the Mishap Rate value is very small, there does exist a statistically significant change in Mishap Rates from the 0-99 to 100-170 foot depth. This statistical significance prompted further inspection. The majority of the mishaps in the 100-170 foot depth band (9 of 14) are air diluent MK-16 dives, including one fatality. 3 of 14 dives are HeO2 diluent MK-16 dives. The last mishaps in this depth band are two fatal SCUBA dives in February of 2013. Overall, nearly 80% of mishaps in this depth band occurred while breathing air.
Further analysis of the association between apparatus and mishaps is shown in Figure 9. A cumulative 22 Mixed Gas Rebreather mishaps across the depth band, 14 O2 Rebreather mishaps between 10 and 30 feet, 4 SCUBA mishaps, and 1 Surface Supplied mishap were reported. The supplemental notes on the chart indicate the maximum individual Apparatus Mishap Rate. Generally very low, the Apparatus Mishap Rate helps put in perspective the “spikes” seen in Figure 10. In the case of the 50% SCUBA Mishap Rate in the 150-159 foot depth bin, this statistic is an outlier but highlights the rarity in which SCUBA is used for deep diving. Only 60 logged SCUBA dives since 2008 were completed at 150 feet or greater, with 2 reported mishaps (overall 3.3% Mishap Rate for “deep” SCUBA dives).
I hope you all enjoyed the quantitative look at the military diving community since the launch of DJRS. Thanks for viewing and dive safe!
A special thank you to the Naval Safety Center for honoring this data request and allowing military divers to better understand the state of the community.
posted by J. Colgary 15 December 2015
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