August 23, 2019 – Naval Medical Research Center (NMRC) scientists presented their research, “Determining DISSUB survival rates rescued subjects using Submarine Rescue Diving and Recompression System (SRDRS) standard operating procedures,” during the Military Health System Research Symposium (MHSRS) in Kissimmee, Florida Aug. 22.
“The Undersea Rescue Command in San Diego made the initial request to evaluate survivability,” said Lt W. Rainey Johnson, undersea medical officer. “Supporting disabled submarine (DISSUB) rescue is a pillar of the Undersea Medicine Department (UMD) research mission.”
Survivability was evaluated following current Navy standard operating procedures for disabled submarine rescue at the operable limits of the rescue equipment. The study evaluated the Submarine Rescue System (SRS), a section of the Submarine Rescue Diving and Recompression System (SRDRS), decompression plan.
According to Johnson, DISSUB rescue is a complicated and resource-intensive process.
“Current rescue systems require transport to the DISSUB site, modification of a vessel of opportunity, and round-the-clock operation of mobile hyperbaric chambers, which can take several days,” he said.
According to Dr. Aaron Hall, Ph.D., supervisory research physiologist, Underwater Medicine Department, the DISSUB rescue plan was designed based on projected survival of the crew and engineered capabilities of the rescue system.
“A surrogate model was used to expose subjects to the most extreme environmental conditions described in the decompression plan, specifically an atmospheric pressure inside the submarine five times the pressure at sea level,” he said. “Because of the known risk of pulmonary oxygen toxicity, which could result in severe injury and/or death, it is unethical to use human subjects to test the concept of operations for the most extreme conditions thought to be survivable.”
Under the extreme high pressure conditions inside the submarine the subjects did not survive beyond 55 hours, less than the 72 hours currently in place to rescue survivors in a DISSUB scenario.
Based on their initial study, Johnson, Hall, and colleagues agree survivability of the current DISSUB rescue plan is uncertain when atmospheric pressure inside a submarine rises to five times greater than the atmospheric pressure at sea level. They caution the study does not address survivability during less extreme DISSUB scenarios, and emphasize additional research must be done.
“Factors limiting DISSUB survivability are likely related to internal pressure and atmospheric composition, but further research is needed,” Johnson said. “The next steps are to confirm the findings in a second model, identify physiologic factors limiting survivability, and develop countermeasures that will improve outcomes during DISSUB escape and rescue.”