hatch, is still the preferred option, as it allows crew members to avoid direct exposure to cold water and high pressure at depth. If a rescue vehicle is not available or cannot connect to a sunken submarine, the crew can escape using the SEIE. Another benefit of vehicle rescue as compared to escape with the SEIE is that there would likely be additional critical on-site resources available, such as a recompression chamber, that could be urgently needed by the rescued crew members. Reduced risk of decompression sickness, oxygen toxicity, carbon dioxide toxicity and nitrogen narcosis is dependent on a relatively high rate of pressurization and ejection from the escape lock, as all of these hazards are time-dependent. Use of a dedicated air supply further reduces risk of carbon dioxide toxicity. See also References External links History of Submarine Escape Immersion Equipment “Decompression Illness Associated with Submarine Escape and Rescue” (PDF file) A variant of the SEIE for use where thermal protection is not required (commercial link) "Initial review of the U.S. Navy's pressurized submarine escape training outcomes." Submarine rescue equipment Underwater diving safety equipment Military equipment introduced in the 1950s