March 29, 2007: On March 21st, the British attack submarine (SSN) HMS Tireless lost two men when a SCOG (Self-Contained Oxygen Generator) exploded during a training exercise. The SCOG apparently had some of its vents clogged or blocked. That's a dangerous situation. A SCOG works by burning (at about 1,100 degrees Fahrenheit) sodium chlorate and iron powder, which releases oxygen. For every pound of material burned, there's enough oxygen produced to keep a man alive for three hours. These cylindrical devices are commonly called "oxygen candles." They are only used in emergencies, or in combat situations where maximum silence is required (to avoid enemy detection.) The normal oxygen producing and distribution system contains machinery that makes some noise. The SCOGs are much quieter. The most recent "oxygen candles" are actually square, but are unwrapped, visually inspected and inserted into the SCOG just like the older cylindrical ones.

HMS Tireless was participating in an exercise in the Arctic Ocean, off the coast of Alaska, with American forces. After the explosion, a commercial helicopter met the surfaced sub and transported a third sailor, who was injured by the exploding SCOG, to a nearby airstrip. There, a U.S. Air National Guard C-130 took the British sailor to a major hospital in Anchorage, Alaska. From the time of the explosion, to the burned sailor arriving at the regional hospital, took about six hours.

There was no serious damage done to the submarine. The exact cause of the explosion won't be known for a while, but it was probably a defective SCOG (clogged vents or other poor construction).