On February 27, 2014 a fire occurred in the forward battery compartment of Austrialia's Collins submarine HMAS Waller. Fires in submarine battery compartments can be caused by the release of hydrogen gas from the batteries. [http://www.pmbatteries.com.au/batteries/history-of-diesel-electric-submarines
The fire immediately triggered the Waller's emergency system, filling the foreward battery compartment with inert Freon gas to smother the flame. Release of Freon gas can be deadly if all of a submarine's crew, technicians and observers do no have access to oxygen breathing masts - or do not know when or how to use such masks in an emergency. In 2008 aboard the then Russian submarine Nerpa (now Indian INS Chakra) 20 people where killed by an accidental release of Freon - see http://en.wikipedia.org/wiki/2008_Russian_submarine_K-152_Nerpa_accident#Sequence_of_events and also http://gentleseas.blogspot.com.au/2012/05/nerpa-accident-sets-back-indian.html. In Nerpa's case many of the 20 were observer-technicians without knowledge of or access to oxygen breathing masks.
In HMAS Waller's February 27, 2014 case presumably the crew had knowledge of and access to masks. They survived the fire and the Freon release. see http://news.defence.gov.au/2014/02/27/fire-onboard-royal-australian-navy-submarine/
On the Waller emergency Australia's news.com.au reported on February 28, 2014:
"Fire emergency aboard HMAS Waller as Indian submarine blaze kills two
A FIRE sparked an emergency aboard submarine HMAS Waller off the West Australian coast yesterday, the same day as a fire in an Indian vessel killed two and injured seven.