Which figure of speech is used in this text?
I am just going outside and may be some time.
—Captain Lawrence Oates, Antarctic explorer, before going out into subzero temperatures to face certain death

 - understatement
 - chiasmus
The text uses understatement, which involves deliberately representing something as less serious or important than it really is.
May be some time is an understatement, since the frostbitten and weakened Oates knew that he was heading to his death.