Although I agree with the posts that you should not fill you PCP with oxygen, I must correct a few things. Oxygen is not flammable, combustible or explosive. It is an oxidizer which means it makes things burn much quicker. It also reacts with hydrocarbons such as oils and grease. Therefore, if oxygen is in your PCP, it will surely react violently with any lubricants that it comes in contact with. Technically not an explosion, but in essence the end result is the same.
Rich