Hi,
The LOB_TABLESPACE stores binary files, eg. attachments, uploaded files, etc for the incidents. So the more and bigger files you have, the faster it will increase. It's worth to think in advance about what files to keep with incident data, as it's not easy to shrink the LOB_TABLESPACE later. Oracle will not shrink the DBF files even if you delete the incidents, it will keep their sizes and reuse the files later.
You can manage / add tablespace files and settings from Oracle Enterprise Manager, see a howto here:
http://www.dbtalks.com/UploadFile/anjudidi/771/
Be careful with it!