Ullage 06 : The air space left in a container when it is nominally full so that any expansion of the liquid will not cause overflow or excessive hydraulic pressure
Ministry of Business, Innovation and Employment, Glossary of terms and acronyms, Wellington, New Zealand 2010. http://wwwsosh.govt.nz/resources/glossary-u.shtml, (Occupn Hlth and Sfty - Brit) {530}