Opening 2 : A gap or void 30 inches (76 centimeters) or more high and 18 inches (46 centimeters) or more wide, in a wall or partition, through which employees can fall to a lower level
Environmental Health and Safety, Glossary, University of Chicago, Illinois, USA 2010. http://safety.uchicago.edu/tools/glossary.shtml, (Ergo - Amer) {753}