@article{ref1,
title="Importance of Falling Ground, Rock, and Coal As an Accident Cause",
journal="Transactions of the American Institute of Mining and Metallurgical Engineers",
year="1943",
author="Boardman, JL",
volume="153",
number="",
pages="258-265",
abstract="[Abstract unavailable]  <p>Language: en</p>",
language="en",
issn="0096-4778",
doi="",
url="http://dx.doi.org/"
}