@article{ref1,
title="Permissible levels for occupational exposure; basic concepts",
journal="International archives of occupational and environmental health",
year="1979",
author="Zielhuis, R. L. and Notten, W. R.",
volume="42",
number="3-4",
pages="269-281",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0340-0131",
doi="",
url="http://dx.doi.org/"
}