1. http://www.csb.gov/assets/document/CSB_Study_TTU_.pdf, accessed 9/12/2012.
2. Recommendation 2010-5-I-TX-R4, found on page 19 in Reference #1.
3. http://www.csb.gov/investigations/detail.aspx?SID=96&Type=1&pg=1&F_All=y, see transcript of the public hearing on this page, accessed 12/10/2012.
4. Media articles describing the accidents with deaths, http://www.tmcnet.com/usubmit/2011/09/03/5750866.htm and http://archives.exploreharford.com/news/8733/contractor-dies-explosion-aberdeen-proving-ground/, accessed 09/13/2012.
5. Health and Safety Executive (HSE), Developing process safety indicators, HSE Books, London, 2006, p 1.