1. National Transportation Safety Board Pipeline Accident Report Overpressurization of Natural Gas Distribution System Explosions and Fires in Merrimack Valley Massachusetts September 13 2018;2019 73 https://www.ntsb.gov/investigations/AccidentReports/Pages/PAR1902.aspx
2. Population of Lawrence Massachusetts;2020.https://suburbanstats.org/population/massachusetts/how‐many‐people‐live‐in‐lawrence Accessed January 21 2020.
3. North Andover Massachusetts Demographics Data https://www.towncharts.com/Massachusetts/Demographics/North‐Andover‐town‐MA‐Demographics‐data.html Accessed 4 February 2020.
4. Columbia Gas reaches $143 million settlement for Merrimack Valley explosions https://www.boston.com/news/local-news/2019/07/29/columbia-gas-settlement-merrimack-valley-explosions Accessed 4 February 2020.
5. OSHA 1910.119 ‐ Process safety management of highly hazardous chemicals https://www.osha.gov/laws‐regs/regulations/standardnumber/1910/1910.119 Accessed 13 February 2020.