Interesting that they only had a single regulator, if overpressure is that dangerous, I would expect them to have multiple regulators in sequence or a blowout valve to dump excess pressure.
After the accident, the Massachusetts legislature passed a law to require a licensed professional engineers stamp on all gas infrastructure designs of this type
But the recommendations to the gas company included:
> Review and ensure that all records and documentation of your natural gas systems are traceable, reliable, and complete. (P-18-7) (Urgent)
> Apply management of change process to all changes to adequately identify system threats that could result in a common mode failure. (P-18-8) (Urgent)
> Develop and implement control procedures during modifications to gas mains to
mitigate the risks identified during management of change operations. Gas main
pressures should be continually monitored during these modifications and assets
should be placed at critical locations to immediately shut down the system if
abnormal operations are detected. (P-18-9) (Urgent)
Edit to add:
This page has currently working links to the specific recommendations:
Well, my reading is that the corrective action was less "add redundant safeties" and more "have sufficient process controls in place to ensure you don't break the feedback loop during pipeline work".
One potential problem with a pressure relief valve as a safety is that it could turn into a flare/blowtorch if there is an ignition source nearby, which constrains where it can be located (and requires ongoing maintenance to ensure vegetation/etc., doesn't build up where it could get torched).