Flower Branch apartment complex in Silver Spring, Maryland, site of a deadly 2016 gas explosion. Photo: Jabin Botsford/Washington Post
October 7, 2020
The Pipeline and Hazardous Materials Safety Administration (PHMSA) has issued two Advisory Bulletins directed to natural gas distribution pipeline owners and operators. PHMSA released the advisories in response to the National Transportation Safety Board (NTSB) recommendations arising out of two high-profile distribution pipeline incidents in Silver Spring, Maryland and Merrimack Valley, Massachusetts. The first advisory focuses on indoor meters and regulators to remind operators of the relevant regulatory requirements and risks. The second advisory covers low-pressure distribution systems, emphasizing the possibility of failures due to overpressurization.
While advisory guidance does not create legal requirements, it does signal potential areas of renewed enforcement focus. Both advisories stress the importance of distribution integrity management programs (DIMP), including in particular effective leak detection, threat identification, risk reduction, and periodic evaluation. More specifics regarding each advisory are provided below.
By way of background, following a 2016 incident in Silver Spring, Maryland that caused an explosion and partial collapse of an apartment building, the NTSB investigation identified the probable cause as the failure of an indoor mercury service regulator with an unconnected vent line. The fact that the mercury service regulator was located in a space where leak detection by odor was not readily available contributed to the incident.
In response to the incident and the NTSB’s findings and recommendations, PHMSA’s advisory reminds distribution operators of the consequences of failures of inside meters and regulators and of the regulations applicable to these devices. Among others, these include requirements regarding installation in readily accessible locations and the additional requirement for indoor devices to be located as near to the point of service line entrance “as practical.” See 49 C.F.R. § 192.353; see also 49 C.F.R. §§ 192.355 (ventilation and venting); 192.357(d) (regulators must be vented to the atmosphere).
The advisory also reminds owners and operators of the requirement to conduct leakage and atmospheric corrosion surveys of their systems, which should also encompass indoor meters and service regulators (49 C.F.R. §§ 192.481 (corrosion); 192.723 (leak surveys)). PHMSA notes that if access to indoor regulators is an issue, operators should work with their customers to provide access for needed checks and surveys. In addition, operators should continue assessing risks to their systems and addressing those risks in accordance with their distribution integrity management programs (DIMP), which includes knowing the location of all meters and regulators, evaluating the risk of failure or damage to these devices, and addressing the risks. Specifically, PHMSA recommends that distribution operators review the points-of-failure identified in the NTSB accident investigation report, assess their systems in light of these failures, and adjust their DIMP if needed.
PHMSA issued its second advisory in response to the NTSB recommendations arising out of the September 13, 2018, natural gas pipeline incident in Merrimack Valley, Massachusetts. The NTSB identified the probable cause of the accident as weak engineering management and specifically the operator’s failure to relocate regulator sensing lines when conducting main replacement on the system. As a contributing cause, NTSB identified a lack of adequate overpressure protection on the low-pressure system.
In its advisory, PHMSA reminds operators of low-pressure systems to thoroughly review their current DIMP for the threat of overpressurization and to make necessary changes. In particular, PHMSA recommends that operators develop written procedures for all activities involving new construction or pipe replacement projects for their low-distribution systems to account for the additional precautions needed to protect them from overpressurization. The advisory offers a list of topics to be covered in such procedures. Further, PHMSA recommends that while identifying threats and ranking risks, operators consider the single point of failure that could lead to an overpressurization as a high-risk threat, given the Merrimack Valley incident. If operators do not consider the threat of overpressurization as an existing threat in their DIMP programs, PHMSA suggests they provide a written justification. PHMSA also urges operators to use a failure modes and effectiveness analysis (FMEA) model or an equivalent method when performing risk analysis. Lastly, PHMSA reminds operators to implement measures designed to reduce the risk of overpressure events and provides several means for doing that.