NTSB Safety Recommendation P-19-011

NTSB safety recommendation P-19-011.

TO THE WASHINGTON GAS LIGHT COMPANY: Establish a time frame with specific dates and milestones for the replacement of mercury service regulators throughout the Washington Gas network that recognizes the need to expedite this program and that prioritizes multifamily dwellings where mercury service regulators are located inside the property.

Priority: CLASS II

Overall Status: Closed - Acceptable Action

Issued Date: 2019-06-10

Overall Date Closed: 2025-09-26

Synopsis: On August 10, 2016, at 11:51 p.m., eastern daylight time, a 14-unit apartment building, located at 8701 Arliss Street, in the unincorporated community of Silver Spring, in Montgomery County, Maryland, partially collapsed due to a natural gas-fueled explosion and fire. The explosion and fire also heavily damaged an adjacent apartment building, 8703 Arliss Street, which shared a common wall with building 8701. As a result of this accident, 7 residents died, 65 residents were transported to the hospital, and 3 firefighters were treated and released from the hospital. The damage from the accident exceeded $1 million. The following are safety issues in this accident: • the location and inspection of service regulators within a structure • the inspection of the gas meter assembly • the notification of the natural gas odor to Washington Gas Light Company • the detection of natural gas through odorants and methane

Probable Cause: The National Transportation Safety Board determines that the probable cause of the explosion in building 8701 of the Flower Branch apartment complex was the failure of an indoor mercury service regulator with an unconnected vent line that allowed natural gas into the meter room where it accumulated and ignited from an unknown ignition source. Contributing to the accident was the location of the mercury service regulators where leak detection by odor was not readily available.

Keywords: Hazmat

Ntsbnumber: DCA16FP003

Report Number: PAR-19-01

Addressee Name: Washington Gas

Addressee Status: Closed - Acceptable Action

Addressee Date Closed: 2025-09-26

Addressee Organization Type: P-Private Industry

Communication Date: 2019-06-10

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge your organization to act on the safety recommendations in this letter because we believe your organization can help reduce the risk of future accidents. For more information about NTSB and our recommendation process, please see the attached one-page summary. On April 24, 2019, the NTSB adopted its report, Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016, NTSB/PAR-19/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, the NTSB identified the following safety issues: • The location and inspection of service regulators within a structure. • The inspection of the gas meter assembly. • The notification of the natural gas odor to Washington Gas Light Company. • The detection of natural gas through odorants and methane. Accordingly, the NTSB makes the following safety recommendations to the Washington Gas Light Company. Additional information regarding these recommendations can be found in the noted sections of the report. • Throughout the Washington Gas network, implement an audit program to verify the data on the service forms used to determine the location and condition of mercury service regulators to ensure the accuracy of this safety-critical data. (P 19 009) (See section 2.3.9.) • Revise your procedures and field forms to require technicians to verify the integrity of vent lines following the testing of indoor service regulators throughout the Washington Gas network. (P-19-010) (See section 2.3.5.) • Establish a time frame with specific dates and milestones for the replacement of mercury service regulators throughout the Washington Gas network that recognizes the need to expedite this program and that prioritizes multifamily dwellings where mercury service regulators are located inside the property. (P-19-011) (See section 2.3.10) • Install all new service regulators outside occupied structures. (P-19-012) (See section 2.3.10.) • Relocate existing interior service regulators outside occupied structures whenever the gas service line, meter, or regulator is replaced. In addition, multifamily structures should be prioritized over single-family dwellings. (P-19-013) (See section 2.3.10.) The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days, detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendations by number (for example, P-19-009). We encourage you to submit your response to correspondence@ntsb.gov. If your reply exceeds 20MB, including attachments, please e-mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response.

Addressee Organization Type: P-Private Industry

Communication Date: 2019-09-09

Communication Type: Official Correspondence

Communication Contents: -From Adrian Chapman, President and Chief Executive Officer, WGL (Washington Gas Light): In progress, currently working on a schedule with each of our three Public Service Commissions, which includes the prioritization of multi-family dwellings. For additional detail, please see the attached submissions to the District of Columbia, Maryland and Virginia public utility commissions. Consistent with Washington Gas's commitment to operating a safe and reliable system, we propose to undertake the above actions as enhancements to the safety of our system and consistent with our regulatory obligation as a safe and prudent operator. Nothing in this letter or in the proposed actions to be taken should be misunderstood as agreement with the NTSB's determination of probable cause in this matter.

Addressee Organization Type: P-Private Industry

Communication Date: 2020-05-29

Communication Type: Official Correspondence

Communication Contents: -From Donald “Blue” Jenkins, President, Washington Gas: Washington Gas is proceeding with the implementation of this recommendation in accordance with its proposals before each of its state regulatory commissions. A formal Request for Proposal (“RFP”) has been issued to obtain the necessary qualified resources for this program. The RFP has requested bidders address the following milestone timeframes for completion of the program: A) Completion of a multi-family mercury regulator survey within year 1, and replacement of multi-family mercury regulators within 3 years; and completion of non-multi-family mercury regulator survey within 3 years, and replacement of non-multi-family mercury regulators within 5 years. Washington Gas also requested bidders to address an alternative milestone timeframe: B) Completion of a multi-family mercury regulator survey within 3 years, and replacement of multi-family mercury regulators within 5 years; completion of non-multi-family mercury regulator survey within 5 years, and replacement of non-multi-family mercury regulators within 10 years. The alternate milestone timeframe provides for efficiencies in the replacement of mercury regulators through the Company’s existing accelerated pipe replacement programs. Those efficiencies have been shared with the Company’s state regulatory commissions. The Company’s intent is to meet the milestone timeframes under alternative A, for the shorter replacement period, but will abide by the respective commission orders and/or legislative enactments in this regard. A contract award pursuant to the procurement process is expected to be completed within the next 60-90 days.

Addressee Organization Type: P-Private Industry

Communication Date: 2025-04-15

Communication Type: Official Correspondence

Communication Contents: -From Donald “Blue” Jenkins, Executive Vice President, Utilities- AltaGas, President- Washington Gas: Thank you for your March 24, 2025, email inquiry regarding Safety Recommendation P-19-11 issued on June 10, 2019, by the National Transportation Safety Board (“NTSB”) as a result of the investigation of the August 10, 2016, explosion and fire at the Flower Branch apartment building in Silver Spring, Maryland, serviced by Washington Gas Light Company (“Washington Gas,” “WGL,” or “Company”). As noted in your email, in Safety Recommendation P-19-11, the NTSB recommended that Washington Gas “[e]stablish a time frame with specific dates and milestones for the replacement of mercury service regulators throughout the Washington Gas network that recognizes the need to expedite this program and that prioritizes multifamily dwellings where mercury service regulators are located inside the property.” The Company’s response and status report regarding the removal and replacement of mercury service regulators (“MSRs”) for each of the three jurisdictions in which it operates follows below. In sum, consistent with Safety Recommendation P-19-11, Washington Gas has undertaken aggressive Mercury Service Regulator Replacement Programs (“MSRRP”) in Maryland, the District of Columbia and Virginia. The Company has achieved a significant number of MSR replacements since the system-wide MSRRP was launched in 2021. MARYLAND On December 18, 2020, the Maryland Public Service Commission (“MD PSC”) approved Washington Gas’s proposed 2020 MSRRP (“MD MSRRP”).1 Footnote 1: Case No. 9622, Investigation of Washington Gas Light Company Regarding a Building Explosion and Fire in Silver Spring, Maryland on August 10, 2016, Order No. 89680 (Dec. 18, 2020). The MD MSRRP includes several best-efforts components 2 to ensure replacement of MSRs at multifamily (“MF”)3 and non-multifamily (“NMF”)4 locations in the Company’s Maryland service territory. Footnote 2: “Best effort” recognizes there likely will be instances in which the Company cannot gain access to a multifamily dwelling or will encounter other circumstances beyond its control. Footnote 3: “Multi-family” means service applicable to any multiple-dwelling building or project comprised of four or more dwelling units (apartments) supplied through one meter or a battery of meters. See, e.g., Washington Gas Light Company – Maryland, P.S.C. Md. No. 6, Original Page No. 54, G.S.P. 1A (available at https://www.washingtongas.com/billing-and-payment/billing-tariff-rates-schedules/maryland-tariff-info). Footnote 4: “Non-multi-family” means dwellings that are not multi-family, i.e., dwellings comprised of three (3) or fewer meters. The Company’s goal was and remains to prioritize replacement all MF MSRs within three (3) years of the end of a one (1) year survey of MF locations (i.e., by March 2025). The Company’s goal was and remains to replace all NMF MSRs within five (5) years of the end of the one (1) year survey of NMF locations (i.e., by March 2029). In addition to replacement activities encompassed in the MD MSRRP, Washington Gas continues to replace MSRs when discovered, e.g., through its accelerated pipeline replacement program (STRIDE 5 ) and regular construction activity (known as “betterment”). Footnote 5: See Case No. 9708, In the Matter of Washington Gas Light Company’s Application for Approval of a New Gas System Strategic Infrastructure Development and Enhancement Plan and accompanying Cost Recovery Mechanism, (available at https://webpscxb.psc.state.md.us/DMS/case/9708). Maryland Replacement History and Status • During Calendar Year 2020 and the first quarter of Calendar Year 2021 Washington Gas successfully worked with existing contractors to replace MSRs from a smaller population of higher-confidence locations where the Company believed MSRs exist. 6 Footnote 6: Washington Gas correlated the time period in which MSRs were deployed in the Company’s service territory—from approximately the late 1930s through the late 1960s—with home construction records to develop its “higher confidence” designation. MSR replacement data compiled through 2020 suggested there is a higher probability that an MSR was installed at a newly built home during that period. • On November 19, 2020, Washington Gas awarded a MSR survey-only contract to Heath Consultants Incorporated (“Heath”). Heath was tasked with hiring and training technicians to conduct field surveys of MF and NMF locations. • The MD MSRRP formally started on March 1, 2021, with Heath initiating a one (1) year survey of potential MF locations. • As of March 2024, the Company completed 100% of MF MSR replacements in Maryland. 7 Footnote 7: See Confidential Attachment A – MD PSC Case No. 9662, Washington Gas Annual MSRRP Report (Feb. 10, 2025). This was substantially ahead of the March 2025 target set by the MD PSC in Order No. 89680. • Washington Gas and Heath continue to survey NMF locations in Maryland. The Company has advised the MD PSC and its Staff of continuing “Cannot Gain Access” or “CGA” circumstances. Data on CGA issues is reflected in Washington Gas’s Annual Report to the MD PSC.8 Footnote 8: Id. The Company is working with MD PSC Staff and local governments on CGA protocols. • Beginning April 1, 2025, the Company began notifying customers at NMF premises that, in the event the Company cannot gain access to the premises to remove and replace a suspected MSR, the customer may face service shut off until the regulator can be removed and replaced. To date, no CGA customers have been shut off, nor have any been notified of potential shut off, as a result of being designated as a CGA customer. • Subject to CGA resolution, the Company is on track to remove/replace all NMF MSRs by its internal target of March 1, 2029. Based on an average “find rate” of 43%, the Company estimates there are approximately 8,000 NMF MSRs to replace by its target date. DISTRICT OF COLUMBIA On August 14, 2020 the Public Service Commission of the District of Columbia (“PSC of DC”) approved Washington Gas’s Updated Implementation Plan (“DC Plan”).9 Footnote 9: Formal Case No. 1157, In the Matter of the Investigation into Washington Gas Light Company’s Compliance with the Recommendations of the National Transportation Safety Board, Order No. 20608 (Aug. 14, 2020). The Company’s DC Plan follows the PSC of DC’s directives in Order No. 19982 which, in turn, is based on an email from the NTSB to the Chairman of the PSC of DC.10 Footnote 10: Email Letter from NTSB to the Chairman of the Public Service Commission of the District Columbia (June 10, 2019). As with its MD MSRRP, the Company’s DC Plan and companion DC MSRRP prioritize surveying all accessible and identified MF dwellings 11 that may utilize a mercury service regulator in the District of Columbia, originally estimated at approximately 830 potential locations, within one (1) year after the start of the DC MSRRP, with replacements concluding three (3) years later. Footnote 11: For purposes of the DC Plan and DC MSRPP, “multifamily” was determined according to the District of Columbia Office of Tax and Revenues’ record of Building Type, which is based on D.C. Code § 47–813 (improved and occupied multifamily residential real property which is used exclusively for non-transient dwelling purposes). In addition, the DC MSRRP calls for replacement of NMF MSRs within five (5) years of the conclusion of the NMF survey. In addition to replacement activities encompassed in the DC MSRRP, Washington Gas continues to replace MSRs when discovered, e.g., through its accelerated pipeline replacement program (PROJECTpipes) and regular construction activity (known as “betterment”). District of Columbia Replacement His

Addressee Organization Type: P-Private Industry

Communication Date: 2025-05-22

Communication Type: Official Correspondence

Communication Contents: -From John C. Dodge, Associate General Counsel and Director, Regulatory Matters: By letter dated April 15, 2025 Washington Gas Light Company (“Washington Gas,” “WGL,” or “Company”) responded to your March 24, 2025, email inquiry regarding Safety Recommendation P-19-11 issued on June 10, 2019, by the National Transportation Safety Board (“NTSB”). The purpose of this Supplemental Response is to update the Virginia section of the Company’s report, indicated by yellow highlighting below: VIRGINIA Virginia Replacement History and Status • As of December 31, 2024, the Company completed 10,129 mercury service regulator (“MSR”) replacements in Virginia. Footnote 1: See Attachment C – VA SCC Case No. URS-2021-00286, Washington Gas Quarterly Status Report on AMRRP Report (Jan. 13, 2025). • As of the Company’s April 15, 2025 Response to the NTSB, Washington Gas had replaced 229 multi-family (“MF”) MSRs since initiating the Accelerated MSR Replacement Program in March 2021, or 97% of the known MF MSRs. • In its letter dated April 15, 2025 to the NTSB the Company noted that it “has made multiple attempts to gain access to the remaining six (6) known MF MSR locations to replace the MSRs there and will continue to do so.” The correct number of remaining MF MSRs as of December 31, 2024 should have been reported as two (2). The Company further notes that, as of May 15, 2025, the remaining two (2) MF MSRs have been replaced or remediated. Accordingly, the Company has replaced 100% of known MF MSRS in Virginia. Finally, the Company is providing a copy of its revised report for the fourth quarter of 2024 filed at the Virginia State Corporation Commission in Case No. URS-2021-00286, which also reflects the updated Virginia data. Please direct any questions regarding this matter to the signatory below.

Addressee Organization Type: P-Private Industry

Communication Date: 2020-04-10

Communication Type: Official Correspondence

Communication Contents: We note that you were working on a schedule with each of your three public service commissions that includes prioritizing multifamily dwellings. Pending establishment of the program with specific dates and milestones, Safety Recommendation P-19-11 is classified OPEN--ACCEPTABLE RESPONSE.

Addressee Organization Type: P-Private Industry

Communication Date: 2020-08-06

Communication Type: Official Correspondence

Communication Contents: We note that you have developed a Mercury Regulator Replacement Plan (MRRP), which expedites mercury service regulator replacement and prioritizes multifamily dwellings. You have filed the MRRP with each of your public service commissions (PSCs), and have issued a request for proposal to complete the work. Pending PSC approval of and commencement of work on your MRRP, Safety Recommendation P-19-11 is classified OPEN--ACCEPTABLE RESPONSE.

Addressee Organization Type: P-Private Industry

Communication Date: 2025-09-26

Communication Type: Official Correspondence

Communication Contents: Our investigation found that the failure of a mercury service regulator, combined with an unconnected vent line, posed a significant threat to people and property and gave little warning of the impending failure. Further, mercury service regulator failure risk increases with age. As noted in our August 6, 2020, letter, this recommendation would remain open pending public service commission approval and commencement of work on your Mercury Regulator Replacement Plan (MRRP). We understand that Washington Gas developed and is implementing an MRRP that was approved by the Virginia, Maryland, and District of Columbia service commissions. We are pleased to learn that nearly all the known mercury service regulators in mutifamily buildings in all three jurisdictions have been replaced. Additionally, the commissions continue to oversee regulator replacement in non-multifamily buildings within their respective jurisdictions. This action meets the intent of this recommendation. Accordingly, the Board has voted to classify Safety Recommendation P-19-11 CLOSED-- ACCEDPTABLE ACTION. Thank you for your commitment to safety.