NFPA Today - September 03, 2020

Just Weeks After Fatal Baltimore Explosion, Fire Protection Research Foundation Releases New Research on Combustible Gas Dispersion and Detector Location Analysis

gas explosion snipAccording to research from NFPA, an estimated 4,200 home structure fires and an average of 40 deaths result annually when natural gas is ignited.

The devastating outcome of a combustible gas leak within a residence was on full display recently when three rowhouses in Baltimore exploded, killing two and injuring seven. While gas detector placement information is available within manufacturer recommendations, NFPA does not currently have a standard containing more specific prescriptive-based detector placement requirements supported by technical review.

NFPA 715, Standard for the Installation of Fuel Gases Detection and Warning Equipment, however, is currently in the early developmental stages prior to beginning full public review. NFPA 715 will help to minimize tragic incidents like we saw in Baltimore on August 10th and in the Merrimack Valley region of Massachusetts last year when a series of more than 80 explosions and fires occurred in approximately 40 homes, killing one and forcing 30,000 to evacuate their residences. NFPA 715 will cover the selection, design, application, installation, location, performance, inspection, testing, and maintenance of fuel gas detection and warning equipment in buildings and structures.

The Fire Protection Research Foundation, the research affiliate of NFPA, recently completed a report studying combustible gas leaks and dispersion in residential buildings, as well as an analysis of combustible gas detector placement to provide the necessary technical basis to justify the requirements in NFPA 715.

Computer modeling was used to quantitatively evaluate the impact that placement has on gas detector performance in residential occupancies. Natural gas and liquefied petroleum gas releases were simulated in different residential structures, and gas concentrations were tracked at numerous potential detector locations within these buildings to determine which locations are most effective for reliable and early detection. Overall, more than 250 simulations were performed with a wide range of plausible leak types and environments to produce the most robust technical basis upon which gas detector location recommendations can be made.

A hazard-based approach was also applied to understand the performance of gas detector installation locations, specifically looking at (1) the role that detector location plays in detecting leaks before certain hazardous conditions arise and (2) the ability for the detector to provide sufficient response time prior to any hazardous conditions arising.

The study highlights the importance of requiring a gas detector in the same room as permanently installed fuel-gas appliances. For these detectors, generally better performance was observed when: the detector was placed closer to the leak source, there was an unobstructed path between the detector and the leak source, and when the detector alarm threshold was lower (i.e., 10% Lower Flammability Limit (LFL) compared to 25% LFL). Poorer performance was observed when a detector was located: near HVAC supply registers; near passive openings such as doors and windows; and near openings to adjacent areas (e.g., door openings and stairwells).

The final report describing the entire study can be found on the hazardous materials page under gases. To learn more about dozens of Fire Protection Research Foundation projects currently underway, click here.

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Sreenivasan Ranganathan
Director, Research Foundation, Mission to plan, manage and communicate research in support of the NFPA mission

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