Interpretation Response #26-0015

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date: 05/22/2026

Company Name: Mobile Power Solutions

Individual Name: Rory Pynenburg, Phd

Location State: OR Country: US

View the Interpretation Document

Response text:

May 22, 2026

Rory Pynenburg, PhD
Mobile Power Solutions
9665 SW Allen Blvd
Suite 110
Beaverton, OR  97005

Reference No. 26-0015

Dear Dr. Pynenburg:

This letter is in response to your January 26, 2026 email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to testing requirements for lithium-ion cells and batteries, in accordance with Section 38.3 of the United Nations (UN) Manual of Tests and Criteria. Specifically, you request clarification of the UN Manual of Tests and Criteria, Subsection 38.3.4.8, Test T.8: Forced discharge, as it relates to the definition of "disassembly" and "fire" during testing. You describe a scenario in which, during the rest period following T.8 testing, a pouch cell's envelope burst at a corner, exposing a small, singed protrusion of internal components. You note that no visible flame was observed, and the mesh screen barrier placed 25 cm away was not penetrated. You ask whether this specific result constitutes a test failure.

In accordance with Subsection 38.3.4.8.3, cells meet the T.8 testing requirement if there is no disassembly and no fire during the test and within seven days after the test. Subsection 38.3.2.3 states "disassembly" means a rupture of the cell or battery case where solid components are ejected. However, there is a note to the definition of "disassembly," which states that during cell or component cell testing, ejection of internal components is acceptable provided the energy of the ejected components does not penetrate a wire mesh screen (annealed aluminum wire with a 0.25 mm diameter and grid density of 6 to 7 wires per cm) placed 25 cm from the cell. Based on your observation that the mesh screen remained intact, and the components were merely exposed or protruding rather than forcefully ejected beyond the screen, it is the opinion of this Office that the event described does not meet the criteria for "disassembly." In addition, Subsection 38.3.2.3 states "fire" means that flames are emitted from the test cell or battery. You note that no visible flame was observed. While you state the internal material was singed, in the absence of a visible flame, it is the opinion of the Office this does not constitute a "fire" for the purposes of passing or failing the T.8 test.

Based on your description that there was no disassembly (as defined by Subsection 38.3.2.3) and no visible flame, it is the opinion of this Office that the condition of the cell would likely not constitute a failure of the T.8 test.

I hope this information is helpful. Please contact us if we can be of further assistance.

Sincerely,

Alexander Wolcott
Acting Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division

§ 173.185

Regulation Sections