- Author
- Geomet Technologies Inc.
- Title
- Hydrogen Emissions From Electric Vehicle Batteries Undergoing Charging in Residential Garages. Final Report.
- Coporate
- Geomet Technologies Inc., Germantown, MD
- Report
- EPRI TR-103421; Project 3272-12, December 1993, 114 p.
- Keywords
- electric batteries | hydrogen | emissions | garages | residential buildings | motor vehicles | transportation | tests | ventilation | airborne concentration | concentration measurement | vents | explosive limit | computation
- Identifiers
- electric vehicle charging; electric vehicles; electric vehicle infrastructure
- Abstract
- Some electric vehicle (EV) batteries emit hydrogen gas (H2) during the latter portion of the charging process. Since H2 is combustible in concentrations as low as 4% in air, EV battery charging in closed settings such as residential garages raises the question of the potential for fire. The rate at which air in a residential garage is exchanged with outdoor air affects the average concentrations of hydrogen, though local accumulations under the EV or near the battery's vent might reach higher-than-average levels. Clarification of the safety risks from H2 concentrations during EV battery charging in residential garages is needed to support the Electric Vehicle Charging Article proposed for the 1996 edition of the National Electrical Code®. To determine the ventilation rate needed in a residential garage to keep H2 concentrations below a hazardous level for a maximum possible EV charging rate. Investigators simulated H2 emissions by the controlled release of hydrogen in a test garage and measured H2 concentration as a function of H2 input rate, garage volume, area of ventilation between the garage and the outdoors, and the overall air exchange rate. Vents, which were centrally located in the cover of the test garage, measured 0, 1, and 6 ft2. Using combustible-gas sensors, investigators also measured H2 concentrations during the charging of six electric vehicles. The air exchange rate was measured by the tracer-gas decay method, where the tracer gas was carbon dioxide. Under well-sealed (no vent) conditions, H2 emissions of a few hundred liters/hr can exceed the lower explosive limit (LEL). Current standards describe a location as "hazardous" if it has a flammable-gas concentration greater than 25% of the LEL. With a 1 ft2 vent, nearly 1000 1/hr would be required to exceed the LEL; with a 6 ft2 vent, emissions of approximately 5000 1/hr would be required to exceed the LEL. Splitting the 1 ft2 vent between the top and bottom of the garage cover resulted in greater ventilation efficiency. This report describes calculations for determining the minimum required ventilation to keep the H2 concentration in enclosed EV charging stations below 1% of the LEL. The variability of natural ventilation presents the possibility that air exchange between a garage and the outdoors could at times be equivalent to that of a well-sealed garage. Because some of the emissions tests conducted under this project experienced air exchange rates well below 0.1 air changes per hour, forced ventilation will likely be necessary for EV battery charging in residential garages.