Safety Investigation of CNG Leaks In Enclosed Parking Structures - Computational Fluid Dynamics Modelling and Analysis

At Transport Canada's request, the National Research Council of Canada (NRC) examined potential safety issues related to leaks from natural gas Class 2 trucks in Canada. This work involved performing a literature review in order to establish the required parameters to perform computational fluid dynamics (CFD) simulations of different leak scenarios of Class 2 compressed natural gas (CNG) vehicles inside parking garages. The literature review consisted of determining the following:

  • The typical size of the parking enclosure for typical fleets of Class 2 trucks such as the bi-fuel GMC Sierra 2500, Dodge Ram 2500, and Ford F250;
  • The failure modes that result in a leak, the size and duration of the leak, and the likelihood of a leak for CNG and hydrogen (H2) vehicles; and
  • The likelihood of explosion vs. fire.

To compare the relative risks of CNG vehicles versus hydrogen gas vehicles, it was decided to also simulate a leak from a hydrogen vehicle (the flammable and explosive cloud size and duration from a PRD release of a CNG vehicle was compared with that of a hydrogen vehicle). The hydrogen explosive clouds formed by PRD releases inside medium and large size garages are smaller than that of methane PRD releases. However, hydrogen ignition is more likely because the ignition energy is lower.

This report contains a complete description of the two selected parking structures and modelling scenarios, including a description of all assumptions and limitations. The modelling scenarios include different leak rates, duration of leaks and temperature effects.

The full report can be found at: