The purpose of this paper is to estimate impacts of flammable plume mass following an accidental release from a compressed natural gas (NG) pipeline. Three cases are considered. The first case involves the accidental release of NG inside a building. The second case involves the accidental release of NG directly into the atmosphere. The third case evaluates the potential for an outdoor released NG plume to be trapped inside a building located downwind of the release source. Although the final goal is to estimate overpressures on nearby buildings induced by an explosion, the paper will focus on the process of determining the release rate, plume rise, and dispersion of the source term along the plume path.

Release rates estimated by the traditional Bernoulli flow equation are usually too conservative and not representative of the real world scenarios. Therefore, this paper takes into consideration the isentropic expansion occurring between the main transmission line and the branch pipeline, and the friction factor exerted by the steel pipe, and the change of the pipe size. For an indoor release, stoichiometric combustion of NG is considered. For a release in an unconfined environment, the flammable mass is estimated from the volume integration of a puff between the lower and upper flammable limits.

For comparison purposes, an independent analysis performed by a computational fluid dynamic model is discussed in order to evaluate the validity of the approach used for the dispersion of the flammable mass.