The U.S. National Institute of Standards and Technology (NIST) conducted a study for CDC to examine the impact of distance of gasoline-powered portable electric generators on indoor CO exposure. The study was based on computer simulations of CO transport outdoors and subsequently within the building and included two phases. The two phases involved multiple simulations of portable generator operation outdoors for a one-story manufactured house and a two-story house respectively. This report presents the second phase of the study using the CONTAM indoor air quality model coupled with two computational fluid dynamics (CFD) models, CFD0 and NIST Fire Dynamics Simulator (FDS), to predict CO concentrations near and within a generic two-story home. In addition to the parameters considered in Phase I, i.e., weather conditions, generator location and distance, this study also considered the effects of the generator exhaust temperature and speed. While it was found that the exhaust temperature and speed may affect CO levels near the house significantly, in general, the results supported the conclusions of the first phase study. In this second phase, it was necessary to locate the generator further than 4.6 m (15 ft) from the two-story house to avoid high indoor CO concentrations. A distance of 9.1 m (30 ft) (the next closest distance modeled) generally resulted in low CO entry indoors, especially with the exhaust pointing away from the house which caused the maximum CO at the house envelope to be only 17 % of that when the exhaust is pointing towards the house. With the exhaust pointing away, the maximum indoor CO level can be reduced to be 3 % of the case with exhaust pointing towards the house under the same wind speed. Therefore, in most cases, to reduce CO levels for the house and conditions modeled in this study, it was helpful to point the generator exhaust away from the house and position the generator at a distance of more than 4.6 m (15 ft).
Technical Note (NIST TN) - 1666
Generator, carbon monoxide, CONTAM, computational fluid dynamics, exposure, indoor air quality, health, multizone airflow model, simulation