In light of the energy transition, ammonia is seen as an important energy material and carrier. Therefore, the transport of ammonia is expected to grow extensively. Even though transport of ammonia by pipelines is perceived to be the safest option, the high toxicity of ammonia presents significant safety risks in case of a pipe rupture or leakage. Because of its low boiling point, ammonia is expected to pool in the crater, where it may take days or even weeks to fully evaporate. Plans for transport pipelines of ammonia in the Netherlands have therefore raised questions by regulators about their possible risks in a densely populated country. This paper presents the results of modelling of ruptures of ammonia pipelines ranging from 6 to 36 inch diameter. DNVs Safeti-NL was used for the calculations, with the effect modelling split in two. First, the rupture of the pipeline and outflow was modelled. The ammonia outflow occurs within an hour, with a 1% outdoor lethality distance ranging from 440 to 5300 meter, depending on the pipeline length and diameter. Second, the pool evaporation was modelled separately, for both regular pool spreading and a pool in a crater. Both where modelled with various soil types and weather conditions. This results in a 1% outdoor lethality between 60 and 2000 meter, and full evaporation lasting between 6 hours and 15 days. The results of this study can also be used by for example legislators and emergency response planning.