There is general consensus that critical mass at inception ensures the sustained success of online communities. However, no clear understanding of what constitutes such a 'critical mass' exists and too few quantitative studies have been conducted into the relationship between initial online community interaction and its longer term success to draw any conclusions. In this paper we start to address this gap through a large-scale study of the relationship between IRC chat channel survival and initial chat channel community interactions. A sample 282 chat channel births was used for survival analysis which explored the relationship between the overall user activity in each channel at its inception and the channel's life expectancy. Significant relationships were observed between online community lifespan and critical mass measures: 1) message volume, 2) user population heterogeneity and 3) production functions. The results lend support to the Critical Mass Theory of collective action.