In disaster management, emergency services agencies such as police forces, are growingly using social media microblogging services as an additional channel to distribute information to the general public. How these emergency services agencies are using these social media channels is still insufficiently understood. This paper introduces Actor-Network-Theory as a means to understand the emergency services agency social media utilisation. Using the case of the Boston Marathon 2013 Bombing, we apply genre analysis in interpreting the Boston Police Department’s social media communication to understand whether the disaster typology or the used social media channel have an influence on the microblogging utilisation of the emergency services agency. The findings imply that both the used social media channel and the specific characteristics of a disaster have an influence on how a social media channel is used.