There is a need for cybersecurity capabilities and features to protect the Nationwide Public Safety Broadband Network (NPSBN). However, cybersecurity requirements should not compromise the ability of first responders to complete their missions. In addition, the diversity of public safety disciplines means that one solution may not meet the usability and security needs of different disciplines. Understanding how public safety users operate in their different environments will allow for usable cybersecurity capabilities and features to be deployed and used. Although first responders work in a variety of disciplines, this report is focused on the Fire Service, Emergency Medical Services (EMS), and Law Enforcement. This report describes the constraints presented by their personal protective equipment (PPE), specialized gear, and unique operating environments and how such constraints may interact with mobile authentication requirements. The overarching goal of this work is analyzing which authentication solutions are the most appropriate and usable for first responders using mobile devices in operational scenarios in the field.