"An Incident Commander's responsibility is to assess or 'size-up' the emergency situation to get a good understanding of the problems, issues and concerns and to achieve the needed situational awareness. If the incident is going to grow to where a Unified Command structure is required, it is often helpful to write down the problems that each unified agency identifies as needing attention. This process often alleviates some of the resistance that occurs when trying to unify command among fire, law, public works, Emergency Medical Services, health and the other agencies represented."
Coffee Break Training - Command and Control Series No. CC-2013-5
United States Fire Administration: http://www.usfa.fema.gov/