The UK Emergency Services (ACPO 2009, 2010) views interoperability in terms of voice communications between equivalent layers of command, in response to exceptional circumstances (i.e. major incidents) that do not normally impact upon existing separate C2 structures. As such, the communications merely replaces the multiagency huddles that are seen during the consolidation phases of major incidents with a shared talk group. Thus, the initial response phase of incidents will still be co-ordinated entirely separately through the existing C2 systems of each service. As we noted in Chapter 11, this view of interoperability is drawn from the US Department of Homeland Security model and is, we believe, fairly representative of the view of communications in emergency response internationally. From a sensemaking perspective, this approach to interoperability makes a number of assumptions regarding the nature of major incidents:

• That it will be obvious when an incident is a major incident • That it will be obvious what the nature of the incident is • That it will be obvious what information needs to be exchanged • That the exchange of non-voice data between services is not

critical to effective incident co-ordination

As we have noted in Section 1.1.1, these assumptions may often be the exception rather than the norm, and this means that a critical initial phase of any incident response lies in the challenge of determining what is happening. We see this challenge as the primary domain in which sensemaking occurs (although if the situation should radically shift, then a new phase of sensemaking could take place).