Washington State offers several programs for emergency volunteers:
Temporary Emergency Workers, and Registered Emergency Workers. These are covered in Chapter 118-04 WAC. Fortunately for all of us, Michael and Catherine Cochrane dug into this issue and spotted a number of issues - which have since been rectified - and they will hopefully provide a summary of the requirements and resources of interest to REWs here in the future.
Liability issues are also covered in RCW 38.52.198.
Emergency Law Inventory
University of Pittsburg's Emergency Law Inventory Resource reviews WA state's credentialing and liability requirements: LegalInventory.pitt.edu