In terms of key facts needed to guide the assessment process, I would assert that determining the numbers and nature of the wounded would be the next most important thing to assess in addition to determining how to help the victims.

If a building collapsed can the proper construction tools be obtained to clear debris?  If there was a nuclear incident are the correct medicines and treatments available?  Understanding the type and number of materials needed for treatment would be my next step after ensuring the safety of the first responders.

One paramount first task is to assess the further dangers. If a building is about to blow sky high because of a gas line leak or a fire in electrical circuits or petrol-fuel being leaked, the first task is to learn this, otherwise, all other efforts become irrelevant.

I would second the initial action of gauging the injuries of those involved in the disaster. I would suggest the next thing would to be to survey the scene (if there are gas leaks, electrical wires, or fires). After that, the scene would need to be protected (to insure that no one else is injured). Searches for survivors would need to be taken care of next .

The nature of a disaster is such that there can't be a specific set of criteria that can be used "to gauge the severity of the incident." Every disaster presents its unique set of circumstances; in the aftermath of such an event, the immediate need is to assess the situation and start meeting needs. The severity of the incident can be rated later, when the crisis has been mitigated.

After doing initial evaluation and determination of the safety of addressing those in immediate need, resources to help in addressing those needs should be contacted and brought in as and where required. Coordination of help efforts becomes an important issue at this point, but it is often difficult to carry out an organized plan for relief efforts due to the urgency of the circumstances being addressed.

I agree that the first step is to assess the security of the area and perhaps the likelihood of a recurrence.  You will need to determine if people can be assisted where they are or if evacuation would be more prudent.  For instance, an earthquake is likely to have after shocks so people should be moved to a secure location away from damaged buildings and rubble.  A tornado is usually a single occurrence.  Once the storm has passed, the danger is over.  People can be treated where they are instead of needing to be moved.

Once you determine if the area is secure, you can begin treating victims.  Triage is an important step in disaster evaluation.  The critically injured must be treated first to ensure the maximum number of people can survive the incident.  Supplies and personnel will need to be divided into teams and complete their tasks independently.  For instance, there might be a medical team and a recovery team.  The recovery teams would be searching for injured among rubble or homes while the medical team treats the injured that are found.

I think the first step one should follow when assessing an emergency situation is to determine if there is still a risk to the people who may begin assisting the victims or infrastructure.  You can't help anybody through an emergency if you fall victim to the same circumstances that started the problem.

initial activities to support a valid situational assessment under terrorist and other scenarios. What steps would you follow to assess an emerging disaster situation? What are the key facts that need to be captured early to guide the assessment process? What criteria should be considered to gauge the severity of the incident? What would be the likely impact of mistakes made during the situational assessment process?

I think that the most important first step in responding to potential terrorist activity is to secure the area.  This might mean ensuring that suspects cannot leave and there is a way to differentiate them from victims, but also ensuring that there is no more danger.  Immediately evacuating a building, for example, is a good move but you have to ensure that you can contain the occupants in order to determine if any of them are involved in the threat.

initial activities to support a valid situational assessment under terrorist and other scenarios. What steps would you follow to assess an emerging disaster situation? What are the key facts that need to be captured early to guide the assessment process? What criteria should be considered to gauge the severity of the incident? What would be the likely impact of mistakes made during the situational assessment process?

Key facts would include the extent of the damage, whether the attack was still ongoing, whether additional risks were created (like ruptured gas lines, collapsing buildings, etc.) I think that initially, the criteria used to gauge the severity would be the number of people injured or killed. The likely impact of mistakes, unfortunately would be that more people would die or that rescue personnel would walk into a situation that placed their lives in jeopardy unnecessarily.