JOHN YANG: The head of Maui County's Emergency Management Agency resigned earlier this week amid criticism of his decision not to activate warning sirens during the deadly fast moving wildfire.

He said he was quitting for health reasons.

The fire and the high death toll have put a spotlight on how communities respond to all sorts of emergencies, both natural and manmade.

Tricia Wachtendorf is director of the Disaster Research Center at the University of Delaware.

Tricia, how significant was that or how big a factor was that decision not to use the sirens in the high death toll that resulted?

TRICIA WACHTENDORF, University of Delaware: I want to start off by saying, of course, how tragic this event is.

And I think all of our hearts just go out to not only the survivors of this just devastating disaster, but also the emergency responders.

One of the things that we know very clearly from decades of research on disasters is that there is a sequence of behaviors that people need to go through before they even begin to start reacting to a disaster or to a warning.

They have to hear it.

They have to understand it.

They have to believe it.

They have to personalize it.

So is this actually me that one is talking about?

And they have to confirm it.

And that can be with people in their household.

It can be calling up a friend or a family member.

It could be checking on the Internet and trying to find out, is this something that I need to do some action, protective action toward.

So anything that can speed up that decision making to get them to that point, be it using different ways to reach people through cell phone, through the media, through sirens, through other kinds of warning mechanisms gets people just a little bit more closer to be able to start that very time consuming step of actually evacuating or taking protective action.

JOHN YANG: Well, in the Southwest now, they've got a tropical storm, it's currently a Hurricane Hilary bearing down on them, and they're already warning about potentially catastrophic and deadly flash flooding over the next 36 hours or so.

Flash flooding is something that, by definition, comes on very quickly.

What's the best way to warn people about that?

TRICIA WACHTENDORF: The more advanced notice that you can give people to be on guard, to be ready for an evacuation, the better.

The fact that it takes some people much more time to get to that point.

They may have a mobility issue.

They may not be able to get out of an area because they don't have transportation.

So having that advanced warning gets people thinking.

They get people talking about this to each other.

And then when there is a warning that comes through, they're much more close to the point of actually reacting.

Those seconds, those minutes really count.

JOHN YANG: The Maui County emergency manager said that the reason he did not sound the sirens is because they were intended, he said, for tsunamis, and he didn't want people rushing inland, perhaps toward the fire.

What do you make of that explanation?

And can emergency responders afford to have a one alert system for one particular event?

TRICIA WACHTENDORF: There's a few things at play there.

One, there's sometimes a misconception that people will panic during a disaster, that there will be widespread panic that takes place that's not backed up by the data unless there is a window of opportunity for escape that's quickly closing.

It's actually more difficult to get people to move, to start taking action.

That's why those extra minutes and hours count so much.

It will be really important to look at the plans that are in place for that part of Maui.

Whether or not community residents believe that those sirens are something that should be used for all different types of hazards, whether or not there was a failure to activate them, and they should have been, whether or not there were repairs that needed to be done.

So I think part of the real investigation that will happen is the extent to which how much this was decision making and how much it was a lack of planning or different types of planning that didn't take into account the severity or the quick onset of this particular fire.

JOHN YANG: If you were designing a warning system from scratch, someplace that's never had one before, and they called you and asked you to do it, what would it look like?

TRICIA WACHTENDORF: It would, first of all, involve the input of that community and understanding the very different types of community members that are in place.

You can't design a warning system for a community.

It really has to be with them.

It might be fine for an official to say that this is what we use particular warning mechanisms for, but if a community has a different understanding of that warning system isn't going to be effective.

There are residents in this community.

There are people who've lived there for a long time, for a short time.

There are tourists who are in the area, people who commute back and forth.

All of those will have a different response and understanding to those warning strategies.

And we also know that we have to use a multipronged approach.

So it can't just be sirens, it can't just be cell phone or media.

Different kinds of channels of communication reach people in different ways.

People trust different sources of information.

All of that needs to be taken into account, not simply when that hazard is threatening people immediately, but thinking about those plans years in advance.

JOHN YANG: You mentioned trust.

I would suspect some people in Maui may not -- may have lost trust in the government emergency response.

How do they rebuild that?

TRICIA WACHTENDORF: The recovery process is extremely challenging at the best of times.

This community has a long road ahead, unfortunately, in thinking about the amount of paperwork that's involved, the claims that have to be filed, trying to make sense of the financial and the community aspects, when you add that element of blame and mistrust, it can be a real challenge.

And they really will need our support in moving forward.

JOHN YANG: Tricia Wachtendorf from the University of Delaware.

Thank you very much.

TRICIA WACHTENDORF: Thank you.