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Public Health Emergency Preparedness

This resource was part of AHRQ's Public Health Emergency Preparedness (PHEP) program, which was discontinued on June 30, 2011, in a realignment of Federal efforts.

This information is for reference purposes only. It was current when produced and may now be outdated. Archive material is no longer maintained, and some links may not work. Persons with disabilities having difficulty accessing this information should contact us at: https://info.ahrq.gov. Let us know the nature of the problem, the Web address of what you want, and your contact information.

Please go to www.ahrq.gov for current information.

2. Scenario Inputs

Scenarios are specified on the Scenario Input Page (go to Exhibit 1). You can:

  • Create a new scenario by clicking "New Scenario" on any of the model's pages. Default values are loaded and shown on the page.
  • Modify a previously saved scenario by clicking "Open Saved Scenario," clicking the Browse button on the Open Saved Scenario Page, and navigating to the folder where you saved the scenario.

Exhibit 1: Illustrative Scenario Input Page

Exhibit 1.  Illustrative Scenario Input Page. The screen shot of an input page calls for a name for the scenario; specification of the fleet of vehicles that will be used in the scenario, geographic area, and information about evacuating and receiving facilities.

To run the model, you must enter data about the scenario. The data requirements are described below. Key assumptions that were used in the New York City and Los Angeles pilot tests, which were developed in consultation with city officials, are shown below. These assumptions may provide guidance to users of this model. Go to the companion report, Mass Evacuation Transportation Model: Description for complete details on the assumptions used in the pilot tests.

Scenario Name

You should specify a meaningful name for the scenario, such as "evacuation of Downtown Hospital with 25 percent of the city's ambulances assisting in the evacuation."

Vehicles Used

The model assumes that evacuated persons are transported to receiving facilities on either buses, wheelchair vans, BLS ambulances, or ALS ambulances.

For each of these four types of vehicles, you must specify the following:

  • Number available. The number available should reflect the number that will be used to transport patients from evacuating to receiving facilities, as opposed to the total vehicle fleet size in your jurisdiction. In the New York City and Los Angeles pilot tests, the figures for the ALS ambulances were perhaps the most critical assumption in terms of its effect on the total evacuation time.
    • In New York City, we assumed that 40 percent of the City's ambulances would be assigned to the evacuation, with the remainder saved for other emergencies as they arise during the day; in Los Angeles, we assumed that 5 percent would be assigned to the evacuation.

Tip: The model was designed under the assumption that multiple round trips will be required for each vehicle participating in the evacuation. Thus, the total number of patients that can be moved in a single trip by all vehicles of a particular type should be less than the total number of patients requiring that type of transport. For example, if you specify that 100 buses are available for the evacuation and that each can carry 30 patients, the number of patients that require bus transport (go to"patient transportation needs" below) should be greater than 3000. If this is not the case, you should reduce the number of buses so that each bus must make more than one round trip during the evacuation; otherwise, the model allocates patients to buses inefficiently and the output of the model may be nonsensical. This is usually only an issue for buses and possibly wheel chair vans, but not for ambulances (assuming that ambulances are in short supply).

  • Capacity. Specify the number of patients who can be transported at any given time on the vehicle. Do not include the driver or other medical personnel who have to be on the vehicle during transport.
  • Per patient load time. The time it takes to load a patient into the vehicle can either assume (1) the patient is waiting for the vehicle in the lobby or near the curb or (2) the vehicle driver (e.g., paramedic or EMT) must retrieve the patient from his/her room. The vehicle "unload" time per patient at the receiving facility is assumed to be the same as the vehicle load time.

Evacuating and Receiving Facilities

The model assumes that persons to be evacuated are located in one or more evacuating facilities and that they need to be transported to one or more receiving facilities. If there isn't sufficient room in the receiving facilities, an overflow facility is used (go toOverflow Receiving Facility below).

For each facility, you must specify the following information:

  • Status. On the Scenario Input screen, you must designate a facility as either evacuating, receiving, or not included. Not included means that the facility is ignored when the model is run.
  • Name. Enter the name of the facility.
  • Patient transportation needs. For each evacuating facility, you must specify the percentage of patients in the facility who require each of the four vehicle types (bus, wheelchair vans, BLS ambulances, and ALS ambulances). The percentages should add to 100%. (These data can be ignored for receiving facilities.)
    • In New York City, we assumed that the percentage of patients requiring each vehicle type was the same at all evacuating hospitals and based the percentage on data obtained from six New York City hospitals. The assumptions were: bus—33 percent; wheel chair vans—40 percent; BLS ambulance—13 percent; ALS ambulance—14 percent.
    • In Los Angeles, we obtained a single day's census data from each of the three evacuating hospitals, which included the number of patients in the ICU/CCU, the number on ventilators, and the number on monitors. We mapped those counts into the vehicle requirements, as described in the companion report, Mass Evacuation Transportation Model: Description.
  • Capacity and occupancy rate. Capacity and occupancy together determine the number of persons who will need to be evacuated from each evacuating facility. For receiving facilities, these two figures—combined with the surge capacity figure— determine the number of patients that a receiving facility can accept.
  • Location. For each facility, specify the latitude and longitude (in decimal degrees). This is used to estimate the travel time between evacuating and receiving facilities. If the geographic coordinates of your hospitals are not readily available from local agencies, there are a number of public Web sites that provide the latitude and longitude for a specified address.1

At any time while you are entering input data, you can save the scenario by clicking the Save Scenario button. The inputs are saved in an XML file (go to Section 4).

Tip: Enter all the hospitals in your area once and then save the scenario. You can then reload this scenario each time you run the model and change the status of facilities. For example, you can change a facility's status from receiving to evacuating or from evacuating to receiving. Or, you can change a facility's status to "not included in this scenario."

Tip: If data on your hospitals already exist in an electronic file, it is possible to build the XML file with these data using a spreadsheet, rather than retyping the data into the model (go to Section 4).

You can load a saved scenario into the model by clicking Open Saved Scenario and then navigating to the folder where you previously saved the scenario.

Surge Capacity of Receiving Facilities

You can specify a surge capacity percentage, which will represent the percentage over normal capacity that all receiving facilities can accept in an emergency. For example, a 10% surge capacity at a 400 bed receiving facility that is 90% occupied could receive 80 evacuated patients:

  • 40 additional patients, because it is assumed to be 90% occupied, plus.
  • 40 additional patients, because of the 10% surge capacity.

In both New York City and Los Angeles, we assumed receiving hospitals have a 15 percent surge capacity.

Overflow Receiving Facility Location

The model assumes that patients who cannot be accommodated in the receiving facilities are transported to an overflow facility. You must specify an average travel time to this facility from the evacuating facilities. In reality, the overflow facility could represent several out-of-county locations or an airport where patients will be loaded onto airplanes for transport to another state.

Traffic Congestion Factor and Geographic Area

The model contains a travel time estimator that uses the facility locations to calculate travel times between evacuating and receiving facilities (go tothe companion report Mass Evacuation Transportation Model: Description). The travel times assume an average speed that clearly may not be achievable during a mass evacuation incident. You can increase the travel times by specifying a traffic congestion factor—e.g., 1 is normal speed, 0.5 is twice as fast, and 2 is twice as slow.

The travel time estimator also takes into consideration the population density of the area. Select your area from the drop down list of all Metropolitan Statistical Areas (MSA). If your area is not in the list, select the MSA that most closely resembles your area's population density.


1. For examples, go to http://www.mashupsoft.com/maps/latlonlocator or http://www.batchgeocode.com/lookup/.


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