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Estimation of Protective Distance/Threat Zone

Get the Estimation Tools

1. Protective Distance - Download and install WISER on your computer
2. Threat Zone - Download and install CAMEO on your computer


Sample protective distance image from WISER

What is Protective Distance or Threat Zone?


Releases of hazardous substances into the air can occur from transportation and other types of accidents, and from deliberate efforts. These types of releases into the air can pose risks to the general public and response personnel. The Department of Transportation (DOT) Emergency Response Guidebook (ERG) includes protective distance information for substances, defined as the area likely to be affected during the first 30 minutes after a substance is spilled.

Similar to a protective distance, a threat zone indicates the geographical area in which an atmospheric release of a substance would impact a given area during a specified time frame. Also, as defined in ALOHA, a threat zone is an estimated area where a hazard (such as toxicity, flammability, thermal radiation, or damaging overpressure) has exceeded a user-specified Level of Concern (LOC).



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About the DOT ERG


The Emergency Response Guidebook, currently available as the 2012 version (ERG2012), was developed jointly by the US Department of Transportation, Transport Canada, and the Secretariat of Communications and Transportation of Mexico (SCT). It is designed for use by firefighters, police, and other emergency services personnel who may be the first to arrive at the scene of a transportation incident involving a hazardous material.

The ERG is primarily a guide to aid first responders in:

  1. quickly identifying the specific or generic classification of the material(s) involved in the incident, and
  2. protecting themselves and the general public during this initial response phase of the incident. The next version of the ERG is scheduled for release in 2012.


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About WISER and Its Use of Protective Distance


The WISER (Wireless Information System for Emergency Responders) from the National Library of Medicine can assist first responders in hazardous material incidents. It provides a wide range of information, including substance identification support, physical characteristics, human health information, and containment and suppression advice.

Since Version 4.2 in 2008, WISER for Windows has included the capability for a substance's protective distance data to be overlaid on an interactive map. Protective distance mapping will be added to WebWISER and other WISER platforms in the future. Once the substance is selected in WISER for Windows, the "Map Protective Distances" button provides access to this feature (Internet connectivity is required). The WISER User's Guide provides details about this feature. The "Protective Distance" in WISER represents the areas likely to be affected during the first 30 minutes after a substances is spilled, and follows the DOT Emergency Response Guidebook approach.

To determine the appropriate area to clear out, selecting the Protective Distance option from the data menu brings up the evacuation distance information from the DOT Emergency Response Guidebook (ERG). The ERG is also accessible in its entirety by selecting the Hazmat submenu.



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About CAMEO and Its Software Suite


CAMEO initially was developed because NOAA recognized the need to assist first responders with easily accessible and accurate response information. Since 1988, EPA and NOAA have collaborated to augment CAMEO to assist both emergency responders and planners. CAMEO has been enhanced to provide emergency planners with a tool to enter local information and develop incident scenarios to better prepare for chemical emergencies. The Bureau of Census and the U.S. Coast Guard have worked with EPA and NOAA to continue to enhance the system.

Who uses CAMEO?

  • Firefighters
  • State Emergency Response Commissions (SERCs) and Tribal Emergency Response Commissions (TERCs)
  • Local Emergency Planning Committees (LEPCs)
  • Industry
  • Schools
  • Environmental Organizations
  • Police Departments

The CAMEO software suite includes four core programs, CAMEO, CAMEO Chemicals, ALOHA, and MARPLOT, which can be used together or individually. When used together, the programs interact seamlessly and information can be linked easily between them. In addition to these four core programs, there are a variety of other programs that can be used with the CAMEO software suite.

CAMEO Software Suite

  • CAMEO - A database application that includes several modules (such as Contacts and Facilities) to assist with data management requirements under the Emergency Planning and Community Right-to-Know Act (EPCRA). This program can also be used to navigate between ALOHA, MARPLOT, and the downloadable version of CAMEO Chemicals.
  • CAMEO Chemicals - A program that allows users to search for chemicals in the CAMEO chemical database, print customized reports with response recommendations, and find out how chemicals would react if they mixed. This program is available as a website and as a downloadable program; however, only the downloadable version can share information with other programs in the suite.
  • ALOHA - A modeling application that estimates threat zones associated with hazardous chemical releases, including toxic gas clouds, fires, and explosions.
  • MARPLOT - A mapping program with which users can easily view and modify maps, and users can also create your own objects.

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CAMEO's ALOHA - Areal Locations of Hazardous Atmospheres


Key Features

  • Can generate a variety of scenario-specific output, including threat zone plots, threat at specific locations, and source strength graphs.
  • Can calculates the rate of release for chemicals escaping from tanks, puddles (on both land and water), and gas pipelines and predicts how that release rate changes over time.
  • Ability to models many release scenarios: toxic gas clouds, BLEVEs (Boiling Liquid Expanding Vapor Explosions), jet fires, vapor cloud explosions, and pool fires.
  • Ability to evaluates different types of hazard (depending on the release scenario): toxicity, flammability, thermal radiation, and overpressure.
  • Can displays threat zones on MARPLOT maps (and on ArcView and ArcMap with the Arc Tool extensions).
  • It works seamlessly with companion programs CAMEO Chemicals and MARPLOT; it can also be used as a standalone program.


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CAMEO's MARPLOT - Mapping Application for Response, Planning, and Local Operational Tasks


Key Features

  • Ability to switch quickly between three basemaps: standard map files, aerial photos, and topographical maps.
  • Can get population estimates.
  • Can get information about basemap features.
  • Can link overlay objects to the CAMEO database program.
  • Can easily display ALOHA threat zones.
  • Can customize your view by drawing your own objects on the map and specifying which basemap layers are shown.


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Additional Resources

  1. Brown DF, Dunn WE. Application of a quantitative risk assessment method to emergency response planning. Computers & Operations Research,2007. 34(5): 1243-1265. (This approach is used for the DOT's Emergency Response Guidebook's protective distances).
  2. Henry K, Silva J. Enhanced Consequence Management, Planning and Support System (ENCOMPASS). Enabling an effective, coordinated response. Emerg Med Serv. 2002 Apr;31(4):52-9. [PubMed Citation]