4.1. Evacuation/Sheltering

Depending on the nature of the chemical incident, people in the affected area may need to evacuate or shelter-in-place at a specific location to prevent them from being exposed and/or contaminated. A successful evacuation removes people from the affected area and avoids exposure to the released chemical. (An example is the evacuation of area populations following a chlorine release described in the Prologue.¹²) During shelter-in-place, people seek shelter inside a building and remain inside until the danger passes. Making the decision to recommend sheltering or evacuation is one of the most important and potentially consequential decisions facing local emergency officials following a toxic chemical release. The decision is often not easy to make, even when relevant information is provided by RPs, and generally must be made quickly, even when all relevant information is not available. The decision to have a population evacuate vs. shelter-in-place revolves around two key questions:^25,62

• Will shelter-in-place provide adequate protection, preventing people from receiving a harmful exposure to the chemical?
• Is there time to evacuate before the chemical plume reaches the area?

The answers to these questions depend upon a number of factors that contribute to the effectiveness of either protective action, including:

• The identity and amount of the chemical released, and its degree of health hazard and containment
• The chemical’s location and rate of movement
• Locations and populations of projected areas affected at time of day of release
• The time until the hazard is projected to reach and clear each affected area
• How long the implementation of protective actions will take, including evacuation and/or shelter-in-place, and including considerations for family reunification (e.g., if children are in school or daycare, etc.)
• The availability of and degree of protection offered by local housing and buildings (i.e., their ability to be “sealed” from outside air)
• Traffic, and inclement weather or road closures that may impede evacuation
• Current or impending weather conditions that might affect chemical movement or the safety of sheltering-in-place

Unfortunately, a simple technical decision-making method for choosing protective actions does not exist as the circumstances and the relative importance of the factors listed above will vary with each release scenario. Further, information critical to decision-making is likely to be uncertain or incomplete, particularly early on in the response. In general, sheltering-in-place is best used when evacuating the public would cause greater risk to them than staying where they are, or when an evacuation cannot be performed due to time or other constraints. However, sheltering can have negative consequences if shelters are leaky, people are not advised when it is safe to leave the shelter, or the release continues for an extended period of time. Evacuation may be preferable when the substance released includes flammable vapors, the substance will linger for a long time in an area, or buildings cannot be closed tightly enough to provide safe shelter. Evacuation can have negative consequences if the population of the affected area is caught outdoors or in their vehicles when contamination enters the area.

For any particular release, a combined response may be called for, with sheltering-in-place recommended for areas close to the release and in the possible path of contamination, and evacuation recommended for areas that have more time before possible exposure to the chemical. Protective action advice may differ for urban vs. rural areas. While urban areas are likely to have many more people in the area at risk, due to their high population densities and the short response times often required, their rapid evacuation may be impractical. However, in an urban area, buildings can provide considerable protection against an outdoor cloud of toxic chemicals, particularly for reactive chemicals like chlorine. Thus, a temporary shelter-in-place may be the safest course of action for a densely packed public, especially in incidents in which there are only a few minutes to protect people. In contrast, rural areas are likely to have relatively few people within a risk area, so evacuations can proceed more smoothly.

Overall, jurisdictions should consider shelter-in-place as the first/default option, when feasible, as it has reduced costs, resource requirements, and negative impacts than evacuation. Yet if extended (multi-hour) sheltering is being considered, authorities should work to ensure sheltered individuals have adequate food, water, sanitation, medical care, and protection from the elements (see also KPF 5, Augment Provision of Mass Care and Human Services to the Affected Population).⁶³

Evacuations represent a sweeping course of action, and decisions to evacuate cannot be made lightly; evacuations cannot be carried out effectively without preplanning. Plans should be developed that clearly identify under what circumstances evacuation would be appropriate and necessary. Evacuation plans should:

• Identify how instructions will be effectively communicated to the public
• Identify how people and animals will be moved (i.e., by city buses, police cars, private vehicles, other)
• Make provisions for redirection of traffic
• Identify the location to which students will be moved and how parents will be notified
• Include plans for evacuating hospitals, nursing homes, and homes for the physically or mentally disabled

Implementation of evacuation and shelter-in-place decisions for small-scale incidents are typically handled at the lowest possible jurisdictional level by local incident commanders or public safety officials (e.g., fire chief, police chief, public health official). For community-level or larger-scale events affecting multiple jurisdictions, higher-level authorities such as those exercised by elected officials at the local or state level (e.g., mayor, county executive, judge, governor) are often necessary to issue evacuation orders.

Footnotes

12. National Transportation Safety Board. (2019, February 11). Hazardous Materials Accident Report: Rupture of a DOT-105 Rail Tank Car and Subsequent Chlorine Release at Axiall Corporation, New Martinsville, West Virginia, August 27, 2016. (Report No. NTSB/HZM-19/01).

25. U.S. Department of Agriculture. (2020, June 2). Animal Health Surveillance in the United States. Animal and Plant Health Inspection Service Veterinary Services. ;

62. Department of Homeland Security. (2019, July). Planning Considerations: Evacuation and Shelter-in-Place Guidance for State, Local, Tribal, and Territorial Partners.

63. Federal Emergency Management Agency. (2013). Key Response Factors and Considerations for the Aftermath of a Catastrophic Chemical Incident. P.1013. Print.