Incident Complexity: Comparing Industry Tiers and NIMS Incident Types

With a mix of government clients preparing for all-hazards incident management and private sector clients preparing for oil spill response on a worldwide basis, EMSI often gets questions about the relationship between the International Petroleum Industry Environmental Conservation Association (IPIECA) tiered response concept and National Incident Management System (NIMS) Incident Command System (ICS) incident complexity typing. This article intends to distill the concepts of each and compare the two for responders. In short, both are tools to measure and communicate the complexity of an incident.


Tiers are commonly used by members of the oil industry to describe the size and scope of an oil spill response. The oil spill response industry’s Tiered Response Concept was first developed by the IPIECA in the 1980’s, before the oil spill response community implemented ICS, as a means to ensure that appropriate capabilities were available to respond and manage oil spills. The tiered approach to oil spill planning and preparedness, similar to NIMS ICS incident typing, is used by organizations worldwide in developing oil spill response strategies, response team structures, and training and exercise programs. Tiers can also used to describe the complexity of an exercise scenario.

The use of Tiers provides a standard structure from which oil response capabilities can be identified to mitigate any potential spill scenario. There are three components that collectively define the response capability:

  • Response Personnel
  • Equipment
  • Additional Support

This three-tiered structure enables emergency management planners to describe what an effective response to any oil spill, regardless of size or complexity, on land or at sea, would look like. In addition, response resources required are dictated by numerous factors, to include location, oil type, season, and volume. It is the overall impact of the spill, not the quantity of product alone, which dictates the types and amounts of resources required and the duration of cleanup operations. The original concept looked like the graphic to the right.

Updated Tiers Model

Using the Tiered Concept for contingency planning, an assessment of potential incident severity, complexity, and scale of the response is necessary to determine an incident’s tier. While the model was intended to be flexible, it has evolved to better enable emergency managers in the oil spill response community to capture the complex interrelationships between the multitudes of variables of an incident’s response. The key concept to remember in this evolving model is that there are no hard boundaries between tiers. Planners and responders need to evaluate the totality of the event to determine its tier. For example, a medium spill that on the surface is a Tier 2 may rise to a Tier 3 due to geographic isolation that prevents a timely response from local forces. The effect of timeliness of response may create a larger impact of the incident, necessitating a higher Tier designation.

The evolving model is depicted as a segmented circle to represent the diverse capabilities. IPIECA has identified 15 areas of response capabilities for consideration:

  • Surveillance modelling and visualization
  • Offshore surface dispersants
  • Offshore subsea dispersants
  • In-situ controlled burning
  • At-sea containment and recovery
  • Protection of sensitive resource
  • Shoreline and inland assessment
  • Shoreline clean-up
  • Inland response
  • Oiled wildlife response
  • Waste management
  • Stakeholder engagement and communication
  • Economic assessment and compensation
  • Environmental impact and assessment (including sampling)
  • Source control

Once completed, the model provides a visual depiction of the response capabilities available, as well as aiding responders with determining how to leverage those capabilities to mitigate the risk under each category. For further detail on using the evolving model, it’s recommended that you refer to the IPIECA Tiered Preparedness and Response document.

Incident Typing

In the United States, NIMS, ICS, and the National Response Framework utilized by regulators and emergency response agencies describes emergency incident complexity on a spectrum of Type 5 to Type 1 with Type 1 being the most complex. Incident typing also aids emergency managers in organizing a “right-sized” response by matching resources and capabilities to the complexity of the incident (i.e., Type 1 IMT for a Type 1 incident). Type 1-5 may also be used to describe scenario complexity for exercises.

  • Type 1 – Most complex, requiring national resources for safe and effective management and operation.  Type 1 response may continue for many weeks or months.
  • Type 2 – Incident extends beyond the capabilities for local control and is expected to go into multiple operational periods. Often requires the activation of response resources from outside the local area.
  • Type 3 – Incident needs exceed onsite capabilities and additional resources from the local area may be brought in to support the response. The response will last longer than one or two operational periods.
  • Type 4 – Minor incident that can usually be resolved within a day with onsite resources and support from other facility personnel.
  • Type 5 – Small incident that can usually be resolved within a few hours with onsite resources
    Tier/Type Overlap

    By overlapping Tier and Type descriptions, we can start to visualize how industry and U.S. Government responders are referring to similar incidents and events. By defining the level of response using standard terminology, incident responders are able to quickly understand the size, complexity, and response requirements of an event. To overgeneralize, Tiers and Types match up something like this:

It’s important to keep in mind that the dynamics of an incident or event make each one different. It is highly unlikely that you will be able to say that we had a spill at this location previously, so the new spill there should be responded to in the same manner. As the evolving IPIECA model demonstrates, there are lots of parts to consider in making your determinations on how to best respond to an incident.

So what does this all mean? In summary, responders need to be aware that there are at least two mechanisms for defining the complexities and size of a response. Having a basic understanding of how an organization may refer to an incident will better prepare you for knowing the level of effort needed to assist, as well as understanding the potential for the incident.

Since inception in 2000, EMSI has played a major role in helping government and industry clients alike, prepare, train, and respond to emergencies of any cause or size.  Comprised of national and international all-risk, all-hazard response experts, EMSI’s seasoned cadre gives us a unique background and perspective in dealing with incident and responder needs at every level of government and industry, to include the international community. As a global response leader in all-risk, all-hazard, multi-discipline incidents, EMSI has a proven track record in helping the myriad of local, state, national, international, and private sector entities with their incident management and emergency management programs.  EMSI is a service-disabled veteran owned (SDVOSB), minority business enterprise (MBE) that supports a broad range of clients. To learn more about EMSI and how we can help your organization’s response preparedness, please visit