Explosion Response Decision Tree

Fortunately, not all explosion scenes are equal to those that were encountered in Oklahoma City and at the World Trade Center in New York City. However, given the resources, smaller scenes, such as a fuel gas explosion that levels a residential structure or a small explosive device that kills a person, can be just as difficult for the small community. The following guide to responding to explosions is only provided to be a working model that hopefully will assist the first in company officer, wherever they may live. 

Normally, dispatch provides us with notification of an emergency and provides us with many of the essential items required to make initial response decisions. And, for this discussion, we will work forward from that point. It should be noted, however, that the amount of initial information may not be sufficient to get a clear and concise mental picture of what we will face upon arrival.

A. First Responder

1. Incident Size - Up

As with all emergencies size-up starts with the receipt of the call and continues throughout the emergency. Observations and reports of the sector officers are an important part of the success.  In that the intent of this particular section is to assist in the determination of the type of incident and not to teach Size - Up, all of the steps will not be included. If you are unfamiliar with the requirements of size - up, then additional research will be required. 

2. Immediate Emergency Responsibilities

a. Size of the scene/incident

As indicated, the size of the incident will dictate the level of response. As the first in company officer to a major incident, you will need to call for additional response immediately. 

b. Victims

Good Triage operations will be of assistance in patient treatment. Triage, as is already known, will provide the greatest care to those that we can impact. For those that we are not able to help, it is best that they be left where they are. In the event of an explosion, especially one that involves an explosive, there may be valuable evidence contained on the clothing or around the body. 

3. Suspects

While the primary role is not in the apprehension of suspects, the company officer should be observant of the crowd upon arrival. This would be especially true if an injured person is attempting to leave the scene without treatment. Leaving the scene and not seeking medical treatment is not grounds for declaring someone guilty, but it would be worth detaining the individual until help arrives. 

4. Safety

Safety will not be addressed in detail in this section. There is an additional section of this presentation that covers a listing of the safety issues. SAFETY 

5. Initial Incident Assessment

The initial incident assessment that is normally followed, is designed to assist the Company Officer in controlling the emergency. The model that follows is intended to assist the Company Officer in determining the type of incident that they may be faced with. Again, and I can not stress enough that the normal incident procedures be followed concerning the control of the incident. 



Determine the Incident Type

Based upon conditions observed upon arrival at the scene, the company officer can make some analysis of the type of incident that they are faced with. When completing the observation, care should be taken to look at both the gross effects as well as the subtle effects. 


a. Identify Explosion or Fire

Burning or Heat Treatment:

Burning and heat treatment could indicate that it is only a fire scene. 

However, consider the fuel gas explosion, that type of event may also have signs of burning present. 

So, in looking at what would be considered a normal fire scene we would have to look for any signs of overpressure.  


As there have been no indications of overpressure, it would be safe to classify this incident as a fire. This incident would continue based upon the conditions observed and normal departmental procedures. Priorities would be established to provide the appropriate care for injured, property preservation and protection, and also for the completion of any required investigation to determine the cause of the event. 

However, if during the initial scene assessment or if information is provided that the incident involves an explosion, then several additional considerations will be made. 



Are there any signs of overpressure?

Windows not intact.

Walls bowed or out. 

Condition of furnishings.

Condition of victims.

Debris in the yard.


Fire or Explosion?

b. Explosion Scene Priorities

Safety of Responders

Remove Injured

Leave Dead

Control Emergency

c. Explosion Scene Safety

Structural Integrity

Hazardous Chemicals

Bloodborne Pathogens

Fuel Leak

Secondary Devices, if an explosive is involved.


Type of Fuel?


Now that it has been decided that the incident is an explosion, the next step in the process is to determine the fuel that most likely was the cause of the event. 


To do this, we would need to quickly examine the scene to determine if the explosion was seated or non-seated. 

Seated: Condensed Phase Fuels

As indicated in the Explosion Theory section, a seated explosion is one that has a definite center or crater. Again, the use of the term "crater" does not necessarily mean that there is a hole in the ground. It is used to designate that area that the event started. With seated explosions, the more fuel present the larger the crater or hole. 


Liquid Fuels

Mechanical Explosions


Starting from the top left hand corner: 

The scene shown is a seated explosion. Careful examination of the table in the photograph indicates an area of greater damage. Given a residential occupancy and the lack of signs of a mechanical explosion (BLEVE) it would be reasonable to consider a scene where an explosive was the primary fuel. At this scene care must be taken to determine that the scene is safe, especially as a result of a secondary device. Assistance should be obtained from a Bomb Technician to check the scene in addition to the other safety concerns. 


The scene shown in the top right photograph, also indicates a seated explosion. But, this time, an explosive material was not utilized. As the scene can be identified as a railway incident and it involved a BLEVE of a railcar. 


The scene shown in the lower left of the series, also indicates a seated explosion. Now, given this scene, what do you think is the most likely fuel involved. Looking closely at the car and considering fuel types, it would most likely be an explosive material. 


The scene shown in the lower right of the series, is difficult to call. Based on the information provided, there is a center shown, but that is the building itself. 



As a response priority and issue, if there is a belief that a seated explosion is as a result of the initiation of explosive materials, then consideration must be given to the notification of a responding Bomb Squad and also to the appropriate Federal Agencies. Additional care must also be given to the scene and evidence preservation. 


If the explosion is as a result of a BLEVE, than there are a number of other issues that will have to be taken care of. Issues dealing with the type of fuel that was in the tank, additional tanks that could also be ready to BLEVE or have been damaged as a result of the original incident, structural conditions, and others. 


Non-Seated: Diffuse Fuels

As indicated in the Explosion Theory section, a non-seated explosion is one that does not have a definite center or crater. There may not be an area of greatest damage, only a direction of force indication on materials. 



Fuel Gases

Dusts and Fines


The scenes shown are all non-seated explosions and were a result of a natural gas leak and subsequent fuel gas explosion. In each of the scenes selected, there was extensive damage and with that much damage if it was a seated explosion the seat should be very evident.


In each of these events, the first responding company officer has to consider additional explosions, especially if the fuel is still leaking. Prior to entry into the area, shut off the source of fuel.



Conclusion and Summary

The intent of this section was to assist the company officer in understanding the importance of first recognizing an explosion incident and then to look at some basic procedures that can be used to determine the type of fuel that most likely was involved. After the basic fuel is identified, it will be easier for the company officer to work towards a safer conclusion of the incident.



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Copyrightę1999 All Rights Reserved

Ron Hopkins

TRACE Fire Protection and Safety Consultants, Ltd.

123 Redwood Drive

Richmond, KY 40475