Active Shooters, Threat Assessment, and Prevention: How Threat Assessment Gets Us Left of Boom

The term ‘left of boom’ was used to describe efforts to prevent and protect military personnel from roadside bombs or IEDs (improvised explosive devices). The boom refers to the detonation of the IED. Left of boom refers to efforts to protect soldiers and prevent the detonation from occurring. ‘Left of boom’ refers to time, not geographic distance. The farther in time the intervention is from the detonation, the more ‘left of boom’ a prevention, detection, or protection effort is.

Active Shooter Threat Assessment - Left of Boom

For example, sensors which detect the presence of bombs in front of a vehicle while it is moving down a roadway are closer to a potential detonation than observation posts meant to observe the placement of IEDs. The observation post is more ‘left of boom’.

Any effort to protect our soldiers from IEDS is important and should be pursued. However, when I first heard it, I didn’t really like the term – left of boom.

But I find the thought process this term evokes useful when I think about other problems and, in particular, active shooters. Efforts to prevent and protect against active shooters also can be thought of and assessed according to how far ‘left of boom’ they are from an incident. For you, thinking about prevention this way might help when trying to identify methods to protect your community.

For the purposes of this post, we will rely on the common definition of US government agencies describing an active shooter incident as involving an individual “actively engaged in killing or attempting to kill people in a confined and populated area”. This would include incidents such as the Pulse Nightclub shooting or the 2017 shooting on the Las Vegas strip.

Types of Active Shooter Threat Assessment

Let’s take a moment and revisit the different challenges that active shooter threat assessment might be trying to solve. Threat assessment approaches and related challenges include:

  • Security Threat Risk Assessment: Plan for and protect facilities and critical infrastructure in communities against attacks.

  • Violence Threat Risk Assessment: Assess the likelihood of a specific individual for some form of violent behavior in the future.

  • Threat Assessment for Instrumental Violence: Identify, assess, and intervene with a person who may commit an attack (e.g. a shooting at a specific time and location).

  • Active Threat Assessment: Help law enforcement or security personnel to identify and react to threatening individuals (such as active shooters).

More detailed descriptions of each threat assessment approach can be found in our Guide to Threat Assessment Approaches for Law Enforcement. These threat assessment approaches, and the challenges they are trying too solve, are different. They apply at different times and in different ways to the prevention of an active shooter incident.

A Model of Active Shooter Threat Assessment Approaches

In an effort to understand how the different types of threat assessment are relevant to an active shooter incident I thought a visual aid might be helpful.  In Figure 1, I captured the different forms of threat assessment and their relevance to an active shooter incident. You will note that time is established based on the time-distance from an event (or how far left of boom).  I have also divided the threat assessment approaches based on whether they are environment and individual. The different lengths of the hash marks along the horizontal axis are purposeful; to convey the increasing time-distance from an incident.

Figure 1. Active Shooter Threat Assessment Approaches

Now, let’s think about the different forms of threat assessment and how left of boom each are from an active shooter incident.

Security Risk Threat Assessment is important farther left of boom. It is environmental and involves identifying and protecting a location from threats (such as active shooters). It could involve such recommendations as improving access control or establishing hardened locations to protect potential victims. While it can help prevent or mitigate damage, it is less relevant closer to an incident.

The individually-focused Violence Threat Risk Assessment is relevant far from and close to an incident. This approach involves assessing people who may commit some form of violence. It is not necessarily tied to the commission of a specific violent act. However, this Violence Threat Risk Assessment may be incorporated into the Instrumental Violence Threat Assessment if a threat assessment team has identified a specific subject in need of evaluation and intervention.

Because it involves the intersection of a location, a time, and an individual who might be planning an active shooter incident, the Instrumental Violence Threat Assessment is both environmentally and individually focused. It involves efforts to identify, assess, and intervene with individuals who may commit a specific violent act at a location. It is relevant to preventing an active shooter incident in the short and medium term.

Active Threat Assessment is also relevant nearer to an incident (i.e. just left of boom). This threat assessment approach involves a focus on the environment and individuals in it. This methodology could help identify individuals for referral to a threat assessment team or help to identify external threats to a location. Active Threat Assessment’s focus on identifying persons carrying weapons is also relevant to police response during an active shooter incident.

The police response to an active shooter incident involves additional tactical skills and considerations than the threat assessment approaches described here.

Thinking About Active Shooter Threat Assessment and Prevention

Each of the four threat assessment approaches outlined here are important to preventing an active shooter incident, but in different ways. Each may also be relevant to different communities and facilities at different times.

Active Shooter Threat Assessment - Prevention

Active Shooter Threat Assessment - Prevention

The nature of the location being protected will also impact prevention. Some locations are more secure (with controlled access) while in others people can move freely in and out of them. Secure locations can plan and protect against active shooters, but must also deal with the insider threat. In more open locations where people have freedom of movement, it is difficult to prepare visitors for an attack. Other locations have a mix of secure and open areas.  All are challenging to protect.

This post is exploratory. Over the last year or so I have sought to better understand threat assessment in all of its forms. I frankly found it a bit confusing and it has been helpful to learn how different forms of threat assessment apply in different situations. Drafting this post has also helped me to better understand threat assessment and how our own active threat assessment methods are relevant to an active shooter incident.

For you, perhaps thinking about how each of these threat assessment approaches and their time-distance from a incident (i.e. how far left of boom) will help you to identify gaps in your community’s efforts to prevent active shooter incidents and help you identify resources and training which can keep your officers and communities safe.

If you would like to learn more about active threat assessment or active threat assessment training, please don’t hesitate to contact us.


Atkinson, Rick. (2007). The IED problem is getting out of control. We've got to stop the bleeding. Washington Post. Available at

Nathan Meehan Ph.D.