The Use of Force Continuum.
Many law enforcement agencies use some form of a use of force continuum. This approach presents force in a ladder, or step fashion, escalating from one extreme to the other.
One of the obvious criticisms of the continuum approach is the suggestion that a security officer and in many cases private citizens must progress through the steps on the continuum before using deadly force. That approach may be appropriate if the suspect’s actions progress in accordance with the continuum.
However, in the case of a spontaneous and unprovoked edge weapon attack, there is absolutely no time to ponder the legal ramifications of the situation, without jeopardizing a successful defensive outcome. When a Security officer is on the job they should be aware of guidelines that will protect them from criminal prosecution or legal action.
Regardless of what force escalation options model is used, an potential victim should be confident in the following four areas before using any force whatsoever, but cannot be expected to consider these points when subjected to attack by a deadly weapon that could result in the immediate fatal wounding of the person by the attacker.
A commonly used continuum looks like this:

If the officer is involved in an incident that is in the process of escalating toward what could be a violent encounter, then they need consider the following:
1) Is my purpose for intervening fully legal? Am I acting on a lawful objective, a valid arrest, detention, search, or the defense of myself or a citizen?
2) Is my use of force proportional to the person’s resistance or could I use lesser force and still safely accomplish my lawful objective?
3) Am I confident and competent with all force tools I am legally authorized, to use or in the case of a private citizen, are the tools being used reasonable and appropriate for the situation.
4) Am I adding unnecessary elements to the situation by doing anything to precipitate the force?
5) Is my conduct out of line and not in the best interests of peaceful resolution to the problem?
6) Will a witness later testify that my language and or behavior contributed to or were instrumental in escalating the situation?
7) (In the case of Security) Did I carry out my duties in any way that could be considered unprofessional?
During the course of their job, an officer or private citizen may become involved in a situation which is already serious and immediate. The situation may then escalate, de-escalate, remain unchanged, or fluctuate quickly. Escalation of force only deals with one of these conditions. Understanding the quickly shifting nature of use of force scenarios is critical in developing the ability to respond within the legally acceptable parameters, whilst maintaining the necessary level of personal safety.
In today’s society these abilities have become a critical part of a security officer’s job requirements and private citizens must also be aware of the potential for legal retribution should they become involved in a situation where they unwittingly act outside the legally acceptable requirements.
Not Too Early, Not Too Late.
Officers must be trained to enter rapidly changing situations and do their utmost to use the appropriate type and amount of force in a timely manner, that is, not too early or too late, without directly contributing to any worsening of the situation. The appropriate amount of force response by the officer is largely dependent on the attitude, behavior and actions of the assailant.
The Internets Best Kept Secret.
A Question of Anatomy.