The first phase of immersion is engagement.

To archive the first stage of immersion, the user must accept an investment of time and the experience must match the user's preferences and offer an entry level of control that is accaptable.

Barrier 1. Accessibility
Experiencer preference is met e.g. if the content is about sport and the user doesn't like sport they are unlikely to engage with the content. Controls and expertise level are intuitive and easy to learn.

Barrier 2. Time
Willingness to invest time. If the experiencer is unwilling to invest time in the experience then they are unlikely to become engaged.
Availability of time. The experiencer must have time available to partake in the experience.

The second phase of immersion is engrossment.

To achieve the second stage of immersion, the user must accept their surroundings (environment) and successfully ignore/remove external distractions.

Barrier 3. Depth of World
The world looks visually believable.
The experiencer is set believable tasks.
The plot / narrative is believable.

Barrier 4. Distractions
Removal of all exterior distractions.

The third phase of immersion is total immersion.

To archieve the final stage of immersion the user must achieve a psychological sense of being in a virtual environment (presence) and state of "flow" where by they are so involved in the activity that nothing else seems to matter.

Barrier 5. Empathy
The growth of attachment / addiction.
The embodiment of a character.

Barrier 6. Awareness
A lack of awareness of time (flow).
A loss of awareness of the real world (presence).

This is classification by Emily Brown and Paul Cairns. Nobody knows when we will able to develop total immersion application. Now we can play in the fist and the second steps.