The **submarine effect** occurs when, in an accident, the occupant's body slides downward, beneath the seat belt. This mainly happens due to **improper use of the seat belt or the vehicle seat**.

- **Improperly positioned seat belt**: If the seat belt is not properly adjusted to the body, it will not adequately restrain the occupant in the event of a collision.
- **Seat reclined too far back**: An incorrect posture, such as reclining the seat too far back, makes it easier for the body to slide under the belt.
- **Items on the seat**: Placing objects like towels or cushions on the seat can cause the occupant to slip more easily.

To avoid this effect, it is crucial to fasten the seat belt properly, ensure it is well adjusted, and maintain a proper posture while driving.