For the seat belt to be effective, it is essential that it is **properly fastened to the body**. This helps to prevent the **submarine effect**, which occurs when the body slides down and under the belt during an accident. This sliding can happen if the belt is improperly positioned or if the seat is reclined too far back.

- **Shoulder strap**: It should pass over the collarbone, between the shoulder and the neck, and go down the center of the chest. If placed incorrectly, it can cause serious injuries or reduce protection in the event of an accident.


- **Lap belt**: It should be over the hip bones, always below the stomach. Placing it over the abdomen can cause serious internal injuries in the event of an accident.


A well-adjusted seat belt not only prevents the submarine effect but also increases the chances of surviving an accident, as it keeps people in their seats and prevents them from being ejected from the vehicle. Therefore, it is crucial to ensure that the belt is properly fastened and correctly positioned.