Searchers should use a buddy system or two-in, two-out system and have backup teams available. Techniques for searching for potential victims are based on identifying possible locations of victims, or areas of entrapment. Areas of entrapment inside damaged structures are called voids. There are several types of voids, such as the pancake void (multiple floors of a building have collapsed diagonally onto each other), and the lean-to void (a single wall or floor has collapsed diagonally against another wall). Voids can also include spaces where victims may have entered for self-protection during a disaster - such as under desks or in bathtubs or closets.