The strategy of individuals in evacuating buildings was investigated by John Abrahams in 1994. The independent variables were the complexity of the building and the movement ability of the individuals. With increasing complexity and decreasing motion ability, the strategy changes from "fast egress", through "slow egress" and "move to safe place inside building" (such as a staircase), to "stay in place and wait for help". The third strategy is the notion of using a designated "safe haven" on the floor. This is a section of the building that is reinforced to protect against specific hazards, such as fire, smoke or structural collapse. Some hazards may have safe havens on each floor, while a hazard such as a tornado, may have a single safe haven or safe room. Typically persons with limited mobility are requested to report to a safe haven for rescue by first responders. In most buildings, the safe haven will be in the stairwell.