Obstruction – any object that makes it impossible for people to occupy or move through a certain area of space.
The most obvious obstructions are any physical objects: walls, solid objects, stairways, floor slabs and landings. Clearly, a person cannot move or even remain at a point in space occupied by a physical object.
On the navigation graph, obstructions are displayed as red edges.
A small black segment located in the middle of an edge points toward the obstruction free side — the area where people’s movement is possible.
Minimum Height of Evacuation Routes
If an obstruction is located very low above the movement level (the distance from the movement level to the bottom edge of the obstruction is less than the Minimum Height parameter specified in the evacuation modeling settings), this area is also marked as prohibited for movement.
The figure below illustrates that the area beneath the platform and stairs is prohibited for movement because the distance from the floor level to the platform and stairs is less than the minimum allowable height.
If a stairway or ramp is above the minimum allowable height, only part of the space under the stairway will be marked as if an obstruction is present there. Clearly, there is no real obstruction in that space; however, the area near the lower edge of the stairway is blocked for movement:
Additionally, in real buildings, there must be unobstructed space above stairway to allow people to move up or down without hindrance. Therefore, a portion of the space above the stairway near their upper edge is also marked as prohibited for movement. Typically, such a “virtual” obstruction is added to the area formed by the floor:
Minimum Width of Evacuation Routes
A person cannot pass through very narrow sections of a path. The minimum width of a path that a person can pass through is defined by the Minimum Width property in the evacuation modeling settings. By default, the minimum width is set to 0.7 meters.
If it is necessary for a person to pass through a narrower opening, the value of the Minimum Width property in the evacuation modeling settings must be reduced accordingly.
The minimum value that can be set for the allowable width is 0.3 meters.
It is important to note that a person’s “contingent width” does not affect their ability to pass through paths narrower (even significantly narrower) than their own “width.” For example, even individuals in wheelchairs — whose typical width is around 0.8 meters — would be able to “squeeze through” a gap only 0.3 meters wide. Such unrealistic movements must be prevented.