Build Stadiums and Theaters with Inferred Stairs

What are Inferred Stairs?

Sometimes Pathfinder models include stair access for occupants which are modeled without any of the user-defined stairs tools. In Pathfinder 2021.4 this modeling technique is automatically detected and occupants traversing the stairs now move according to stair behavior appropriate for the determined riser and tread distances. With the inferred stairs feature, Pathfinder users now have more flexibility in creating complex stairs without sacrificing in movement accuracy.

Stadium model showing stair connections to rows and aisles.
In this stadium model, the stairs need to connect with adjacent aisles. Landing steps with longer treads are designed to provide exit entry/exit access.

Why aren't stairs always explicitly created with the user-defined stairs tools?

When stairs are merged with surrounding areas to form aisles or to connect with uneven geometry, the user-defined stairs tools cannot provide the necessary connection points. This is common in theaters and stadiums where the aisles of seating rows connect to the stairs. The inferred stairs can be entered or exited from the sides to the aisles. Additionally, user-defined stairs cannot represent spiral stairs.

How are inferred stairs detected?

The inferred stairs feature is enabled by default. Disabling inferred stairs is described in the User Manual. Pathfinder will automatically detect sloped open areas which are not explicitly defined as stairs and determine the movement direction of the occupant. If risers are also identified, Pathfinder will determine tread length and apply the inferred stairs movement model. For more information, read the Technical Reference Manual.

Inferred stairs allow for accurate movement on stairs that were converted to rooms.
With inferred stairs enabled, occupants will have similar movement properties as if the user-defined stair tool were used. This advanced detection ensures that the model accurately portrays all stair movement.

What other changes were made to stairs?

Models using implicit stairs prior to the inferred stairs feature were prone to over-predicting distance and under-predicting evacuation time. With inferred stairs, those navigation features are detected and Pathfinder adjusts occupants' travel distance and velocity to better represent stair movement based on the design of the stairs. This will affect results of models designed in older versions of Pathfinder which are now run in 2021.4 with inferred stairs enabled.

How do occupants move differently on stairs?

Pathfinder uses the maximum speed defined in Profiles to adjust the actual speed while traversing stairs. It is possible to make detailed adjustments to stair speeds in the Advanced Speed Properties. The User Manual further details where the default settings are derived from and how adjustments will affect the results.