To limit the probability that treads and risers will be designed with different dimensions [i.e. nonuniform run and rise dimensions], which could lead to difficulties in movement in an emergency situation, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons.
To limit the probability that treads and risers will be designed with different dimensions [i.e. nonuniform run and rise dimensions], which could lead to persons tripping or falling, which could lead to harm to persons.