Answer to Question 1
PtD causes designers to think through what workers will actually have to do in constructing the permanent features of a structure. If any aspect of the design creates a hazardous condition the design is altered to eliminate or mitigate the condition.
Answer to Question 2
Heinrich's theory has two central points: 1) Injuries are caused by the action of preceding factors; and 2) removal of the central factor (unsafe act/hazardous condition) negates the action of the preceding factors and, in so doing, prevents accidents and injuries.
An illustration of the structure of the Sun:
Structure of the Early Universe
The Structure of the Atmosphere
A child in an orphanage in Juba, Sudan. The treatment of this child is likely to affect his ability ...
The material safety data sheet (MSDS) for sulfuric acid showing the detailed technical information ...
Structure and function of the gills of a bony fish.