HEALTH & SAFETY of PUBLIC & INDUSTRY

 Safety Factor In applying Equation 10-1, a safety factor or factor of safety is often introduced. A factor of safety makes an allowance for many unknowns related to materials, assembly, or use. Unknowns may be inaccurate estimates of real loads or differences between actual materials and those tested in laboratories. They may be changes in area resulting from corrosion, wear, manufacturing, assembly, or use. They may be irregularities or nonhomogeneity in materials. The unknowns may include suddenly applied, dynamic loads. Technically, a safety factor (SF) refers to the ratio of a failure-producing load to the maximum safe stress a material may carry. The maximum safe stress is often called the allowable stress. Failure may not be by rupture or fracture. A failure could be a change in area or properties of the material that affect the load-carrying capacity and its safety. For structural steel, the allowable stress is derived at the yield point in a stress-strain (load per unit ar...

Forces, Distribution, and Materials MECHANICS AND STRUCTURES  The magnitude of a force acting on a body is obviously important. As a rule, large forces are more likely to cause failure or damage than small ones. How a force acts on a body is also important. The direction of a force, its location or point of application, and the area over which it acts are also important in safety. A 50-lb force applied to the edge of a sheet of glass and parallel to it may not break it. If a hammer strikes the center of the sheet with the same force, the glass will probably break. A wood panel of the same size undergoing the same force will not break. When evaluating the strength of a material, it is essential to evaluate the distribution or concentration of forces as they act on bodies. Figure 10-1 gives some examples of distributed and concentrated loads. Experience tells us that different materials have different strength properties. Striking a glass panel will cause it to shatter, whereas strik...

                                              MECHANICS AND STRUCTURES April 27, 1978: In West Virginia, 51 construction workers fell 170 feet to their deaths as the scaffold and form work system peeled from the top of a cooling tower under construction. The lack of some required bolts connecting the scaffold to the tower and inadequately cured, insufficient strength concrete contributed to the accident. May 30, 1979: A DC-10 crashed in Chicago, killing 271 people. A 3 /8-inch diameter bolt supporting the engine pylon failed, causing the engine to break away from the wing. As it broke away, it ripped through three redundant hydraulic flight control lines. May 12, 1982: A report to Congress stated that more than 212,000 of the nation’s 525,600 highway bridges (40.5%) were structurally deficient or functionally obsolete. A structurally deficient bridge is one that has a reduc...

                                                                                  END                                                                               Key Tags Behavior Based Safety Safety Professional’s View Objectives Today: • Identify differences between traditional vs BBS • Know “when and when not” to implement BBS • Explain why most traditional safety programs don’t work! • Understand why positive reinforcement is much more powerful than negative reinforcement Why Safety Programs Do Not Work: • Safety is a priority, not a value! • Safety is not managed in the same manner as p...