Rigging is the language of physics, the understanding that angles create leverage = “Hidden forces” and what might cause rigging failure. The judgement and comprehension of every force present in all rigging situation is beyond the extent of this article, but training and experience leads to effective safe work practices. A knowledge of understanding unforeseen forces with rigging will go a long way towards preventing an accident and accomplishing the task safely and efficiently.
Force can be defined several ways. Simple definition is push or pull. Force is more accurately defined by Newton’s Second Law of Motion. It states that “The acceleration of an object is proportional to the net force acting on it, and is inversely proportional to the objects mass”. Placed into equation, Force = Mass x Acceleration (F=ma). Forces can be either tensile or compressive, particularly when dealing with rigid bodies that we work with every day.
How do unforeseen forces play a part of rigging failures? The tower industry has documented deaths that were preventable had there been a better understanding of the “Hidden Forces”. Factoring for rigging components, angles, potential shock loads should be part of the pre-planning to minimize risk for an acceptable margin of safety. For example, when calculating forces, every known force should be included to allow for worst case shock loading of equipment and anchors being used. These predictable forces are tension, compression, shear, friction and gravity that can be calculated under static conditions.
Mechanics is the branch of physics concerned with the state of rest of motion of bodies’ subject to the action of forces. There are two main branches of Mechanics: Statics and Dynamics. Statics deals with the objects at equilibrium, which means at rest or moving at a constant velocity. Dynamics deals with accelerated motion.
As a result of static and dynamic forces, limiting the direction in which materials are loaded and the type has become increasingly more important. A main structural beam capable of holding or withstanding 15 tons of force horizontally, may break or become damaged under a load of only a few tons when applied vertically. Loading a structural element in a direction other than which it was engineered for is called side loading and there is a possibility to permanently and irreversibly damage a building or structure.
While it is comparatively easy to test the breaking strength of ropes, slings, and blocks (either working load limits or breaking strengths are printed on such equipment). The issue is the difficulty in the engineering equations for rigging, because simplifying assumptions upon which equations are derived are often violated.
Analysis regarding lifting and hoisting operations within the E&P sector, indicates that as many as 80 percent of incidents are related to human errors. These can, for example, be incomplete organizing of the operation, incorrect operation with regards to equipment and procedures, incorrect or incomplete maintenance or incomplete securing of the area where the lifting operation takes place.
A management/training program focusing to improve employees’ working environment, behavior and attitude can have a significant impact on the safety result in lifting operations, and, subsequently on the operational costs.
The most significant human factors in lifting and hoisting operations are found in the:
- Safety Culture/Working Environment
- Employee Training
- Facilities/Equipment
Characteristics of a good safety culture for lifting are:
- Respect for workmates, standards and rules;
- Compliance with legislation, standards and procedures;
- Commitment to encourage good practice and behavior and doing the right thing instinctively;
- Intolerance of inferior practice and willingness to intervene to ensure safety
In conclusion, a competent rigger on site should have a lift plan and if the lift deviates from the plan, make safe and STOP the job. Hazard identification and risk assessment are an integral part of planning a lift and an assessment of the lift and determination of the lift method. Equipment and number of people required are critical to planning of the lift and always be aware of the physics involved with the unforeseen forces of a lift.
By Kathy Gill, Owner at Tower Safety and Instruction
December 8, 2016
Reader Interactions