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Fall arrest is a technique used to protect persons who work at Height . It is a form of "fall protection" and should be used only if "fall restraint/ prevention" techniques are not reasonably practicable. There is an established "hierarchy of fall protection" which determines the order in which different techniques should be considered. These are techniques and it should be noted that Equipment that is rated for "fall arrest" may be used for "fall restraint". Equipment that is rated for "fall restraint" only, should not be used for "fall arrest", due to a lack of Energy Absorption . Effective use of all "Fall Protection" techniques is dependent on having the correct equipment, competencies and controls. These are all management functions! For more info refer to ''BS8437:2005 Code of practice for selection, use and maintenance of personal fall protection systems and equipment for use in the workplace'' There is currently no other guide to this subject. The often quoted EN795 is only a guide for manufacturers of anchorage systems and provides little guidance on how to design or how to use such systems. COLLECTIVE AND PERSONAL SYSTEMS Fall Arrest systems can be either Collective or Personal. A Collective protection techniques protect all of the workers in the work area, where as Personal protection techniques protect each worker individually. Examples of different fall protection techniques include: ''Collective Fall Prevention'' - Physical barriers isolating workers from fall hazard - such barriers can be fastened to the structure or can be free-standing using counter-weights ''Collective Fall Arrest'' - Netting or matting which will stop the fall or a worker in a controlled manner - these are normally only suitable for tasks of limited duration, such as construction work ''Personal Fall Prevention'' - A combination of PPE (Personal Protective Equipment) and anchorages which limit the access of workers to areas where there is no fall hazard ''Personal Fall Arrest'' - A combination of PPE and anchorages which may not prevent a worker from reaching a fall hazard, but if a fall does occur, it will be arrested in a controlled manner PERSONAL FALL PROTECTION SYSTEMS These systems must include 3 elements referred to as ABC: A - Anchorage - a mechanical system fixed to the structure - such as a Horizontal Life Line B - Body Wear - a full body Harness worn by the worker C - Connector - a subsystem connect the anchorage to the harness - such as a Lanyard Without all of these elements, there is not a complete system and the Protection technique cannot be used. ENERGY ABSORPTION To arrest a fall in a controlled manner, it is essential that there is sufficient energy absorption Capacity in the system. Without this designed energy absorption, the fall can only be arrested by applying large Forces to the worker and to the anchorage, which can result in either or both being severely effected. An analogy for this energy absorption is to consider the difference in Dropping An Egg onto a stone floor or dropping it into soft mud. Even for the same fall Distance and Weight of egg (the input Energy ), there will be more Damage with the stone floor as the arrest distance is smaller and so forces must be higher to dissipate the energy. For the soft Mud , the arrest distance is longer and so arrest forces are lower but the egg is still stopped and is hopefully undamaged. Most fall arrest anchorages are designed on the basis that all workers will have a connector which includes an energy absorber. Hence, when using such systems, it is essential that the PPE used is rated for Fall Arrest and includes an energy absorber. A common form on anchorage device is an HLL (Horizontal Life Line). These are linear anchorage devices, which allow workers to move along the whole length of the anchor, usually without needing to disconnect and fixing points of the anchorage. It is normally essential to include energy (or shock) absorbers within HLL in addition to those within the workers' PPE. Without such absorbers, the horizontal life line cannot deform significantly when arresting the fall. This in turn results in large resolved forces being generated within the anchorage system, which can readily be sufficient to cause failure of the anchorage system. This can occur even with energy absorbers being included in the PPE of the worker. FALL CLEARANCE In arresting a fall in a controlled manner the distance required to arrest the fall must be considered. This is a Function of the "fall factor" and the deployment of the "energy absorbers". As a rule of thumb for a factor 2 fall, a fall distance of approx 6 Metres will be required. This is equivalent to 2 storeys of a Building . If the fall clearance is less than this the worker may strike the ground before his fall is arrested. DESIGN OF HLL SYSTEMS This is a complex process. The designer should always perform a design Calculation and the results of this calculation should be presented in any proposal and verified as acceptable. The loads applied to the structure and the fall clearance required should be checked. SEE ALSO EXTERNAL LINKS Overview and Images of Fall Arrest Systems and Components |
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