LEEA foundation part-5.pdf - Safe Working Load(SWL The maximum load or mass(as certified by a competent person that an item of lifting equipment may

LEEA foundation part-5.pdf - Safe Working Load(SWL The...

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©LEEA Academy Foundation Step Notes Jan 2017 v1.5 59 Safe Working Load (SWL) The maximum load or mass (as certified by a competent person) that an item of lifting equipment may raise, lower or suspend under particular service conditions. It is the SWL which is required to be marked on the item by LOLER and which appears on any report of thorough examination. The Minimum Breaking (or failure) Load (MBL) The minimum breaking load is the calculated load at which a sample of the item will break or fail. From this value is derived the WLL etc. In order to ensure that this value has been achieved for some products, e.g. wire rope, a sample may be tested to destruction and the actual breaking load recorded, or the wire from which the rope is made is tested and the aggregate breaking load is calculated. Other items are designed so as to sustain the WLL plus a minimum factor of safety, e.g. a roundsling, however they may fail if this is increased by only a tiny amount. For practical purposes we can consider these tests to be the same. For a new product a sample must not fail under test at a lesser amount than the minimum specified in the relevant standard. The MBL should be expressed in the SI unit of force (Newtons) or Mass (tonnes, kilograms), as required by the relevant standard. Factor of Safety (FOS), Coefficient of Utilisation, Working Coefficient These terms all have much the same meaning, but perhaps Factor of Safety describes the function better than the more recent terms, which are replacing it in standards and legislation. It is a factor which is applied to the MBL to determine the WLL. It varies with the product to take account of the susceptibility to damage and considers the type of stresses the item will meet in normal use. Where the conditions of use are more severe than those considered by the product standard, e.g. in a chemical environment, the user will apply an increased FOS, so reducing the value of the SWL from that of the WLL. SWL and WLL Some confusion exists as to the WLL and SWL. The WLL is determined by the designer/manufacturer and is based on the mechanical properties of the item. A competent person specifies the SWL, based on the use to which the item will be put and will be dependant on: Whether the load is dead or alive The consequences of failure, e.g. when carrying radioactive material the risk is high and a greater factor of safety is called for
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©LEEA Academy Foundation Step Notes Jan 2017 v1.5 60 How the load is applied, e.g. slowly or suddenly The degree of possible misjudgement of weights or angles The duty cycle and working environment Any other factors which affect the safe working life of the item or the safety of the lifting operation The marked SWL normally has the same value as the WLL, but it may be less. For instance, in mining and nuclear power stations the WLL is often significantly reduced to obtain the SWL, as there are particular
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