Lifting equipment training, plant audits, registers and codes of practice.
P O Box 3757, CRAMERVIEW, 2060 RSA Tel / Fax: +27 11 462 9620/1 Cell +27 82 372 4595
Website: www.phakamisasafety.co.za Email: potto@icon.co.za
Working Load limit versus Safe Working Load (WLL vs. SWL)
The lifting equipment terms, WLL and SWL of a product are confusing and
interpreted differently by Users, OEMs, the DOL and DMR inspectors etc.
This is exacerbated by different terminology used internationally, and as specified in
the RSA in different lifting equipment Regulations. It could also differ in written
company or mines Standard Operating Procedures. (SOPs or COPs)
The OHSA, DMR 18 (1) (b) lifting machines, and DMR 18 (10) (b) lifting tackle,
specifies that these items should be marked with the maximum mass load (MML)
The MHSA Chapter 8.5 (3) (c) specifies that lifting equipment (lifting machines) and
lifting tackle be marked with the SWL.
The lifting equipment Regulations in these Acts do not mention the word WLL that is
marked on slings and hoists by the OEM.
There is a difference between the WLL supplied by the OEM, and the SWL.
In the writers opinion it is the following:
The WLL of a crane, sling or hoist is specified by the OEM as the maximum load
that the item is designed for to lift, lower or suspend a load in an undamaged
condition and under specific working conditions. The WLL is specified in the OEM
catalogue, on their wall chart or literature. The WLL is determined by taking into
account the design factor of safety (FOS) of the item.
RSA legislation specifies that all lifting machines must be designed and
manufactured in accordance with an accepted (OHSA) or appropriate (MHSA)
international design Standard, such as a SANS, DIN, EN, BS, JIS or ASME or
equivalent. Note it does not have to specifically be a SANS.
These standards specify that the OEM will mark the product with the WLL of the
product and not the SWL!!
Therefore, a chain block (SANS 1594) and a lever hoist (SANS 1636) for example
will be marked WLL on the body of the unit.
Similarly, a chain sling, wire rope sling or webbing sling will also be marked on its
serial tag or washer, with the WLL of the sling in accordance to the requirement of
the Standard to which the sling is manufactured.
The SWL of a crane, sling or hoist can be the same as the OEMs WLL, or a reduced
WLL depending on the method of use and environment in which the item is used.
This new calculated safe load is referred to as the SWL.
Directors: P H Otto, M P Otto Reg No 1999/080640/7 Vat No 4090206469
Lifting equipment training, plant audits, registers and codes of practice.
P O Box 3757, CRAMERVIEW, 2060 RSA Tel / Fax: +27 11 462 9620/1 Cell +27 82 372 4595
Website: www.phakamisasafety.co.za Email: potto@icon.co.za
The following examples can be used to explain the difference:
1. As the angle between the legs of a multi leg sling increases, the original WLL
of the sling is reduced. This new rating, used at the specified angle is the
SWL. See OEM charts for ratings which are entitled WLL
2. As chain temperature increases as a result of lifting hot loads, the WLL of the
chain is reduced and the safe load to be lifted is the SWL. The SWL of Alloy
grade 8 chain, if used at 400 chain temperature when lifting hot loads, is
25% less than the rated WLL supplied by the OEM.
3. As the boom of a mobile crane extends, or the lifting angle increases, the WLL
of the crane is reduced. The SWL is accordingly indicated on the load chart.
4. The number of sheaves used on a crane will determine the SWL of the crane.
It could be a 60 ton WLL crane with 6 falls of rope but if only 4 falls are used
the SWL of the crane is only say 40 tons.
5. The WLL of a chain sling, if used to lower persons such as used on mining
kibbles, is reduced as the SWL is calculated at a factor of 10:1, instead of 4:1
which is the normal design factor for alloy grade 8 chains.
6. Beams will normally be marked SWL as the safe load to be suspended from
the beam is calculated depending on design, dimensions and strength of
material used to manufacture the beam.
7. The SWL of a hoist will depend on how the hoist is used. If angular loading is
applied, the SWL is less than the marked WLL on the hoist.
8. A bow shackle is marked with the WLL which only applies if the shackle is
used in a straight line. The SWL at 45 is 30% less and at 90 is 50% less.
9. If for example, slinging abuse such as shock or impact loading, sharp
cornered loads, extreme temperatures or working above persons is
unavoidable, the WLL of equipment must be reduced to a SWL.
Therefore, management or responsible persons can specify on a construction site,
mine or plant that the OEMs WLL be reduced and the new safe load to be lifted,
depending on operational conditions, is then referred to as the SWL.
Users therefore cannot insist that slings or hoists be marked with the SWL,
as the relevant Standard to which the product was manufactured to,
specifies that the OEM must mark the product with the WLL.
Lastly, it is important to note that no matter whether the product is
marked, MML, SWL or WLL, the load stipulated must not be exceeded.
The above opinion is that of the writer only and without prejudice or bias un-
towards any party or person.
Piet Otto
March 24, 2015
potto@icon.co.za or mobile 082 372 4595
Directors: P H Otto, M P Otto Reg No 1999/080640/7 Vat No 4090206469
