The LEEA, in conjunction with HSEOSD, the author of the report, and representatives from other interested parties undertook to draft guidance. The end result was a LEEA publication called “Code of Practice for Selection, Management, Use, Maintenance and Examination of Hand Chain Blocks & Lever Hoists in the Offshore Environment including Sub-sea”.
Prominent amongst the interested parties was the International Marine Contractors Association (IMCA). Our code covers a wide variety of offshore applications both on deck and sub-sea. IMCA’s main focus was the use of chain lever hoists sub-sea and, in parallel with their input into our code, drafted its own code: IMCA D 028 dated June 2002.
With five years experience of using that guidance and investigating incidents which occurred during that period, the IMCA has recently published a revision dated February 2008.
As you might expect, with the common origins of both documents, the guidance from IMCA is very much in tune with that of the LEEA. However the fact that incidents have continued to occur indicates that there is still some way to go in getting the message across to everyone in the offshore industry. The guidance given in IMCA’s document is excellent and well presented but perhaps part of the reason it is not always followed is a lack of understanding of what is behind the guidance. This article therefore looks at what I consider to be some of the more important operational points, and attempts to explain the reasons behind them.
In their section on general principles the IMCA states that the equipment should be safe and suitable for its intended purpose. That may seem blindingly obvious but the majority of lever hoists used offshore are standard, series produced industrial products not specifically designed for use in a marine environment where they are exposed to the corrosive effects of salt water. Therein lies the cause of many of the problems. Some may be inherently more suitable than others. Some may be modified in some way for that purpose but all can be affected by corrosion and other contaminates. They are not inherently fully suitable for the intended purpose and must be managed accordingly.
Looking at operational issues, the IMCA document deals extensively with light load conditions and starts with the requirement that the lever hoist brake should function down to 5% of the WLL. Sadly the quality of some products on the market is such that, even straight out of the box, they will not achieve that. Initial selection and testing is vital.
Failure at light load is one of the more frequent causes of incidents. Corrosion and contaminates generally increase the minimum load required to satisfactorily operate the brake. It is therefore essential to make a light load test before first use, after any maintenance and routinely before issue from stores. As the light load test is done on a lever hoist in good condition, you can safely assume that in service, it will always require more. Good practice is never to work at less than 10% of WLL – but remember why. The worse the corrosion, the higher it will be and, if bad enough, the brake could seize and remain open at any load. Hence regular checking is essential.
There is a requirement that the chain stop which prevents the chain from running out should be capable of withstanding at least 2.5 times the maximum tension in the load chain at WLL. That may sound at lot but to understand why, think about what happens when the chain is run full out. The load cannot react against the lever so the brake is open. Effectively the load sheave is now just an idle wheel and the tension in the chain is transmitted to the last link and end stop. The operator has not realised that he or she has run out of chain so continues to pull on the lever. Most lever hoists need a considerable effort on the lever to open the brake for lowering. The operator could easily apply an effort equal to or even in excess of that required to raise the load before realising that something is wrong. The operator’s effort gets transmitted to the load wheel and thence to the chain. Now the end of the chain and the stop have the force arising from the lever added to that arising from the load. The total is already in excess of two times the maximum tension at WLL. If the stop fails, the chain runs through and that is the point of no return, the load drops.
A lack of understanding of this has been the cause of many incidents, not just in the offshore sector but throughout all industries. It applies equally to hand chain blocks where the slack end of the chain is usually anchored to the block frame rather than being secured by a stop.
Regrettably I do have one criticism of the IMCA guidance on this matter. Their illustration of a typical chain lever hoist shows a ring through the last link of chain as the end stop. This is almost certainly inadequate. The internal width of the chain link is only slightly larger than the diameter of material from which the link is made, just sufficient to ensure free articulation. The section of such a ring can therefore only be of the same diameter as the link material. It will not be of the same material or heat treatment or tensile strength. In practice most we see are only a piece of mild steel rod formed into a ring and sometimes not even welded closed. We also see rings which are little more than a key ring. If the chain is run out as described above, such rings will simply collapse and pass over the load sprocket allowing the load to drop.
Chain lever hoists along with other portable lifting equipment are often returned to onshore workshops for maintenance and examination. Whilst it may leave the workshop in serviceable condition, experience has shown that it doesn’t always arrive so. Protection in transit is essential. Again this may seem obvious, but one problem we identified was that equipment was sometimes delivered to the docks and ‘inspected’ at the quayside before being shipped offshore. The unpacking necessary for inspection was not re-done adequately with consequent deterioration of the equipment.
The revised guidance contains a new section dealing specifically with using chain lever hoists underwater. It advises against relying on a chain lever hoist to sustain a load for an extended period and instead recommends the use of static rigging or the fitting of an additional chain stop close to the body of the lever hoist. One practice which I recommend is whenever possible to finish any load movement by operating the lever hoist in the lifting direction if only by one click of the ratchet. The reason is that when lowering, it is the reaction from the load which closes the brake. As already mentioned a light load may not be adequate. However even a load nearer the WLL will only close the brake sufficient to hold the load. Changing direction and starting to lift ensures that the brake is fully closed.
The guidance also advises against using a chain lever hoist in a dynamic arrangement such as an adjustable leg in a slinging arrangement. This is because of the perceived risk of slippage, particularly if lowering through the splash zone where the weight could temporarily come off the brake mechanism. Although I would not disagree with their guidance, which errs on the safe side, such slippage is only possible if the brake is not fully closed at the time.
Using a chain lever hoist as an adjustable leg of a slinging arrangement to facilitate load orientation is a common and safe practice, particularly for installing or maintaining equipment which requires precise positioning. The tension on the lever hoist will drop to zero during landing but this will not affect a fully closed brake. The slippage which can occur with a light load is due to the brake not closing properly. When used in a dynamic arrangement with a power operated crane, an allowance must be made for the higher dynamic loading arising from the crane. Generally a 10% reduction in the WLL of the lever hoist is required, not forgetting also to allow for the angle at which it is loaded.
Another practice the guidance advises against is that of applying load to the lever hoist other than through the lever. If the load is to be transferred from another lifting machine it is far safer to use the lever hoist to take the load from the other lifting machine than for the other machine to give it to the lever hoist. This avoids any accidental shock loading of the lever hoist and also gives warning of any possible overload. This is because the effort required on the lever is in direct proportion to the weight of the load. The length of lever coupled with the gearing of a lever hoist is such that a considerable effort is required to lift an overload. The weight and strength of the individual operator and the position from which they are operating clearly influence their ability to apply the effort but an experienced operator will soon have a feel for the amount of effort required and will sense an overload.
The IMCA document contains much useful guidance on other aspects of using chain lever hoists sub-sea. As stated at the outset, this article only deals with some of the more important operational points and the reasons behind them. It is hoped that by understanding what lies behind the guidance, those responsible will be in a better position to implement it effectively.
More details on the International Marine Contractors Association (IMCA) can be found at www.imca-int.com
