The following is in the form of 2 linked articles. I would hope that these could be combined with the addition of actual manual handling along the lines of that included in BTCV`s "Dry Stone Walling". Comments in yellow relate to this. I would hope BTCV would be happy to allow use of the material I wrote for them since it is Health and Safety and the fact that much/most of the information I used came from previous work (in the somewhat convoluted agreement I had with them I retain the copyright to such material). In addition a booklet would allow scope for developing the weight calculation tables.
Essentially it is wrong to think that the regulations actually prescriptively limit how much weight can be lifted. The regulations did not actually require that the bags of cement be reduced in size, rather they required an assessment of how bags of cement could be safely handled, whilst providing guidelines on weights for lifting and lowering. The reduction in size was a by-product of this assessment.
It does not seem that it is generally appreciated that the weights given within the guidelines are only guidelines, they are not limits. Essentially the legislation sets out requirements for risk assessment and general good practice. There is no such thing as a safe weight limit, and the idea of the guidelines is that working within them should reduce the chance of injury. Incidentally I noticed on a recent trip to Crete that bags of cement are still the old size.
As a basic premise the regulations require that manual handling be avoided wherever possible (for example use machines instead) fortunately this is qualified with the proviso `where it is reasonably practicable to do so`, walling is safe for the time being! Probably. For example employers are required to provide information on the weight of the load and mark the heavy side of each load with an offset centre of gravity.... wherever practicable. As of yet stones in fields do not count. It does however have implications on the need to appraise workers/trainees of the need to assess the centre of balance, how to deal with it when lifting etc.
"Getting to grips with manual handling: A short guide" (HSE, 2003-4) is a glossier, updated and expanded version of "Getting to grips with manual handling: A short guide for employers". Whilst the content of the new version is still essentially aimed at employers it is (as was its predecessor) a particularly useful guide to the regulations for both employers and the self-employed, and is even of use to the keen amateur. The truncation of the title was presumably to encourage a wider audience to read it. It is available from HSE
It explains (page 5) that basically employers should:
Avoid the need for hazardous manual handling, as far as is reasonably practicable
Assess the risk of injury from any hazardous manual handling that can`t be avoided
Reduce the risk of injury from hazardous manual handling as far as is reasonably practicable.
Whilst employees should:
Follow appropriate systems of work laid down for their safety
Make proper use of equipment provided for their safety
Co-operate with their employer on health and safety matters.
In fact the Health & Safety at Work Act 1974 essentially set out these points. This requires employers to provide "such information, instruction, training and supervision as is necessary to ensure so far as is reasonably practicable the health and safety at work of his employees". At the same time it is the duty of the employee to "take reasonable care of the health and safety of himself, and other persons who may be affected by his acts or omissions", whilst co-operating "with the employer to enable him to comply with his health and safety duties. In many ways the Manual Handling regulations merely point in the direction of how we might dot the "i`s" and cross the "t`s" in a specific area of work practice.
So where does that leave us? Essentially you should assess the risks and work in a way that minimises them.
To help in this it sets out the points which should be considered (questions asked) when making a risk assessment for lifting (pp.9 & 10)
Does the work involve:
Holding loads away from the trunk; twisting, stooping or reaching upwards; large vertical movement; long carrying distances; strenuous pushing or pulling; repetitive handling; insufficient rest or recovery time; a work rate imposed by a process.
Are the loads:
Heavy, bulky or unwieldy; difficult to grasp; unstable or unpredictable; intrinsically harmful eg sharp or hot.
In the working environment are there:
Constraints on posture; poor floors; variations in levels; hot/cold/humid conditions; strong air movements; poor lighting conditions; restrictions on movement or posture from clothes or personal protective equipment.
It should be fairly obvious that most of these are particularly relevant when applied to dry stone walling it is after all essentially a process that involves lifting and handling in often far from ideal conditions.
The leaflet also includes information on lifting techniques and pushing/pulling which are beyond the scope of this article. But then you could always get a copy for yourself, if you`re that interested!
As to the actual guideline figures these are reproduced here:
For a pair of people lifting a single stone the figures increase by around a third (eg 2 males, load close to body, 33kg).
Interpreting these figures is not entirely straightforward. It should be fairly obvious to all that the amount you can lift is reduced if you are holding something at arms length, or if you try to lift it above your head.
Even more obscure is the implication that whilst it is applicable to carry a 25kg bag of cement at waist level it is not necessarily appropriate to lift it from the ground as this involves it passing through 10kg and 20 kg zones. For example to be entirely safe (as far as HSE are concerned) a bag of cement should ideally be carried from a stack at waist height and then placed on a platform/vehicle at waist height). Whatever you do, do not lean forward to pick up a bag of shopping! Come to think of it I`m dreading the day some jobsworth at the local supermarket realises the implications of these figures!
At the same time these figures "assume the handler is well trained, using the correct procedures and working in reasonable conditions with a stable body position, or in other words on stable ground. They also assume that the load distribution is stable, which requires good hand holds on regular shaped stones." ("Dry Stone Walling", Brooks Adcock Agate, BTCV, 1999). Just to complicate matters further it is recognised that factors such as better fitness, greater experience and appropriate training increase the amount a person can reasonably exceed the guidelines by. Realistically there is no actual quantitative limit to any of the zones although the HSE state that "any operations which would exceed the guideline figures by more than a factor of about two should come under very close scrutiny" (HSE, 1992, p43).
Contrary to popular belief there are not any actual limits on what you are permitted to lift. Provided you have assessed the risk sensibly, are aware of potential problems, work in a way that minimises the risks as far is reasonably practicable, and do not try to exceed your own capabilities (whatever they may be).
So we can just throw the guidelines away and get on with our lives, can we? Oh if it were only quite that simple. The mere fact that guidelines exist has implications, especially for employers (don't forget if you are a self-employed sole trader the HSE can prosecute you as an employer, since you employ yourself) and trainers. Whilst the figures in the guidelines are not compulsory, the fact that they exist means that if they are exceeded and injury results you would have to show that:
You had properly assessed the risk;
That there was a very good reason why it was reasonable to exceed the guideline;
That it was the only practicable course of action that could have been taken.
In the case of training you would also need to show that those involved had been appraised of the (foreseeable) risk and how to minimise it.
This naturally leads to the actual process of manual handling. Unfortunately that is beyond the scope of these articles. I`d like to think I covered it in good detail in "Dry Stone Walling" (pp22-25) which was adapted from my training handouts. [[As a booklet this technical process could be included, more or less as written in BTCV shouldn`t be a copyright problem as the information essentially comes from stuff I`d pre-published which was protected in the contract for the book]]
If you don`t have a copy it can be found online at http://handbooks.btcv.org.uk/handbooks/index/book/61
Failing that contact me and if you're lucky I`ll be able to dig out copies of my old handouts.
To sum up it is probably best to quote directly from the concluding paragraphs of the most recent "Getting to grips…"
"The risk assessment guidelines are not `safe limits` for lifting. But work outside the guidelines is likely to increase the risk of injury, so you should examine it closely for possible improvements. You should remember that you must make the work less demanding if it is reasonably practicable to do so. Your main duty is to avoid lifting operations that involve a risk of injury. Where it is not practicable to do this you should assess each lifting operation and reduce the ris of injury to the lowest level reasonably practicable. As the risk of injury goes up you must look at the operation increasingly closely to make sure it has been properly assessed and the risk of injury has been reduced." HSE 2003-04
If you've grasped all of this you're doing well. However have you any idea how much a stone weighs? This will be covered in a subsequent article, and if you thought the regulations were complicated, just you wait….. [[Add something on Combined handling if including technique. Can introduce additional hazards and doesn`t increase capacity by as much as you think. Both should have good space and ground conditions, you need to have sufficient handholds, one person takes charge (1,2,3 lift ... lift on 3, whatever, make sure know, ensure co-ordinated.) be aware many people will worry more that partner will drop it on them which has implications on the effort they put in...might also want to add something on mechanical aids reducing hazard from lifting but introducing other hazards which also sort of covers combined handling]]
Different stone types vary in weight for a given volume, according to their mass density. Scary stuff? Put simply a bag of sugar weighs a certain amount, the exact same size bag of foam pieces weighs less, a lump of solid lead of the exact same size will be heavier, because they have different mass densities.
This same principle applies to different types of stone. At one end of the scale oolitic limestone (Cotswolds) weighs around 2 tonnes per cubic metre, that is a solid block 1m x 1m x 1m weighs two tonnes). At the other end basalt, (e.g. Isle of Skye) weighs almost 3 tonnes per cubic metre - that is half as much again. This of course means that any given size of basalt stone will weigh half as much again as the same size of stone composed of oolitic limestone. This is quite a considerable difference.
A while ago I was building a new wall in a garden and needed some blocky limestone coping. I started off by calculating the total volume of coping (i.e. length of wall x top width x height of coping) and multiplied it by the MD. Not convinced by my answer, I calculated how many stones I would need (length divided by thickness of stone) then divided the total weight by the number of stones. The answer seemed ridiculously large. I calculated the volume of a single stone and multiplied it by the MD, same answer. I took a sample stone of about the same dimensions (300 x 400 x 150 mm) home and put it on the bathroom scales (my better half was out)! The result was very similar to my calculations, you should have a quick guess at what it was…. The answer is a somewhat scary 40kg (MD of 2.5 and the stone measurements were only nominal, by calculation the exact weight would be 45kg). Is it any wonder I have a bad back and problematic shoulders. Personally I do not regard that as a particularly large stone, pretty much an everyday occurrence around here (North Wales).
The moral of this story is that stone weighs a lot more than we think. This has serious implications for health and safety. Whilst the HSE guidelines are just that, guidelines, they have to be interpreted and you cannot do that if you do not actually have any idea how much a specific stone weighs. If you are training complete novices you could find yourself in serious trouble if someone injured himself or herself, and you could not demonstrate that you had highlighted the risks accurately. If you cannot show that you at least have some idea of how much a stone weighs, how can you have highlighted the risks accurately?
For those with a mathematical bent just multiply volume by MD. That is length x width x height (in cm) and multiply by MD (dividing by 1000 to convert to kg).
For everyone else I have tried to compile some sort of table that shows how big a stone would be given different mass densities, to meet the various guideline figures within the manual handling regulations.
I've assumed two dimensions for a stone, one side of 25cm and another side of 35cm. This is arbitrary but seemed a sensible start for a reasonably large stone (whatever that might mean, perhaps "not small stone" might be better).
Then as the weight will vary for whatever the bulk density of the type of stone is I have calculated the length of the other side for a wide variety of these.
Guideline Weight in kg bold figures to left
Bulk density in tonnes per cubic metre bold figures across top.
2.0     2.1     2.2     2.3     2.4     2.5     2.6     2.7     2.8     2.9
7       4.0     3.5
3.0     3.0     3.0     2.5     2.5
10     5.5     5.0     5.0     4.5     4.5     4.5     4.0     4.0     4.0     3.5
13     7.0     7.0     6.5     6.0     6.0     5.5     5.5     5.5     5.0     5.0
15     8.5     8.0     7.5     7.0     7.0     6.5     6.5     6.0     6.0     5.5
20     11.0   10.5   10.0     9.5     9.5     9.0     8.5     8.0     8.0     7.5
25     14.0   13.5   12.5   12.0   11.5   11.0   10.5   10.5   10.0     9.5
Figures rounded down to nearest 0.5 cm
Figures represent length of third side in cm of a stone where the other two sides are 25 cm and 35cm
Mathematically these figures are calculated by (1000 x kg)/(25x35xMD)
They are rounded down to the nearest 0.5cm since as in reality stone size is not going to be measured to the nearest millimetre. Rounding down also seems sensible as it provides a margin for error, rounding up and the stones would be too heavy.
For example a coping stone 25cm tall and 35cm long composed of oolitic limestone (MD 2.0) would need to be 11cm thick to exceed the guidelines for lifting to shoulder height, if it was slate (MD 2.7) it would only need to be 8cm thick.
In the previous article I mentioned that there was an "implication that whilst it is applicable to carry a 25kg bag of cement at waist level it is not necessarily appropriate to lift it from the ground as this involves it passing through 10kg and 20 kg zones". So theoretically all other things being equal it is not recommended that stones heavier than 10Kg are lifted from the ground (7kg for women). Whilst technically we can roll footings, use planks, or ramps for the lower courses it can be seen from the table that really it doesn`t matter what wall we a re building you cannot stick strictly to the figures. That is unless we all moved to the Cotswolds. Then of course we`d have bad backs from spending most of our days bent double, or through the repetitive strain of bending to build walls where no stone is more than 5cm thick and even metre high walls frequently have more than 20 courses. Sometimes I think the only true safe manual handling is to retire and get someone else to do it!
The figures below relate to coping in the event that you need to lift one above shoulder height, i.e. if it's a tall wall or short waller. As I`m dealing specifically with coping stone, rather than large stone in general I've assumed that the two known dimensions of the coping stone are 25cm and 30cm as these would cover most types. The resultant figure would then represent the thickness of the coping stone. I've calculated the figures to the nearest millimetre (rounded down) as they get a bit `samey` if you just round down to the nearest 0.5 cm.
They are quite frightening especially with regard to the female guidelines (7Kg). It should also be noted that you are more likely to stretch with coping. This would reduce the figures, although as you are only likely to stretch one arm rather than both, it doesn't exactly fit the guidelines. Make of it what you will, however be aware that it doesn`t take much for coping to exceed the guidelines, and however you look at it handling coping is potentially a particularly hazardous operation.
Guideline Weight in kg bold figures to left
Bulk density in tonnes per cubic metre bold figures across top.
2.0     2.1     2.2     2.3     2.4     2.5     2.6     2.7     2.8     2.9
7       4.6     4.4     4.2     4.0     3.8     3.7     3.5     3.4     3.3     3.2
10     6.6     6.3     6.0     5.8     5.5     5.3     5.1     4.9     4.7     4.5
Figures rounded down to nearest mm.
Figures represent thickness of a coping stone in cm where the other two dimensions are 25 cm and 30 cm.
I hope these figures/tables have served as an introduction to the idea of assessing stone weight. I`ve tried to keep it as simple as possible. I`m afraid if you want tables for specific stone types and dimensions you`ll have to calculate them yourself (although personally I think there ought to be a booklet available for trainers). However to be of some assistance here is a basic guide to the mass densities of various types of stone.
carboniferous limestone 2.5
old red sandstone 2.35
coal measures sandstone 2.3
new red sandstone 2.25
oolitic limestone 2.00 (2.15 if "Portland")
Unfortunately these are only guidelines and all can generally be expected to vary by +/- 5% (In some instances as much as 10%).