Why are there amber, red and purple zones as the total number of lifts increase?
When somebody lifts at low frequencies there are pauses between each lift. As the frequency of lifts increases, the demands on the heart and lungs increase because the person is spending more time moving. These boundaries take account of these increases in demand at higher frequencies of lift.
What do I do if I can't get hold of weight data for the items being handled?
In this situation, using the V-MAC won't help you with your risk assessment. You may need to ask your suppliers to tell you the weights or to mark them on each item.
What is the carry factor about?
Carrying involves effort by the worker and takes time. There are studies that have compared the effect on heart rate of lifting and of carrying. The carry factor uses this information to convert the total carry distance into an equivalent number of lifts.
What if carry distances are short?
Like the MAC tool, the V-MAC ignores carry distance if the average distance is less than 2 m – it treats it as a lift.
Do I need to enter carry distance?
No, the V-MAC will help you assess just the lifting part of the job. But if your workers are under time pressure then taking account of the carrying can tell you more about the demands on them.
Can I use the V-MAC to look at production jobs, not just order picking or warehousing jobs?
Yes. You will probably need to spend more time collecting the weight data than for jobs where a Warehouse Management System can tell you exactly what each person lifted.
Can I use the V-MAC to look at variability in other factors as well as weight and frequency? I'm thinking of the position of the item in particular.
No. Factors such as where the load is in relation to the worker can be assessed with the MAC. What you should do is follow the advice for the MAC and assess the 'worst case scenario' for each factor. In your case this would be for the 'Hand distance from the lower back', the 'Vertical lift region' and 'Torso twisting and sideways bending'.
The MAC website gives an example of assessing an worker lifting from a pallet placed on the ground. At the time you do the assessment the pallet may be half full and the worker may be lifting from waist height. Remember, at some point the worker will be lifting items from the bottom level of the pallet and therefore will be at greater risk.
The load weight/frequency factor is different to the other risk factors because there are complex relationships between the weights that are safe to handle, the frequency of lift and the total number of lifts. The graphs in the MAC and V-MAC help you look at these. Frequent lifting can be as hazardous as infrequent lifting – it depends on the weights being handled and whether or not the worker can take breaks or pauses.
As the load position moves away from the ideal position in front of and close to the body at around knuckle height, the risk increases so for factors such as 'Hand distance from the lower back' you need to look at the worst individual lifts. If you want, you can look at how many lifts a worker does over a day in the 'Close', 'Moderate' and 'Far' categories. A worker who does 1000 lifts in the 'Close' zone, 100 in the 'Moderate' zone and 10 in the 'Far' zone will be at less risk than someone who does 10 in the 'Close' zone, 100 in the 'Moderate' zone and 1000 in the 'Far' zone.
What about workers in extreme thermal environments, such as chilled or frozen warehouses?
You can use the V-MAC for jobs in these environments. Bulky clothing may slow down how quickly they handle loads. Workers will probably need to spend more time in other areas to avoid heat stress or getting too cold, so will have less time available for handling loads. There is HSE guidance on thermal comfort in hot and cold environments and on handling food in chill units and freezers.
Can I use the V-MAC to assess the demands on all my employees?
Yes, but you will have to spend more time doing the assessments. If the demands on each person are about the same you should find that doing a small number will be enough.
Is it OK for people to handle several items at once?
Yes. Handling several light items at once is a good idea because it reduces the number of lifts, so is usually quicker. Of course, if lots of items are handled at once, then the risk of the worker losing control of them increases. Also, the worker should not handle too many items and overload him/herself.
How do I find out if people handle several light items at once?
- Talk to them about exactly how they do the job;
- Ask them directly if they do this;
- Watch/video them doing the job.
The summary bars – what are they?
The graph shows bars for the mean, median and mode of the distribution of weights. These are all different types of 'average' and say something about the middle of the distribution.
- The mean is what most people mean by the 'average'. All the individual weights are added up and the total is divided by the total number of lifts.
- The median, or 50th percentile weight, is the middle value when all the weights are put in order. It is smaller than half of the weights and larger than the other half.
- The mode is the most common single load weight.
When the frequency distribution graph is a smooth bell-shaped curve, the mean, median and mode are all in the same place in the middle of the curve. This won't be the case in many assessments, which is why they are all shown.
The graph also shows the 25th and 75th percentile weights. These show how spread out the distribution is. The middle 50% of the distribution is between these two weights. The difference between the 25th and 75th percentiles is called the 'inter-quartile range'.
The 75th percentile is the middle point of the heavy half of the graph.75% of the weights are lighter than the 75th percentile, and only 25% of weights are heavier. Similarly, 25% of the weights are lighter than the 25th percentile, and 75% are heavier.
To take account of carrying, an adjustment is added on top of the bar for the mean weight. This works by converting carrying distance into an equivalent number of lifts.
What do the heights of the summary bars mean?
The heights of the summary bars indicate the overall demands of the job on the worker over a shift.
The colour zones change as the total number of lifts increase because very frequent handling will result in fatigue.
It is unlikely that a single weight would be handled enough times to reach the higher limits but the effect of all the lifting in a shift can be fatiguing even if all the individual weights are low.
The bars for the mean and median are all the same height. This is the total number of lifts entered into the spreadsheet — the total number of lifts over the shift.
The heights of the bars for the 25th and 75th percentile weights are half of the total number of lifts. This is because they mark the middles of the two halves of the distribution.
Sometimes I can see more summary bars and sometimes fewer. Why?
Sometimes the summary bars overlap. The Summary table gives you actual values for all the summary bars.