Second video in the "Risk assessment for mechanical designers" series
I'll start with the last slide of the first part. The mechanical designer, the electrical designer, and the CE representative need to talk to each other about risk assessment. To do that, all three of them need to know how to determine the risk index and the performace level. You do that in the risk assessment, and we're going to look at the heart of the risk assessment, which is assessing the risk of each identified hazard.
A machine completely without risks is rarely possible, so you need to be able to measure the risk so that you can assess whether it is still acceptable or not. This is done by using the risk index.
The risk index is an essential number for the mechanical designer. And to the electrical designers - please stay tuned, the performance level is determined the same way.
So you need to determine a risk index for the risk assessment, but how exactly you should do that is not completely set in stone. That's why there are all kinds of risk graphs. E.g.
- the risk graph of Safexpert
- the risk graph from Docufy
- the risk graph from Weka
And if you have seen the previous video, you can already guess which risk graph I use. I prefer Docufy. But I will also show that the others are just as good and lead to similar results.
All of them have the advantage that you don't have to determine the risk index in the scheme by hand - as I will show now - this is instead done by the software.
However, I would like to show you how to do it by hand now, because this makes the correlations clearest.
All risk graphs agree on the variables used to determine risk. And the same parameters are later used for the performance level.
Of course, the risk and therefore the effort I have to put in to avoid the risk depends on how severe the injury is that could occur.
But it is of course much more important to take care of a risk where people are constantly in the area of danger than if you pass by it only once a week. It's called the Frequency and/or duration of exposure to hazard.
And when you start to think about hazards on the machine, of course you have to worry primarily about the hazards that are likely to really occur and not so much about the ones that you can just imagine but are really unlikely. This is the Probability of occurrence
And some dangers can be avoided at the last moment by flinching away or the like. This is called the Possibility of avoidance or reduction.
So let's start with the first influencing variable - the severity of the possible injury. It is on the far left because it is the main influencing variable, to which all other variables are subordinate.
I like this classification very much because there is a clear distinction between S2 and S3, namely whether the injury heals and the person is fully capable again afterwards or not. But even this clear question is not so easy to answer in practice.
Let us look at an example.
Here, a lid is to be placed and locked in place. The lid is placed by the machine. To simplify locking, pressure is applied to the lid by machine. The operator locks the lid laterally. There is a pinch or shear point between the lid and the crate.
So you have to decide between S2: severe reversible injury and S3: irreversible injury. More about this in the next video - here just as an example to show how to work with the graph. I assume here a severe reversible injury.
Duration of exposure to hazard
A3 is the normal case. With this parameter the question regularly arises, how large my danger zone is and how I detrmined the size - but I will also speak to this in the next video.
Probability of occurrence
I would go for "unlikely to maybe" here - and as I said, more on that in the next video as well.
Possibility of avoidance
Here I would assume that you can still twitch away and therefore choose M1.
So we come to R6 and thus to the question, what do the colors mean?
Green means low risk. This can remain. This often involves unavoidable clamping points on industrial machines, such as when closing a protective flap. If the flap is not too heavy, you can put a gas spring on it, but you don't have to.
Blue means a medium risk and if the effort is not extraordinary high, you have to take care to reduce it. If you can't think of anything or the effort is not justifiable, your considerations should at least be documented in detail in the risk assessment.
Yellow means high risk. It can't stay that way.
And red is a very high risk, you probably weren't paying attention during the construction - but this does happen sometimes and should come to light through the risk assessment and then of course be changed.
And of course, the transitions are not as clear as they are shown here. It makes a significant difference whether the risk assessment produces R5 or R8 in the blue area. And the difference between R4 and R5 is also not as clear as the graphic suggests.
In our example, R6 had arisen - that is, a medium risk.
I would write that in the following way in the risk assessment.
This would be the first step as a risk without protective device. Next, you have to think about the risk reduction.
Now I would like to show that the other risk graphs produce similar outcomes and therefore it does not matter which one you take. For consistency only one should be chosen in the company.
Now to the other risk graphs:
As you can see, all variants result in a medium risk.
And to make these considerations, you don't have to buy the software from Safexpert, weka or Docufy. You can also do the evaluation manually, as I have just shown. You just have to choose a risk graph and write down your results for it. This can be, for example, in an Exel spreadsheet in witch you write your risks and evaluate them.
I have now deliberately chosen an example that can and must be solved without the help of a protective device - because that would be really expensive and would not be accepted in this branch of industry. The problem must therefore be solved by the mechanical designer.
And when such considerations arise, the following question should also be discussed: "Is this even relevant?" "Do we really need to worry about this?" The risk assessment is helpful in this question. The risk of getting your hand caught between the lid and the crate cannot be disregarded as minor. It is a medium risk and special considerations must be made to reduce this risk.
And I'll stop there, because much more needs to be said about the influencing factors before we get to the reduction of the risks.
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