first video of the series "Risk Assessment für Engineers"
Does your company have a CE representative or a machine safety expert (or whatever the person who writes the risk assessment calls himself)? Many medium-sized mechanical engineering companies have such a person, and the large ones anyway. So why should you, as a design engineer, know how to write risk assissments?
To put it right from the start. You are not supposed to write the risk assessment yourself in the future. But you should know what exactly your colleague is doing. Why is that important?
Because in many companies, things don't quite work out the way they're supposed to.
In most companies I know, it goes like this:
The mechanical design department designs the new machine based on one of the previous machines. More or less things are to be changed at the customer's request. Maybe even a new function has to be built in. The mechanical designer works at the CAD and takes care of the functionality of the machine. In doing so, he proceeds as is generally customary and thus usually complies with safety regulations. He adds a protective device to the machine where it seems necessary to him.
When he is finished, the electrical designer takes over and makes the machine electrically functional. He has to take care of the movable guards. More precisely, he thinks about the safety switches and the safety circuits. He does it his way, usually without talking to the mechanical engineer.
Finally the CE representative starts his work. He writes a risk assessment for the finished product. Since most machines have performance level d, he can manage that, even if he can't change the machine any more.
This is a gross exaggeration. But in the exaggeration you can see particularly well what is missing. Communication is missing. And only with a lot of luck the right thing does come out of this process. To enable this communication, you as a designer should know how to write a risk assessment. Therefore, it is not enough if only your CE representative knows this.
And according to the Machinery Directive - which is enforced by law - you actually have to know how to write a risk assessment. The Machinery Directive dictates the following 3 steps:
Above, I have emphasized "in the order given". Because it is the design engineer who has to take care of machine safety first. That is by integrating safety into the design and construction of the machine. And in this first step, protective devices (like guards) are not yet allowed.
The standard again brings the same thing a little more succinctly.
- First, I try to achieve an inherently safe design as hard as I can.
- Only if I can't get any further, I help myself with protective devices
- And for the small remaining hazards - but they have to be really small - I can use warning notices
And who does what of these steps in your company? The inherently safe design is mainly up to the engineer. The mechanical designer determines how sharp a blade is, how much clearance there is between components. The electrical designer determines how fast components move and with what force. And only in the next step the protective measures are designed. The often used sentence: "It doesn't matter, it will get a protective device later anyway!", is not allowed according to the Machinery Directive. And remember, the Machinery Directive is the law for us.
The risk assessment requires that the danger points on the machine are evaluated for the first time directly after the design, when there is still no protective device on the machine. This is because the designer determines with his design the basic danger that emanates from the danger point on the machine. The protective device can then protect, i.e. reduce the danger. But the foundation is laid in the design, so the design must know how the risk is determined. This goes so far that extremely large hazards cannot be adequately covered by protective devices. Therefore, the correct mind-set is: "We add protective devices if there is no reasonably feasible way to achieve this function only."
Imagine a machine that is not completely housed in by protective devices. Only the places where a safe construction is not possible are secured with protective devices. This has the advantage of being able to put packing material and articles on while the machine is running. It has the disadvantage that the construction must be safe enough to allow for this. This is where the responsibility of the design is very apparent. Especially if you have big problems with tampering with your machine, you have to consider whether don't have too many protective devices – probably you should put more considerations into inherently safe design.
According to the Machinery Directive, protective devices should be added only when inherently safe design is not possible - which is often enough the case.
If protective devices are present, fixed guards or movable guards can be used. On my website, you can find out when you have to use movable guards. And of course a safety switch must be attached to every movable safety guard. For this purpose, it must be determined what has to be shut down when the protective hood is opened. The first answer I hear to this is usually "everything", but upon further reflection, enough exceptions come to mind that need to be considered. In most companies, the electrical designers make these decisions alone. But actually, the mechanical designer knows much more accurately how dangerous certain locations are. That's why both should sit down together and fill out a safety matrix, which the electrical designer then uses to program the machine.
And it's best to get the CE representative involved, because he has a really difficult job. He has to write in the risk assessment what the designers have thought. Generally, he - and I often do this as well - writes down what he thinks the designers might have thought. Actually, the designers should write the risk assessment, but unfortunately they can't because it's too extensive and it takes too much time to fill it out. Hence this division of labour and all the problems it brings. That's why CE officers have to be very communicative people and are considered annoying by some employees. And by the way, the CE representative has to make sure that the problems that have become apparent with one machine are also taken into account with the next machine and are then solved there in the right way, namely already during the design phase. And when we talk about risk assessment later and you perhaps watch these videos together with colleagues, you will notice that there can be different opinions as far as the evaluation of the danger points is concerned. Here, the CE representative has to act as a balancer, so that the company gives one risk assessment for its machines to the outside world and not different ones depending on the designer. And of course, the CE representative is the one who reads up on the standards, because this work should also be taken off the designers' hands.
All in all, writing the risk assessment in a really meaningful way requires a lot of communication between the mechanical design, the electrical design, and the CE representative. This works best when everyone involved is speaking the "same language". That's why all mechanical designers should acquire a basic knowledge of risk assessment.
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