I hear the argument you are making, John, but with the benefit of about ten years of experience dealing with the Machinery Directive I'm rather more positive about its approach. Since I believe the approach which the new LVD will take (when it finally get enacted) will be modelled on the Machinery Directive, I think it's worth spending a little time looking at this in more detail.
What the LVD does at present is it says "Here's a set of VERY basic safety objectives and here's a list of standards. If you apply these standards, you will (probably) meet the very basic safety objectives, and at very least you will have some evidence that you tried to meet the safety objectives even if you are ultimately found to have failed. Either way, you will be able to CE mark your product and sell it anywhere in Europe without having to meet any additional rules". What the Machinery Directive says is "Here's a detailed list of basic safety objectives. You HAVE to meet these except where they patently do not apply to your machine. If you want a yard stick against which to measure whether or not you have meet the safety objectives which apply to your machine, here's a list of standards you can use. Some of these standards are general, some of them are specific, but they all support one or more of the basic safety objectives of the Directive. If you use them you will (probably) meet the basic safety objectives, and at very least you will have some evidence that you tried to meet the safety objectives even if you are ultimately found to have failed. Either way, you will be able to CE mark your product and sell it anywhere in Europe without having to meet any additional rules". Superficially the approaches look very similar, but they are subtly different and, so far as the standards are concerned, the differences are immense. LVD standards are essentially comprehensive. In general, you need only apply one standard and it covers all of the hazards associated with a piece of equipment (OK, so where a standard has a General and a Particular requirement, you need two documents, but in theory at least they come together to make a single standard). Machinery standards are very different. The most important ones are called 'type B' standards and usually cover only one aspect of a machine's design. For example, EN 418 deals with emergency stops, EN 1037 tells you how to ensure energy sources are isolated, EN 999 tells you how to use light guards, EN 982 gives rules for the use of hydraulics, etc etc. There are maybe 100 or 200 of these 'type B' standards. Some machines will have only a few which apply, others will have many, but they are all oriented around providing guidance on the design of a particular aspect of machinery in general, rather than dealing the the overall design of a specific type of machinery. There are also hundreds of standards (so called 'type C' standards) which deal with specific types of machinery. For example, EN 693 deals with hydraulic power presses, EN 1494 deals with vehicle jacks and EN 201 is the standard for injection moulding machines. These standards contain lots of specific requirements for the types of machinery which they cover, but they also contain a lot of references to the 'type B' standards, and they may say things like "clause 1.2.3.4 of EN 123 does not apply to horizontal light curtains used on power presses with closing speed of less than 30mm/second". There are no type C standards which are self contained - i.e. which can be used without any reference to the type B standards. So, whenever one applies standards in support of the Machinery Directive, one is always going to have to pick and choose which parts of which standard to apply. This might not suit those of a nervous disposition who want everything laid out in black and white, but for more adventurous souls, who are prepared to get a grip on the process and use it to their advantage, it provides immense flexibility in how the standards are applied. The reasons for this are obvious. The scope of the Machinery Directive is so broad that it would be quite simply impossible to create type C standards for every different type of machine. One might argue, with some merit, that the scope of the LVD is no less broad in its own way, but I think an analysis will show that the hazards which are contained in most electrical equipment are of a lesser range than those in machinery. I have to say that the Machinery Directive approach provides a lot more exposure to poor standards writing since particularly the type 'c' standards committees are often populated by people with a particular axe to grind, and with too few others to be able to balance their position. I've certainly concluded that one should not necessarily believe everything which one reads in a type C standard. However, the Directive is very clear that you do not necessarily need to comply with the requirements of a standard, but if you do not you will need to justify in your Technical File how it is that what you have done as an alternative is adequate. The same possibility exists within the LVD of course, but it seems to me that lot's a lot less well understood or used. Overall, you really can't escape from the need for experience and expertise if you are going to successfully comply with either directive, and I realise that's not much comfort to people who are at the bottom of the learning curve. It's true of any engineering problem though (and it keeps people like me in work!). I'd also observe that the Machinery approach to standards is already starting to creep into LVD compliance. EN 50366 is a case in point - it's a standard which is focused on a particular type of hazard rather than on a particular type of equipment. Likewise, for anything with a laser in it, the LVD standard will probably refer to EN 60825 rather than trying to give detailed requirements for laser safety. The new LVD looks a lot more like the Machinery Directive, in that it has a much expanded set of essential requirements. I doubt we will ever see a wholesale re-write of all the electrical equipment safety standards to create a three tier structure such as the type A, B and C machinery standards, but I think we will see more new standards which deal with particular hazards rather than standards which deal with particular groups of equipment. Sory if this is rather long winded and boring, but it seemed to me it was worth putting on the record for those who are not already familiar with the Machinery Directive. Regards Nick. At 6:21 pm +0100 19/4/06, John Woodgate wrote: >In message <p06230916c06c146a6ccd@[192.168.1.62]>, dated Wed, 19 Apr >2006, Nick Williams <[email protected]> writes >>I do not agree. This approach may work for the LVD but it will >>rapidly lead to a dead end when applied to equipment within the >>scope of the Machinery Directive. > >Well, I was surprised to read what you wrote, because it's regularly spot-on. <SNIP> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
