OT: Safety Catagories

Hello all. I was wondering if anybody knew where i could find information on Safety Catagories.

Catagory 1
Catagory 2
Catagory 3
Catagory 4

I was wondering if anybody knew the difference and when each one should be used.

EX: What catagory should be used if there is a chance of bodily harm to the operator??

Thanks in advance for all your help.

These are control categories as set out in the european standard EN954-1. the Pilz web site has good information, if you download the Pilz Safety book it will tell you everything you need to know.
http://pilz.com

The cut-off point for the hazard to a person is effectively at category 2.
Category 2 is OK if any hazard would not cause a permanent injury and Category 3 and 4 for a hazard that would cause irreversable injury or death. The other factor covering which category to use is the frequency of exposure to the hazard. The more frequent then use a higher category. For instance the difference between using a category 3 or 4 would be to use category 4 if there was frequent exposure to a possible fatal hazard and category 3 if exposure was infrequent to the same fatal hazard.

I was wondering if they would have the american standard. I suppose both standards are pretty much the same. Thanks so much for your reply.

Keldog said:

I was wondering if they would have the american standard. I suppose both standards are pretty much the same. Thanks so much for your reply.

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you might try the STI website.

Thanks again JohnW. There is lots of information in this website that will be valuable to me. I was wondering if you had experience in installation of safety systems such as light curtains.

I have to put light curtains on a machine in a plant and that's why i'm wondering what category of protection i need.

Well any who, you help is greatly appricatied.

I have some experience with light curtains on compression moulding machines and power presses to category 4.

We used the same cats. There was a dollar value attached to machine dammage as well. I don't remember the ammounts.


That was in a large wood products company, based in Washington State. I'm not sure if it is an American Standard or not. We only used it for internal incident reporting.

Keldog said:

I have to put light curtains on a machine in a plant and that's why i'm wondering what category of protection i need.

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Before fitting a light curtain to an existing machine it is best to determine if it is practical, you need to do a stop time test and calculate the distance between the hazard and the light curtain. Some machines take too long to stop for a light curtain to be practical or cost effective, I had one series of machines that the light curtains had to be moved 300mm further away because a stop time test showed that the original fit was too close. So its better to get this right first. Your prospective light curtain supplier might come in and do one for free, as it needs a special bit of test kit. The stop time is the time between breaking the light beam to the cessation of movement of the dangerous part of the machine.

Having determined that the stop time makes a light curtain practical then carry out a risk assessment to determine the control category that you need. Most light curtains come as cat 3 or cat 4 any way but you have to ensure that the rest of the machine control circuit meets the required category as well. There is no point in having a cat 4 light curtain if your control circuit is only cat 2 and you need a cat 3 or 4 system.

Thanks a bunch. All this information is extremly helpful. I will take this advice and apply it to my project.

Thanks again