What distance from the ground is the protective fence allowed to be?

If you have erected a protective fence around a machine or plant, you naturally want to make sure that it really prevents people from entering. And actually, the matter is quite simple. The standard specifies that the floor gap must not be larger than 18 cm. If it is larger than 18 cm, it is considered a full-body access, i.e. the standard assumes with a larger floor gap that someone can crawl under the protective fence.

18 cm! In my experience, no detail of the standards provokes as much discussion as this number. Who can fit through a gap of 18 cm? Nobody. With extremely high certainty, no one.

The other day, a customer said to me that if the floor slot is 20 cm, no one will fit through it either. And I have to admit, that's very likely true. So can I make the floor slot wider? Yes, you could, but then you would have to prove that no one would fit through a 20 cm slot to the customer to whom you sell it, which would be extremely costly and difficult - because how would you prove that? So it's better to go by the standard.

And the good thing about the standard is that if you adhere to the 18 cm and someone should still - however - crawl under the fence, you are clearly not responsible. The application of the standard protects you.

And don't be too tight with the 18 cm, because the feet are generally height-adjustable. You must take into account that the customer can also use the highest possible adjustable height of the feet.

Good, the 18 cm are clarified. So you have a distance of 17 cm from the protective fence to the floor. The whole body certainly doesn't fit under the protective fence. Then I often hear that the distance to the danger zone must then be at least 85 cm. Caution: This is not true. This is the distance that must be kept when fishing with the arm in the direction of the danger spot. But when it comes to the ground gap, you also have to assume that someone is fishing for something with their leg. If something rolls under the fence, I would first try to fish for it with my foot before lying flat on the probably dirty ground and fishing for it with my arm.

Since the leg would fit through a 17 cm slot, you have to assume the distance to the danger zone that can be reached with the leg and that is a distance of at least 1.1m. This applies up to a floor gap of 8 cm.

I like to take a ruler with me and measure up to the danger zone. Of course I don't measure up to the middle of the danger zone, which sometimes happens by mistake when measuring on the CAD, but up to the beginning of the danger zone - and 1.1 m is quite a lot.

If the danger zone is less than 1.1 m away, you have to pull the protective fence and, of course, the door further down. Namely, so far that, according to the standard, only the arm and no longer the leg fits under the protective fence.

If the gap is less than 8 cm, it is assumed that you can reach the danger zone with your arm, and this is where the generally known and in many places correct 85 cm distance to the danger zone comes into play. If the distance of the protective fence from the ground is between 2 and 8 cm, the distance to the danger zone must be at least 85 cm.

If the distance to the ground is so clearly specified as 18 cm, why do protective fence manufacturers also offer fences with a greater distance to the ground?

Well, the whole thing wouldn't be any fun if there were no exceptions. If your C-standard allows a larger distance, you may of course use it.

There is a special statement for IMS (Integrated Manufacturing Systems), for example, where a distance of 20 cm between the protective fence and the floor is permitted.

The C standard for packaging machines is also very generous in this respect.

But I don't know of any C standard that requires less than 18 cm of floor gap to prevent full-body access or is stricter than the B standard in any other way. Therefore, I think you will always get it right with the B standard. If any of you have or know of a C standard that requires smaller gaps, please be sure to post in the comments so I can look it up, because of course I don't want to put anything wrong here.

Yes, and then you can also find on the Internet the indication of 34 cm or 66.5 cm to the danger zone at 20 cm ground clearance. Here on the website of böma. Also on the website of Brühl-safety. Where does this come from? The manufacturers didn't make it up.

In the standard, there are statements about what to do if a ground clearance of 18 cm or smaller is not possible, e.g. because a vehicle has to move over ground that is too uneven. The distances given in this context are "not safety distances", but minimum requirements that hinder access, but do not prevent it.

Let me read this from the standard

"In some cases (e.g. mobile agricultural machines designed to move over uneven ground), the safety distances given in this International Standard cannot be applied. In such cases, at least protective structures to restrict the free movement of the lower limbs should be used. For this method, the values given in this Annex can be used.

NOTE These distances are not safety distances and additional precautions could be required to restrict access."

In the associated table, one then finds the 34 cm and the 66.5 cm.

These values cannot be claimed by any machine builder who builds machines for a machine hall.

So the dimensions we have talked about remains accurate.

If you would like to purchase a standards search, you can find it at

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