but the holes remain — about ISO 13857 and others

Blacksmith’s hand will, statistically speaking, be slightly thicker than one of a fashion model — but the standards do not address this. Instead, the biggest divergence in defining the dimensions of the human body occur between standards for different types of machinery. Are there any significant anthropometric differences between a welding machine operator and a milling machine operator, though? And what does this have to do with safety?

As it is known, „guards and protective devices shall (…) be located at an adequate distance from the danger zone (Regulation^[1]until 2027 Directive 2009/42/EC is still in force, but these provisions are identical (EU)2023/1230 Annex III para. 1.4.1:d). “Adequate”, i.e. large enough so that it is not possible to reach the source of the hazard through (under, over, around) the guard.

Let’s focus on reaching through openings in guards. What distance is “adequate” depending on the size of the opening, i.e. how far can one reach through an opening of a certain size? The matter seems simple — if a finger fits in a hole, you can reach a finger’s length. But all fingers are not equal, even when looking at your own ten, and when building a machine we would rather have a specific criterion: a hole of size e makes it possible to reach over distance s. You can then see that we need to consult standards.

The standards harmonised with the Machinery Directive (or soon, regulation) define all the technical details which the directive would not have room for. But there are approx. 787 standards^[2]among the 1,215 entries in the list published by EC (version January 2023), there are standards that have already expired, as well as previous editions of standards that are still in force some time … Continue reading and they sometimes contain contradictory information, even on issues as difficult to justify as size of the openings.

Type B (general) standards

The general standards are used where there are no specific ones. So we have ISO 13857,^[3]EN ISO 13857:2019 Safety of machinery. Safety distances to prevent hazard zones being reached by upper and lower limbs and in it a table in dream form, i.e. how far by how tight. In addition, the openings are differentiated by shape, although there is not much choice — square, circle or slot (rectangle). Other shapes have to be accommodated in the ones given, which sometimes gives irrational results,^[4]example in the article about holes in guards but better something than nothing.

When determining safety distances, the authors took some shortcuts. The standard is designed to establish safe values for 95% of the population, so the dimensions of openings were based on the fifth percentile (meaning 5% of the population has body parts that are thinner or equal to the values specified in the norm), while distances were based on the 95th percentile (5% of the population has longer body parts). However, how many people actually have both such thin and such long arms? Perhaps 5% × 5%, which is 0.25% of the population, or maybe even less? In practice, the sizes provided in the norm are somewhat surprising — supposedly, a 21 mm wide gap is said to allow an entire arm to pass through at a distance of 85 cm.

Below are several values of a safe distance depending on the shape and size of the opening (Table 4 of ISO 13857).

opening size	circle	square	slot
e ≤ 4 mm	s ≥ 2 mm	s ≥ 2 mm	s ≥ 2 mm
e ≤ 8 mm	s ≥ 8 mm	s ≥ 15 mm	s ≥ 20 mm
e ≤ 20 mm	s ≥ 12 cm	s ≥ 12 cm	s ≥ 12 cm
e ≤ 40 mm	s ≥ 12 cm	s ≥ 20 cm	s ≥ 85 cm
e ≤ 120 mm	s ≥ 85 cm	s ≥ 85 cm	s ≥ 85 cm

The above refers to reaching with arms. If reaching with legs is considered (Table 7 of ISO 13857), the values are different, but the most interesting is the comment under the table that slots of width e > 18 cm and other openings (circle or square) of size e > 24×24 cm allow the whole body to pass through the opening.

There is another type B standard that also mentions the size of openings. ISO 11161^[5]EN ISO 11161:2007 Safety of machinery. Integrated manufacturing systems. Basic requirements, in section 8.5.2, states that the gap under the fence must not exceed 20 cm. Both mentioned standards are type B, so neither is more important than the other. However, since both are harmonized with the Machinery Directive, it should be assumed that in case of conflict, compliance with either of them is sufficient. This means, in particular, that vertical gaps in the fence may have a maximum width of 18 cm (according to ISO 13857), but the gap under the fence may have a height of 20 cm (according to ISO 11161).

Note 1. ISO 11161 applies to ‘integrated manufacturing systems’, i.e. assemblies of at least two machines operating together. So, if a fence installed 20 cm above the floor surrounds a single machine, this is non-compliant with the standard (ISO 13857). If an additional machine (table fan?) is placed in the same fence, the fence will be correct (compliant with ISO 11161).

Note 2. There is ongoing work on a new edition of ISO 11161. Instead of the current clause 8.5.2, there is only a reference (in clause 7.7.2) to ISO 14120,^[6]EN ISO 14120:2015 Safety of machinery. Guards. General requirements for the design and construction of fixed and movable guards which, in terms of guard dimensions, refers to ISO 13857. Therefore, when the new version of ISO 11161 replaces the current one, the gap under the fence will need to shrink from 20 cm to 18 cm.

Type C standards (for specific types of machinery)

Specific standards have priority over general ones, but their scope is limited to a particular type of machinery. As an alternative, protective measures recommended in a standard intended for a different type of machinery can be applied if the hazards are similar, especially in cases where there is no specific Type C standard available for the given machinery. For instance, when building a can sealing machine, it is possible to refer to standards applicable to presses. However, the principle of presumption of conformity does not apply in this case, meaning that building machine X in accordance with a standard for machine Y does not automatically make machine X compliant with the directive.

EN 619 — conveyors

According to EN 619,^[7]EN 619:2002+A1:2010 Continuous handling equipment and systems. Safety and EMC requirements for equipment for mechanical handling of unit loads the size from which openings can be significant is 5 mm for conveyors, as opposed to 4 mm mentioned in ISO 13857.

Some more important provisions are those concerning openings in the guards through which conveyors pass, specifically referring to the opening located above the conveyor, not around it (not beside or below). If the conveyor has a height of 1 meter or more, it serves as a sufficient barrier, and no additional guard needs to be placed above it.^[8]This corresponds somehow to the provisions of ISO 13857, where below Table 2 (Reaching over protective structures), for protective structures with heights ranging from 100 to 140 cm, there is … Continue reading

If, however, the conveyor is lower (even at floor level), the opening above the conveyor should be limited to a height of e ≤ 50 cm. It goes without saying that an opening that is one metre (or more) wide and half a metre high can be easily passed through without much effort — but in the case of conveyors, this level of effort is considered sufficiently discouraging.

It should be added that the standard recommends various solutions to make walking on the conveyor more difficult, such as limiting the width of a roller conveyor frame or filling the space between chains with a flexible mesh. However, it is not possible to secure a belt conveyor in the same way — anyone can freely walk on it.

EN 415 — packaging machines

Machines used for packaging have a series of standards known as EN 415, including EN 415-10,^[9]EN 415-10:2014 Safety of packaging machines. Part 10: General Requirements which covers general requirements for packaging machines. This standard addresses common aspects shared by standards ranging from EN 415-2^[10]EN 415-2:1999 Packaging machines safety. Part 2: Pre-formed rigid container packaging machines to EN 415-8.^[11]EN 415-8:2008 Safety of packaging machines. Part 8: Strapping machines EN 415-10 is an example of a Type C standard that describes various common aspects across different types of machines. Unfortunately, as mentioned above, if an assessed machine does not fall within the scope of EN 415-10, it cannot be referenced in cases where it conflicts with other standards like ISO 13857, as it is not a Type B standard. Therefore, the specific opening sizes described below apply only to packaging machines.

At first, regarding the gaps under the fencing. If the gap is not higher than 2 cm, the distances should be determined according to ISO 13857. But what if it is?

slot height	safety distance
e ≤ 2 cm	according to ISO 13857
e ≤ 4 cm	s ≥ 55 cm; s ≥ 13 cm “where access is not foreseeable”
e ≤ 24 cm	s ≥ 85 cm

At second, the standard introduces a division of openings into small, medium, and large categories. Small openings (e ≤ 120 mm) are distanced according to ISO 13857. The “medium” openings are further divided into small-medium, medium-medium, and large-medium (Ma, Mb, Mc) categories. There is a whole table dedicated to them, which determines the distances based on the shape of the tunnel guard and the presence of a conveyor in the opening, as well as 9 pages of example solutions.

The large openings (with width > 23 cm and height > 50 cm, or width > 50 cm and height > 40 cm), such as apertures for pallet loads, are protected by shields, light barriers, their combinations with pressure-sensitive strips, etc. These protective measures are muted during the passage of the load. To prevent people from passing between the load and the fence during the load passage, the distance between them (load and the fence) should be limited to e ≤ 23 cm. Why not 24, like the gap under the fence in the same standard? Just because.

And one more thing. If a conveyor is a component of a packaging machine, EN 415-10 refers to EN 619, but it specifies that the openings should be limited to 4 mm, not 5. Therefore, it may happen that a conveyor compliant with EN 619 (bearing the CE mark and the Declaration of Conformity) when installed in a palletizer… will no longer be compliant with the standards. So, what to do then – weld additional 1 mm on the rollers’ guards?

EN 13128 — milling machines

As the icing on the cake, we have a standard regarding milling machines^[12]EN 13128+A2:2011 Safety of machine tools. Milling machines (including boring machines) . The enclosure around an automatic milling machine can have a gap at the bottom with a height of e ≤ 30 cm. It even provides a method for checking the correctness of the fencing — “measurements to determine compliance with EN 294” should be conducted. EN 294^[13]EN 294:1992 Safety of machinery. Safety distances to prevent danger zones being reached by the upper limbs is an EU edition of ISO 13857 from the time when CEN issued everything with its own numbering. And now the riddle: how to „determine compliance” with ISO 13857 for slots wider than 18 cm?

conclusions

Most machines can be assessed according to ISO 13857. I am not aware of any case where a type C standard has more strict requirements than the general standard regarding openings (although this is different in terms of guard height requirements). However, it is worth referring to specific standards, especially when evaluating existing machines, as there may be instances where costly modifications^[14]A certain auditor in a certain factory noticed that the gaps under the fence were 205 mm high — non-compliant with ISO 11161. Following the recommendation, reducing the height of the gap, an … Continue reading are unnecessary.

Translated with much help from DeepL and Aria. Image by Freepik. The original title is taken from a Polish children’s rhyme:

„Pray, let me hear from each of you, whence came the holes in the cheese so true?”
The turkey replied, in a puzzled way, „I’m truly amazed, I must say.”
The rooster crowed with gallantry, „Who takes cheese seriously?”
The sheep stood pensive, in a trance, „I’ll go ask the ram, perchance.”
The horse spoke plainly and clear, „For me, it’s holes in the bridge, I fear.”
The dog sniffed the cheese in its entirety, „I smell a cat, a thief in the vicinity!”
The cat, pretending not to hear, Mewed, „Mice make the holes, my dear.”
Finally, the crow arrived at the scene, „The matter shall be resolved, serene,
I will make hole attempts right away, for I have a keen sense, I must say.”
She examined the holes with great care, measuring each, aware and fair,
Probing and selecting with precision, but where is the cheese? No cheese provision!
The turkey turned red, the sheep turned pale, „Great Scott! The crow devoured our cheese, a terrible tale!”
To which the crow replied from above, „You were concerned about the holes, my loves.
True, I consumed the cheese, it’s plain to see, but the holes remain, as you can agree!
For when I investigate, I don’t chatter, and what needs to be eaten, I do devour, no matter.
Alas, no one appreciates, it seems, the true sacrifice behind my schemes!”
And with that, the crow, feeling slighted, went away, her feelings ignited.

The Crow and the Cheese, by John Brzechwa^[15]translated by Aria, as I don’t have a translation by Walter Whipple or so; do you?